Radio Boulevard
Western Historic Radio Museum
 

Shipboard Radio Receiving Equipment
1918 up to 1925

(formerly "The Classic Shipboard Wireless Receivers - SE-1420, IP-501 & IP-501-A")
 

1. Navy Department - Bureau of Steam Engineering - SE-143 - National Electrical Supply Co.
2. Navy Department - Bureau of Engineering - SE-1387 - National Electrical Supply Co. (NESCO)
3. Navy Department - Bureau of Engineering - SE-1834 - National Electrical Supply Co. (NESCO)
4. Navy Department - Bureau of Engineering - SE-1420 - Wireless Specialty Apparatus Co. (WSA)
5. Matson Line S.S. Mariposa - IP-501-A (Commercial) - Wireless Specialty Apparatus Co. (WSA)
 

Histories, Circuit Designs, Operation and Performance Testing

Restorations of SE-143, SE-1387, SE-1834, SE-1420 and IP-501-A

Operating 100 year old LF-MW Radio Equipment in
Today's Polluted Electro-Magnetic Environment

by: Henry Rogers - Radio Boulevard-WHRM

Navy Shipboard Radio Room  ca. 1925

According to RCA, the 1918 SE-143 was the first radio receiver available that performed adequately and was able to receive all types of signals whether they were from Spark Transmitters, Arc Transmitter, Alexanderson Alternators or from Vacuum Tube CW Oscillators. Surprisingly, RCA supplied manuals for the SE-143 as late as 1936. But, how could a WWI RF Tuner be in use onboard ships years after it should have been obsolete? UPGRADES! The SE-1387 and the impressive SE-1834 were especially designed, in 1922, to be used with the SE-143 (and similar receivers) to upgrade this WWI RF Tuner into a seven-tube TRF receiver with three RF amplifiers, a detector, a tunable heterodyne oscillator for CW and two stages of audio amplification. All accomplished externally with no modifications necessary other than wire-connecting these two devices to the already existing SE-143 terminals. After WWI ended, the radio receiver designs only got better with the SE-1420 Receiver that was introduced in 1919 and continued to be built as late as 1927. The SE-1420 paved the way for the incredible IP-501-A receiver that was used onboard ships and at coastal stations into the late-thirties with manuals available from RCA as late as 1938. The following examples of WWI and 1920s electro-technology illustrate how incredibly fast radio circuit designs and vacuum tube evolution were improving the communications equipment being built for commercial and military use.

Navy S.E.143 - U.S. Navy - Bureau of Steam Engineering
National Electrical Supply Company (NESCO)
SN:848N  Date on ID Plate - 1918

U.S. Navy - Bureau of Steam Engineering

S.E.143 - Short Wave Receiver - SN:848N - NESCO - 1918 Contract

The S.E.143 was a WWI Receiver that was essentially an RF Tuner (hereafter referred to as SE-143) It was used extensively by the Navy in the post-WWI era from 1918 up into the late-1920s (manuals for the SE-143 were available from RCA as late as 1936.) Other versions, like the IP-500 (usually built by Wireless Specialty Apparatus Co.,) were used on commercially-owned ships. The SE-143 was a sophisticated RF Tuner that provided a series LC Primary tuner and a parallel LC Secondary tuner. The Coupling coil between the Primary LC and the Secondary LC could be varied 90º and actually moved the coil from the control using bell-crank levers. An adjustable position Tickler coil (for VT detectors) was located inside the secondary coil form directly under a series-connected Secondary Coil extension to promote better feedback. The front panel TICKLER COUPLER control used a bell-crank lever control to rotate the Tickler coil 90º for regenerative feedback. There is also a large untuned additional Secondary coil mounted next to the main Secondary coil. The untuned secondary coil was to provide a broad response for tuning with external Crystal detectors or for finding stations transmitting on an unknown wavelength when using a VT detector. When searching for unknown stations, the Coupling was set to MAX for the strongest signal albeit not a very selective response. Once the station was found, then the SE-143 could be switched back to "TUNED" allowing the receiver to be further adjusted for the maximum signal level and best selectivity. Additionally, as the wavelength is decreased (higher frequencies,) the unneeded secondary coil sections are switched out (indicated on the schematic at 48-49 and 41-42.) The Primary Inductance also has switches to disconnect unneeded sections as the wavelength is changed (indicated on the schematic at 26-27 and 17-18.) The tuning range is 250M to 6400M or 1200kc down to 47.0kc. To allow the SE-143 to tune to VLF a Secondary Loading Coil, a Primary Loading Coil and a Tickler Loading Coil could be connected using the front panel terminals so marked. 

What the Specific Controls Do - The Primary Condenser dial has a 180º scale for half of the dial and linear scales for notations on the other half. The Secondary Condenser is calibrated in wavelength and also has the "letter designations" that were used during WWI and somewhat after as specifying important wavelengths (or frequencies.) Wavelength scaling is the figure shown times 100. A logging scale is also included in the other half of the dial. The inductance switches have letter designations on the Primary LC and numbers on the Secondary LC. The scales for the TICKLER COUPLER and the INDUCTIVE COUPLER are 0 to 180 with a MIN and MAX indication at each end. The scales imply the degrees of rotation for the specific coil. The BUZZER was used as a "potent" signal generator to be used when trying to find a sensitive spot on a crystal detector. The typical battery voltage for the BUZZER is no more than 2vdc if the buzzer is in good condition and adjusted correctly. There's spark gap between the ANT and GND terminals to provide a method to dissipate static charges on the antenna (common problem at sea or in windy areas.) Two sets of terminals are for LW loading coils that, when connected, allow the SE-143 to tune lower than it's 6400 meters (47kc) lower tuning limit. Various types of loading coils could be used (see vintage shipboard photo further down showing a DeForest Duo-lateral LW coil apparatus being used for VLF frequencies.) The DETECTOR terminals are provided for connecting the Crystal Detector. The eight vertically aligned terminals allow mating the SE-143 to the SE-1071 Audion Control Box. However, it's not specifically necessary to use the SE-1071. The terminals provide connections to the TICKLER COIL, AUD TEL, TELEPHONES (for Crystal Detector) and the receiver secondary LC outputs RA (grid-amplifier) and RE (ground-earth.) The SECONDARY SWITCH allows selecting TUNED or UNTUNED with the latter routing the SECONDARY  LC to an untuned coil that's closely coupled to the secondary inductance for a broad frequency response for easier tuning when using a Crystal Detector (it can also be used with an Audion detector when searching for unknown stations.) The DETECTOR SWITCH routes the secondary LC as necessary for either Crystal Detector or for an Audion detector.

from George Sterling's "The Radio Manual" 1st Edition - 1928

SE-143 Inside - RF Tuner only. Signal detection and amplification was an external function.

Cabinet Work - The SE-143 cabinet is made out of mahogany stained a dark reddish-brown color. The interior has no metal shielding installed. The right side front of the cabinet has two broken pieces of wood that are the full length of the height of the side piece. I had to remove the two latch-bails to be able to glue these pieces back correctly. The bottom front section is split and broken requiring gluing and clamping. I use Franklin's Genuine Hide Glue for this type of repair. This Hide Glue is not the old type (rendered from horse hoofs and hides) that needed to be a smelly, hot liquid that was quickly painted on and set-up as soon as it cooled. Franklin's is synthetic hide glue with all of the good properties and minus the disadvantages. This glue is amber colored and transparent so it looks old if it happens to show in the joint. It does take a fairly long time to set-up but the glued joint has to be clamped and let set for about an hour. For full strength the glue joint must dry overnight. Unfortunately, with these types of breaks, I have to use a combination of hand clamps and pipe clamps because of the distance between the glue joint and the back of the cabinet and because of the angle of the breaks. The need for pipe clamps is common with most cabinet repairs involving glued joints. The complete gluing took about a day to accomplish and used three pipe clamps and about half a dozen hand clamps.

I do have the rare front cover for this SE-143. It has had some crude repairs done to it. The cover piece of wood was replaced with 1/2" plywood, apparently many years ago. It's stained to a color that's sort of close and has a vintage-look to it. Also, one of the side pieces was replaced and the dove-tail joints not reproduced. Instead, the "dove-tails" were cut off and the wood nailed in place. It's pretty crude. Overall, the condition is probably a little worse than average BUT, at least, I do have the top cover, which is rare to find with an SE-143 receiver. 

The back of the cabinet ended up missing sometime in the past. Someone cut some 1/4" birch plywood, glued two pieces in a sandwich to create a 1/2" thick, stepped-type of back that fits okay. It wasn't stained and finished however, just left bare wood. Luckily, it's mounted with only four screws, so it can be easily removed for rework and staining. I have lots of red mahogany stain but I think I'll have to mix some golden oak in to get the correct color. I'll also work on getting a better fit, touching up the edges so they don't look like plywood and then stain to match. For the time period and that fact that most of the SE-143 receivers were expected to be "at sea" I'd expect varnish was the original finish used. However, after 100 years, there's not too much original finish left now.  NOTE: Close examination of the SE-143 cabinet with this make-shift cover removed seems to indicate that perhaps there never was a rear cover. I can't find any residue of glue, there are no nail or screw holes. I can't imagine that there wasn't a back to the cabinet,...I just can't find any evidence that shows how one would have been installed. However, since this make-shift cover fits and after staining it matches fairly well, I'm going to install it. If I find out later that SE-143 cabinets didn't have back covers, it can easily be removed.

The Hook-up - To operate the SE-143 with a VT requires a vintage triode tube and tube socket, an adjustable filament voltage source and another adjustable voltage source to provide plate voltage. A couple of things to observe are RE is connected to F- and B- is connected to F+. The 'phones are connected to the AUD TEL terminals. The plate voltage B+ is also connected the lower AUD TEL terminals that has one lead of the 'phones. The top AUD TEL terminal has the other lead of the 'phones but also has a jumper to connect the upper AUD TEL terminal to the lower TICKLER terminal (the use of the AUD TEL terminals was later found to be unnecessary.) Then the upper TICKLER terminal is connected to the Plate terminal on the tube socket. The jumper has to be externally installed because this connection was actually made inside the SE-1071. Additionally, the connections to 'phones, Tickler Coil and VT plate were all internal to the SE-1071 and controlled by a switch that selected OSCILLATOR (Regen going through the Tickler coil) or DETECTOR (Tickler coil shorted for a non-regenerative detector.)

The Ship's Generator as a B+ Source - Interestingly, the SE-1071 could provide B+ plate voltage either from storage batteries or it could be provided by the ship's +125vdc generator. There was an adjustable potentiometer to adjust the plate voltage but the +125vdc ship's generator only has a couple of filter chokes inline inside the SE-1071, so one has to wonder exactly what the plate voltage was and what the value of the variable resistance was (neither are indicated anywhere on the SE-1071 schematic.) There's a switch and terminals provided for selecting either storage batteries or the ship's generator as a B+ voltage source.

Vacuum Tubes Available in 1918 - Another consideration is the actual type of vacuum tube used in the SE-1071. In 1918, a Moorhead Electron Relay tube might have been used or perhaps a Western Electric VT-1. The UV-200 and UV-201 weren't introduced until around mid-1921, along with most of the other consumer-broadcast radio vacuum tubes, so they wouldn't have been used until that time. The WE-215A tube might have been available in 1919, but the special socket required for that tube seems to eliminate it for use in the SE-1071. The most likely VT used in 1918 would have been the WE VT-1 or the Electron Relay (there were several manufacturers for the ER type of VT during WWI.) For initial testing of VT detector and regeneration, I'm going to use the UV-200 and see how that works even though it couldn't have been used in 1918.

What Does Work - Finally, I decided to follow the SE-1071 schematic and hook-up closely. I used very short wire connections. I connected the 'phones one lead of the phones to the lower TICKLER terminal and the other 'phone lead to +45vdc. The upper TICKLER terminal was connected to the detector tube plate. Connecting to AUD TEL isn't necessary. I had connected the RE terminal to F+/B- but the SE-1071 has RE going to F- so that connection was changed. I replaced the 250pf grid blocking cap with a 500pf. I changed the grid-leak resistor from 1.2meg ohm to 680K (600K on the SE-1071 schematic.) I connected the grid-leak to B- as indicated on the SE-1071 schematic rather than in parallel with the grid blocking cap. I installed a 0.004uf capacitor from the junction of the 'phones and the Tickler coil as indicated on the SE-1071 schematic (although the value isn't shown on the SE-1071 schematic.)

Following the SE-1071 schematic and the hook-up exactly as shown resulted in tremendous regeneration capabilities with being able to easily adjust the TICKLER COUPLER for detector oscillations.

In actually operating the SE-143 and testing various wavelengths of reception, I've discovered that the detector plate voltage must be adjustable, as the SE-1071 B+ voltage was. The B+ supply must be capable of adjustment from about +20vdc up to about +90vdc. I've found that when operating the receiver at the higher frequencies, e.g., 400kc up to 1000kc, about +25vdc to +45vdc provides enough detector plate voltage for good regeneration and oscillating capability. The lower in frequency the SE-143 is tuned, the higher the detector plate voltage has to be adjusted to in order to maintain the capability of using the "untuned" TICKLER coil to get the detector to oscillate. At 100kc, I had to increase the detector plate voltage to about +70vdc for oscillation to occur. But, with +70vdc on the detector plate, I couldn't induce oscillation at 60kc,...that's just 40kc lower in frequency. The conclusion is that the SE-1071 Plate Voltage adjustment potentiometer allowed the user to adjust the detector plate voltage based on how easy it was to induce oscillations using the TICKLER adjustment. At 1000kc, only about +20vdc detector plate voltage will allow easy regeneration and oscillation. However, one also has to consider that all of the vintage photographs show the SE-143 and SE-1071 being set-up with some type of low frequency loading coils. The additional inductance on the Primary LC, the Secondary LC and the Tickler L would certainly help with regeneration when tuning below 100kc.

Adding a Single Stage of Audio Amplification - I have a Pilot Radio Redi-Blox Single Stage Audio Amplifier from about 1930 that I use with the SE-1420 receiver to boost the output of the detector tube for that receiver. It provides enough audio level to actually hear very weak signals, like NDBs, using headphones. I've also used this audio amplifier with the Spherical Audion Receiver with good results.

To hook-up the single-stage AF amp, the primary winding of the input transformer is connected to the two points where the headphones were connected,...to the AUD TEL terminals directly and with the B+ connection to the lower AUD TEL terminal and the one end of the jumper to the TICKLER COIL on the upper AUD TEL terminal. I use a UX-201A tube as the amplifier so about +4.5vdc connects to the filaments and I usually use about +60vdc on the plate and that is routed through the 'phones before going directly to the plate terminal. The F+ and the B- are connected to the B- terminal of the A-B power supply (B- is connected to F+.) Audio Output can be controlled by the tube filament voltage but normally I use the SE-143 Inductive Coupler or the Tickler Coupler to control sensitivity. A 1920s Horn Speaker could be used on just about any of the AM-BC stations. Hearing NDBs (the few left, anyway) will require 'phones. The NDBs are MCW signals but having the detector oscillating will make finding the NDB's carrier easy. Just tune for zero-beat and the MCW tone will be easy to copy. 

Regenerative Detector Set-up with UX-201A Detector Tube. Wire leads are as short as possible and clip-leads kept to a minimum. The A-B-C Power Supply is homebrew solid-state that I built about 45 years ago,...still works.

NOTE 1: The U.S. Navy created the Bureau of Steam Engineering in the 1860s as a technical engineering department, initially to help with the transition from sailing ships to steam powered ships. Later, new technologies like electrical and wireless engineering were added. In 1920, the name was changed to Bureau of Engineering and, in 1940, it was renamed Bureau of Ships.

NOTE 2: Interestingly, the data plate on SE-143 SN:848N has the wavelength "punch-stamped" as 250M(1200kc) to 3000M(100kc) rather than the standard 250M(1200kc) to 6400M(47kc.) 6400M was the standard longest wavelength tuned on the SE-143 and 6400 meters is what is shown as the lowest wavelength on the Secondary Condenser dial. I've confirmed that SN:848N does tune down to 6400M, so, for some reason, the data plate was stamped erroneously at "3000M." See photograph above near the beginning of this SE-143 section.

NOTE 3: The "Short Wave" designation is relative to the time period and to the typical frequencies that the Navy used during WWI. A more modern designation would be that the SE-143 is an LF/MW RF Tuner-Receiver (Low Frequency or LF is from 30kc to 300kc and Medium Wave or MW is from 300kc to 3000kc.)

SE-1387 - R.F. Driver (Tuned Heterodyne Oscillator)
  SE-1834 - Amplifier, Radio-Audio 125-30,000 Meters, Audio Universal
(3-stage Broadband RF amplifier, Detector, 2-stage AF amplifier)

Navy Department - Bureau of Engineering - National Electrical Supply Company (NESCO) - 1922 Contract
 

Post-WWI Radio Improvements - As radio evolved post-WWI, the need for new radio equipment was offset by the reduced post-war Navy budget that limited extravagant purchases to a certain extent. This resulted in the newest and largest Navy ships being prioritized for the newest equipment while an older or smaller ship would have to utilize older, maybe even WWI-era, radio gear. Improvements were much easier to fit into the budget and, as radio evolved, these external circuit additions allowed older radio equipment to be updated to provide usable service. Most peripheral equipment came in the form of RF amplifiers to be used ahead of a regenerative detector provided stronger signals and antenna isolation. Audio amplifiers to provide stronger post-detection signals to drive multiple outputs. Devices for interfacing specialized antennas such as loop antennas for direction finding. By 1922, there were several types of "add-on" devices available to improve the performance and usability of older receivers. This SE-1387/SE-1834 combination (shown to the right) was specifically for the SE-143, IP-500, SE-1220 or other similar RF Tuners.

Although the SE-1387/SE-1834 combination appears to be a receiver, it's far from being a "complete" receiver. The SE-1387 is actually a "tuned" Heterodyne Oscillator and the SE-1834 is almost a complete receiver but it's minus any selective RF tuning capability. Both units have to be used with RF Tuner sets like the SE-143. Unlike the earlier shipboard radio equipment that were housed in wooden cases, perhaps lined with metal shielding, the SE-1387/SE-1834 combo was built with an aluminum front panels and housed in an aluminum case. Both units are installed into individually shielded compartments to prevent any stray coupling between the units. The size of the metal cabinet matches the height of the SE-1420 so it's somewhat smaller than the enormous cabinet of the SE-143. Most Navy installations would place the "add-on" units on top of the SE-143 and wires interconnecting the units were routed around the panels to access the needed terminals. Although this particular example has the SE-1387 and the SE-1834 housed into a single cabinet, most vintage photographs show individual "add-on" units were single-function devices that were housed in their own individual cabinets (see the vintage photos further below.)

SE-1387 & SE-1834
Combination RF Driver and RF-AF Amplifier & Detector

RF Driver SE-1387 - 215-A tube socket & fil control. The Oscillator tuning condenser is controlled with a two-speed tuning dial assembly.

The RECEIVER terminals route the SE-143 RF Tuner output (RA) directly to the GRID INPUT of the SE-1834's RF amplifiers. The SE-1387 (oscillator) output is from the variable coupling coil inside the unit that is connected in series between the SE-143's RE terminal and the lower AMPLIFIER terminal that connects through an adjustable wire-wound resistance to the B- connections within SE-1834 (the STABILIZER control.) The Coupling Coil adjustment should be placed so that the letters on the COUPLING control nomenclature matches the letter of the tuning range selected. From that setting of the COUPLING, the output can be adjusted by slightly varying the Coupling Coil position to provide sufficient heterodyning to the SE-1834 but to not overwhelm a weak CW signal. In simple terms, the tuned LC from the SE-143 is connected directly to the SE-1834's WE 215-A RF Amplifiers and the RF Driver provides a heterodyne at the received frequency for CW reception from VT, Arc or Alternator transmitters. For Spark or Radiophone reception the SE-1387 could be turned off (turn the INCREASE pot fully CCW - like turning off the BFO.)

RF Driver SE-1387 - better view of Oscillator coils and the moveable shielded Coupling coil.

Universal RF-AF Amplifier SE-1834 - The front three units are four-band RF amplifier coils. The rear two units are Audio interstage xmfrs. The front three tubes are RF amplifiers, then the detector and the rear two tubes are the Audio amplifiers. The RF range switch selects one of four different, broadly tuned RF inductances in each RF transformer (selecting both the primary grid winding and the secondary plate winding.)

SE-1834 - Note the RF range switch. The meter is 2vdc FS and optimized for the 1.0vdc filaments of the WE 215-A tubes.

The Interconnection and Operation - The SE-143 RF Tuner was directly connected to the SE-1834's three stage, RF transformer-coupled RF amplifier by connecting the SE-143 RA and RE terminals to the RECEIVER terminals on the SE-1387. It was mentioned in the SE-143 manual that since the RA wire is a "grid connection" it had to be isolated, as much as possible, from other wires ("not bunched with the other wires" was the terminology used.) However, note that the SE-1387 terminals does provide a grounded SHIELD terminal implying that the RA/RE SE-143 connection should use a shielded cable. Internally, the RECEIVER terminals connect directly to the AMPLIFIER-GRID terminals and are "strapped" to the GRID INPUT of the SE-1834. This allowed the SE-143 a direct connection via its RA terminal to the first RF amplifier grid. The SE-143 Secondary LC ground-return is routed through the pick-up coil in the SE-1387 to allow the heterodyne oscillator to modulate the incoming signal to the SE-1834 RF amplifier grid (if the SE-1387 is powered-up.) Since the heterodyne is modulating the ground-return, there is a wire-wound resistance that's adjustable to "stabilize" the actual heterodyne versus signal ratio.

The RF amplifiers were broadly tuned via three RF transformers that provided four broadly-tuned ranges. This is essentially also where the incoming tuned radio signal was heterodyned with the SE-1387's variable-coupled oscillator output to allow detecting CW signals from VT, Arc or Alternator transmitters. The output of the 3rd RF amplifier stage was then routed to the detector stage. The output of the detector was routed to a two-stage, transformer-coupled audio amplifier. The audio output was routed to the TEL. terminals. Total gain was controlled by the filament voltage control and by the STABILIZER control. The purpose of the switch RADIO-AUDIO/AUDIO is to allow all filaments to operate in the RADIO/AUDIO position and turns off the filaments to the Detector tube and the two AF amplifier tubes in the AUDIO position allowing just the three RF amplifier tubes to operate (although this seems opposite of the expected function, measuring the continuity confirmed that the detector and audio tube filaments are turned off in the RADIO/AUDIO position. However, the nomenclature might imply using only the SE-1837 RF amplifiers ahead of the receiver's regenerative detector and audio stages.) The STABILIZER control is a wire wound resistance of the SE-143 RE connection terminal (secondary tuned LC ground return) to the B- line. The FILAMEOSTAT adjusts the filament voltage on the WECO 215-A tubes (set to 1vdc fil voltage.) For use of the SE-1387/SE1834 combo, the TICKLER terminals have the strap installed and the AMPLIFIER-GRID INPUT straps are also installed. If just the SE-1834 was used with an SE-143 RF Tuner, it would be possible to remove the TICKLER strap and use the TICKLER connections on the receiver for a regenerative detector. The RA-RE connections on the SE-143 would then be connected to the SE-1834 GRID INPUT directly.

There was an SE-1834A version that eliminated the filament voltage meter (shown in two of the vintage B&W photos further below.)

Circuit Analysis, Testing, Restoration - SE-1387 - There are no schematics available for the SE-1387 or the SE-1834. In fact, there's no documentation available, at all. I've had to trace the wiring to see what the circuits were intended to do when interconnected to an RF tuner like the SE-143. The circuit is a grid-leak oscillator with tightly coupled grid and plate coils. The grid coils connect to the variable condenser to allow the LC to function as a frequency adjustment. The range switch is double-function and selects both the correct grid coils and the correct plate coils simultaneously for a specific tuning range. The oscillator output is coupled by an adjustable "pick-up" coil (COUPLING) that is shielded with non-ferrous metal to allow magnetic pick-up only. The "pick up" coil connects in series between the SE-143 secondary LC ground return (lower Receiver terminal) and the lower Amplifier terminal. My analysis that the tuned oscillator is to provide an on-frequency heterodyne for CW reception is based on the increasing use of CW in place of Spark transmissions at the time and how later "Tracking BFO" TRF receivers were designed. Vintage photos helped to actually see how these devices were connected to the SE-143 in particular. However, the final analysis will be to confirm the SE-1387 does function as I think it should. This will require a functional WE 215-A tube. That should provide functionality for the SE-1387 and, with an oscilloscope and a LF-MW receiver, I would be able to see and hear the oscillator output. I've tested all of the coils in the SE-1387 and they all show continuity, so the testing will begin as soon as a good WE215-A is purchased and delivered. I did find a broken solder joint that was on the B+ buss to the plate coils (standard soldering technique of the 1920s using buss wire and "tack soldering" is very prone to breakage,...especially after 100 years on the Planet.) Testing has shown that the implied Filament voltage at the supply was 2.5vdc however, 2vdc is shown on the front panel.  This level allows the INCREASE pot to provide +1.0vdc to a .25A load at the tube filaments with the adjustment at about mid-scale (although the 215-A tube has sufficient emission well-below the +1.0vdc specification.) Also, A+ is connected to B- and both terminals are connected to the shield-chassis front panel ground. For initial testing (before I actually had a 215-A tube,) I used an RCA 864 tube that I connected into the circuit with clip-test leads. Amazingly, this did function exactly as expected but the final testing will have to wait for the 215-A tube.

The test set-up showing SE-1387 producing a 500kc (600 meters) waveform

The Test Set Up - I used an adjustable Lambda power supply with a voltage range of 0 up to +30vdc at 2.5A. I set the output voltage to +2.5vdc with the wires connecting to - and + FIL BAT terminals. The B+ power supply is an RCA dual bench supply with a range of 0 to +20vdc from each supply. I connected the two supplies in series to have +40vdc B+ with the wires connected to PLATE BAT + and - terminals. The SE-1387 monitoring was provided by the FNIRSI DPOS350P. This is a small, tablet-size, modern piece of multi-function test equipment that runs on a rechargeable battery. I'm using the oscilloscope to monitor waveforms. Also provided by the DPOS350P is the waveform frequency and the P-P voltage and a lot of other parameters of the waveform. Accuracy of the SE-1387 dial is good with 500kc showing slightly off from 600M. The 2.008mHz waveform showed 150M on the SE-1387 dial,...not bad for an oscillator that's over 100 years old.

Looking over the top of the SE-1387 showing the WE215-A tube installed, the 150K grid resistor, the non-ferrous metal shielded pickup coil and the grid-plate coils

Waveform on Range A at 150 meters or 2.008mHz VP/P=230mv

215-A in SE-1387 - UPDATE: I've run into this problem many times, especially on 1920s tubes. When the 215-A tube arrived, it looked NOS in the original box, but testing the filament continuity showed it was open. Visual examination with magnification revealed that the filament was intact. I re-flowed the solder on the base pins and checked again. This time I had continuity. I did the same re-flowing technique on the grid and plate pins. When the 215-A was installed, at first it didn't oscillate. I increased the filament supply up to +2.5vdc with the INCREASE control about mid-point for about +1vdc on the filament. The 215-A started to oscillate. I checked ranges A and B with no problems in operation. Subsequent testing confirmed operation on all five ranges. The filament of the 215-A is oxide-coated so as the tube is used it should continue to improve emission. Attaining full emission usually takes about 30 minutes of operation if the oxide is thorium-based. From then on, the tube will function correctly at a somewhat lower filament voltage (unless it's left inoperative for another 100 years.)

Waveform on Range B at 600 meters or 500kc VP/P=149mv

The Western Electric Co. 215-A tube - WECO 215-A tubes, also known as VT-5 or D-80039, are very similar internally to the WD-11 tube. However it's quite probable that the internal design of the later WD-11 that was used in Westinghouse-RCA battery operated Broadcast consumer radios from 1922 up to 1925 was actually based on the 215-A since Westinghouse and AT&T (Western Electric) were cross-licensed in the GE-RCA "Radio Group." The 215-A tube envelope and base are significantly smaller than the WD-11. The tube socket is unique and only fits the 215-A. Filament specs are 1.0vdc at .25A (WD-11 is 1.1vdc at .25A.) If the filament structure is like the WD-11/WD-12, then the 215-A uses an iridium-platinum ribbon that's oxide-coated. The 215-A behaves like a WD-11 in that filament emission takes place at a very low temperature and low current level (much lower than the .25A spec.) Most of the time, the 215-A filament isn't really incandescent at all but the emission is at specifications. In a day when a typical UV-201 tube required 5vdc at 1amp and the pure tungsten filament incandesced like a 5 watt lamp, the 215-A and the WD-11 behaved quite differently with many users unnecessarily increasing the filament current up to the point of filament incandescent visibility with disastrous results. Plate voltage maximum is +100vdc though usually the tubes are operated at +40vdc to +60vdc. The amplification factor is typically about 5 but could go up to 7 or 8 at higher plate voltages and if the tube has good emission. The 215-A tube was only used for a short time and was commonly found in the Western Electric Broadcast Monitoring Superheterodyne Receivers, like the 3-series and 4-series, also other WE BC monitors and apparently in a hearing testing device. Its common use was in the period of 1921 up to about 1928 although there are some indications that the Signal Corps had some use for VT-5/215-A tubes as late as the early-1940s. Although the WD-11, WD-12, WE239A and, the more modern replacement, the RCA 864 all have almost identical specs as far as the tube elements and function, the physical structure of these electrically-similar tubes is completely different. For initial testing, since I sold my collector tubes years ago that had included five good 215-A tubes, I'm going to have to buy seven of them,...ouch! The WE215-A is relatively inexpensive but the WE239-A is astronomically priced (WE tube dealers,...and for an anemic triode with an amplification factor of 5???) WD-11/WD-12 tubes seem to be somewhat fragile because most of the ones I've found had open filaments. I'm going to use the 864 tube for initial testing. It's a little more stoutly built and seems to function okay as a substitute. It's a moderately priced tube but I have several of them that didn't get included in the collector tube sale. I only used the 864 until I actually had a WE 215-A tube to use.

Circuit Analysis, Testing, Restoration - SE-1834 - Testing the functionality of SE-1834 is much more involved in that six WE215-A tubes are required for full operation. Point-to-point DCR testing has shown that both audio interstage transformers have good primary and secondary windings which is very helpful (and, yes, I do use that Triplett VOM for continuity testing as shown in the background of "The Test Set-up" photo above.) The 3rd RF transformer tests good for all four grid windings and for all four plate windings (it appears to be a vintage replacement.) The 2nd RF transformer has all four grid windings showing continuity but two of the plate windings are open (Band 1 and 4.) The 1st RF transformer has all four grid winding showing continuity but two of the plate windings show open (naturally, Bands 2 and 4.) All grid windings in the three RF transformers are good (that's 12 grid windings total.) Of the twelve plate windings, four are open and will need to be repaired. Due to the apparent failures in the plate windings involving all four bands, a bypassing of RF1 and RF2 would only leave RF3 in operation,...maybe okay for testing but RF1 and RF2 will have to be repaired for full operation. Due to the "iron core" type of RF transformers and the method of construction, any repairs to the windings will be difficult (but not impossible.)

All other components of SE-1834 test okay as far as DCR continuity. One broken solder joint was found. It was a buss wire that connected F+ from the STABILIZER adjustable resistor to the 3rd RF transformer grid buss connections. There are four spring-clip type holders that seem to be for grid-leak glass type resistors. Two are for the Audio tubes and are from the grid to B- which would imply they are grid-biasing resistors. I would guess the value would be 100K to 500K,...but that's just a guess. One other spring-clip is connected from the detector plate to the 1st AF interstage transformer primary winding. This implies that this also would be a resistor to compensate for the single +40vdc B+ to lower the plate voltage on the detector tube. The value would probably be less than 25K. The last spring-clip should be for the detector grid and should be a capacitor of about 250pf. So far, I haven't confirmed the detector grid connection. I found two, loose in the cabinet, glass capacitors that looked similar to grid-leak resistors but were marked ".002uf" on the inside (2000pf seems too high of a value for the grid-leak function.) These weren't installed but were wrapped in plastic and had been placed inside the cabinet. I'm not sure that any of the four spring-clips would use capacitors (although the actual grid-leak on the detector grid has to use a capacitor.) The circuit implies that resistance would be used. Drawing a schematic of the circuit would probably make the analysis a bit easier and certainly more accurate. Functional restoration of SE-1834 is definitely going to require complete disassembly. It appears that dismounting the tube socket chassis allows access to most of the components. To ease the process of disassembly and reassembly, a wiring assembly drawing (not a schematic) will have to be made.

SE-143, SE-1071, SE-1000 station at USN Station NAA. Those are impressive VLF loading coils. The tapped switches in front of the coils likely tune these inductances. This is a "non-posed" photo since the radio op moved his head during the exposure. Also the lighting and focus are not very good, however this is an incredibly valuable historical document of how radio equipment was set-up post-WWI.

The photo to the right shows a much later Navy shipboard installation (note the open porthole to the upper left of the photo.) This installation is using the SE-143 and on top left of the receiver is the SE-1387 RF Driver (or a similar type like the SE-1372,) then a duo-lateral LF loading coil assembly (possibly a DeForest LC-100) and an SE-1834A (no filament meter so it's the "A" version) on the far right. Although this receiver-combo can function in all modes, the transmitter is a quenched-gap spark type (though it might not be the only transmitter onboard.) The full-size version of this photo is the "header photo" above and actually shows another USN Officer standing behind the radioman. On the wall behind that Officer is a calendar. This photo is exceptionally well-focused with an excellent camera lens and, although partially obscured by the Officer, the year on the calendar can be read and is "192-" with the last digit not visible. A believable date for this photo would be around 1925.

SE-143, SE-1387 (or SE-1372?) a set of Duo-Lateral VLF Loading Coils and, at the far right, the SE-1834A. The transmitter is a Quenched-Gap Spark Transmitter. Note that the SE-143 is set to "CRYSTAL" on the Detector Switch. This might have been for the SE-143 to interface with the SE-1834A in this particular set up. The tuned frequency is fairly high as indicated by the Inductance switches. It's likely this was a "posed" photograph but it's still extremely informative as to 1920s shipboard "hook-ups."

 From USN Station NAA: (R to L) SE-1420 Receiver, SE-1372 LF RF Driver (?), SE-1597 Loop Antenna Amplifier, SE-1834A RF amplifier, detector, AF amplifier and a Receiving Antenna Coupler (being held by RMC Gilmour)  ca. 1925

NOTE: As can seen in the photo, none of these devices are interconnected implying that the equipment was probably arranged for the photograph and not necessarily that all of the equipment was "used" together.

IF these accessory devices were to be used with the SE-1420 then some circuit changes would be necessary since the SE-1420 already has a detector. It would be possible to use the SE-1387 (or the SE-1372) by itself as a Heterodyne BFO ahead of the SE-1420 detector by connecting the SE-1387 output to the SE-1420 Antenna terminal (just wrapping the output wire from the SE-1387 around the Antenna lead wire should provide sufficient coupling.) Then the SE-1420's TICKLER/regeneration can be adjusted to the point just before the detector oscillates. The only thing accomplished would be to eliminate the oscillating detector and replace it with a heterodyne oscillator. Actually getting sufficient  regeneration for oscillation is highly dependent on the frequency tuned, the detector plate voltage and the antenna used. The lower frequencies are particularly difficult to actually get the detector tube to oscillate. It's impossible to get the detector tube to oscillate at VLF unless loading coils are installed and the SE-1420 doesn't provide terminals for installing LF Loading Coils. A Heterodyne Oscillator would tend to make CW reception easier for a wider frequency tuning range without the use of LF Loading Coils.

The left-most unit is an SE-1834A and it might be possible to switch the SE-1420 control to CRYSTAL-RF AMPL to access the SE-1420's RF tuner section only by using the SEC COND and XTAL terminals and run the SE-1387 (as described in the preceding paragraphs) with the SE-1834. No battery voltages would be required for the SE-1420 since only the Primary and Secondary LC tuners would be used. A lot of experimenting was certainly necessary with these various pieces of equipment to achieve an actual functioning "upgraded" receiver. Integrating the SE-1834A with the SE-1420 would provide a TRF receiver with 3 RF amplifiers, detector and 2 audio amplifier stages. Adding the SE-1372 or SE-1387 would provide a heterodyne oscillator for CW reception.

SE-1420, IP-501 and IP-501-A Receivers
History, Design and Construction, Performance Testing
 

Louis Alan Hazeltine

The SE-1420 was designed for the Navy at the close of WWI by Louis Alan Hazeltine, who was a Stevens Institute graduate and later taught there. Hazeltine, in addition to teaching at Stevens Institute, was also a consultant to the Washington Navy Shipyard. A former student of Hazeltine's, L.C.F. Horle, was the technical leader at the Washington Navy Shipyard and the laboratory there was responsible for radio receiver design. Horle engaged Hazeltine to design a new wireless receiver for military use. What the Navy wanted was a receiver that could operate in the presence of nearby spark transmitters without interference and would allow stable operation while the detector was oscillating for reception of arc transmitters. The Bureau of Steam Engineering (changed to Bureau of Engineering in 1920) was in charge of Navy radio equipment at the time and most receivers were designated with the prefix "SE." Hazeltine's new receiver was going to be designated SE-1420. It borrowed a lot from its predecessor, the SE-143, in general appearance but, unlike its predecessors, the new SE-1420 was going to be a vacuum tube receiver. This went against all Navy tradition since the early days of spark. The Navy manuals of the day condemned the vacuum tube as "unreliable" and "power consuming."

photo from:  "How to Make Commercial Type Radio Apparatus" by Milton B. Sleeper - 1922
This Booklet profiles several commercial receivers and transmitters including the SE-1420 shown

Wireless Specialty Apparatus version of the SE-1420, probably from a 1920 contract. Tunes from 300 meters to 7500 meters.  Serial Number: 270R

Hazeltine first utilized a three-circuit tuner, that is, adjustable tuning of the antenna circuit, variable coupling to the tuned detector grid circuit and the detector plate circuit, to provide excellent sensitivity. He then used a completely shielded cabinet and isolated the Antenna Tuner circuit from the Secondary Tuner circuit with another shielded panel. This complete shielding would eliminate any stray pick up, hand-capacity effects or any coupling between the two circuits. Using a sharply tuned Antenna Tuner helped to improve selectivity and reduce adjacent frequency interference. By using a small Coupling Coil mounted inside the Antenna Coil and only allowing the energy from the Coupling Coil into the Secondary Tuner, further reduction of unwanted signals was realized. The two main inductors used bank-wound Litzendraht wire coils to reduce capacitive losses. "Dead turns" on all switched inductances were grounded by the action of the switches to further reduce losses. All of these efforts increased the selective nature of the SE-1420's tuning ahead of the detector input.

The regeneration, called "TICKLER," was provided by a variometer that was built into the secondary inductor form. One stator coil of the variometer was connected to the secondary coil while the other stator coil was connected through the rotor to the plate circuit. The wiring connections provide for the proper phase reversal for coupling between the plate and grid circuits to occur. The adjustment of the rotor position within the variometer allowed resonating the L of the plate to the grid circuit for detector inter-electrode capacitance feedback and also simultaneously increasing the EM coupling by way of the EM field intensity of the variometer and its relationship to the grid tickler stator coil allowing positive detector feedback and oscillation at the proper physical adjustment of the variometer rotor.

The detailed design effort was necessary because all Navy (and most other maritime vessels) used either spark or arc transmitters which usually produced very broad spectrum signals. Early receivers were so insensitive and tuning so crude that the broad transmitted signal was usually an advantage at attracting attention. The inability to have simultaneous operation of nearby stations led to sharing "airtime" - a gentleman's agreement that allowed most wireless operators to co-exist. Wartime was a different situation however and better, more powerful transmitters required better, more selective receivers. As the spark gap transmitter was improved by employing an oscillation transformer that narrowed the bandwidth, the receivers became more sensitive but not necessarily more selective. They still responded to the fairly broad spectrum signals that prevailed. At the time the SE-1420 made its appearance, its ability to function in the presence of nearby spark and arc transmitters made it an instant necessity for all sea going vessels. The photo to the right is from Milton B. Sleeper's 1922 booklet.

The Westinghouse Type RB Medium Wave Receiver (this receiver was in Ralph Muchow's Radio Museum located in Elgin,IL)
 photo from Radio Age, Nov '82

The U.S. Army Signal Corps BC-131 version of the SE-1420C. This example has the olive-drab painted wooden case. This is an AMRAD contact receiver that was rebuilt as a BC-131. The modification tag is mounted below the AMRAD tag and identifies the set as the BC-131.  Photo from Antique Radio Classified, cover, Nov. 2006

Tube types used in the SE-1420 depended on the time period and the end user. In early receivers, generally, if the Navy used the SE-1420, a Moorhead Electron Relay (ER) was used as a detector, while the Signal Corps preferred the Western Electric VT-1. There were many variations of the Moorhead ER tubes with different manufacturers building them from 1919 up to the early twenties. Both the VT-1 and the ER tubes specify filament current rather than voltage (.5A@ ~3vdc for the VT-1 and .4A@~4vdc for the ER.) There were other tubes also available, like the military triodes that had the internal structure mounted so that when the tube was operated in the horizontal position (as in the SE-1420) the actual tube structure is in the vertical position. This prevented filament sagging that could happen with standard tubes operated in the horizontal position. Later SE-1420 receivers used the 201A and these tubes specify filament voltage (5vdc@.25A) The panel meters were changed from ammeters to dc volt meters as tube use evolved.

Apparently, many early SE-1420 receivers were rebuilt by the military as the receiver aged. This included upgrading the receiver to the SE-1420C or BC-131 configuration. This upgrading included adding a grid-leak resistor and capacitor assembly, usually mounted on the Secondary Inductor mount near the Tickler coil. Early versions of the SE-1420 relied on self-biasing of the detector tube and, although this does work, it requires fine adjustments of the filament and plate voltages for best results since there isn't a fixed negative bias source in the SE-1420. As vacuum tubes improved, the grid-leak arrangement worked better since it allowed for rectification (detection) and would "leak" off the excessive negative charges quickly though a high-value resistor.

New SE-1420 receivers were built through most of the 1920s by several different contractors over the years. Shown in the photos to the right is the CGR-5A, made for the Coast Guard on a contract from June 1927. This version doesn't have the buzzer or the circuit selector switch and is housed in a metal cabinet. Also, the dial is calibrated in frequency rather than meters. The contractor on this particular CGR-5A was NESCO. This version also references itself to the SE-1420C as indicated on the CGR-5A data plate, "similar to Navy Type S.E. 1420-C/Army Type BC-131." The receiver shown belongs to Chris Dockery, who has also provided the photos. 

1927 - CGR-5A built by National Electrical Supply Company for the U.S. Coast Guard

The ID tag on the CGR-5A showing the contact date of June 6, 1927. The receiver was built sometime after that date.

History - IP-501 & Wireless Specialty Apparatus Company - In 1907, Wireless Specialty Apparatus Company (WSA) was formed by Greenleaf Pickard (who had cataloged over 1500 minerals and combinations that worked as detectors in 1903 - Pickard didn't discover the crystal detector, Karl Ferdinand Braun of Germany had invented the point-contact diode in the 1890s.) Additional WSA associates were Col. John Firth and his patent attorney, P. Farnsworth. John Firth also worked with Reginald Fessenden's NESCO at the same time and, probably because of this association, all WSA model numbers have the "IP" prefix which meant "Interference Preventer" - a Fessenden term for "selective tuning." United Fruit Company was an early user of WSA gear on their ships and in their shore stations. United Fruit Company had been somewhat in the radio business since 1903 and, in 1911, they bought WSA. Later, in 1913, United Fruit formed another radio company, Tropical Radio Telegraph Company, mainly for setting up and operating communications around their extensive property holdings in Central and South America. United Fruit was aware that their purchase of WSA gave them all rights to all Crystal Detector patents that WSA had through Greenleaf Pickard's association. The crystal detector dominated wireless receiver operation, especially through WWI. Right after WWI, the crystal detector patents were still of major importance and because of this patent, United Fruit Company was invited into the new cross-licensing agreement that was headed by General Electric and included Radio Corporation of America (GE's creation in 1919) along with AT&T (vacuum tube patents) and Westinghouse (Regenerative Detector and Superheterodyne patents and International Radio Telegraph Co.) With the cross-licensing agreement, these companies shared patents and products toward their advantage and tried to exclude most other companies and their competition by threats of lawsuits. The cross-licensing also allowed UF/WSA to now produce the SE-1420 for commercial users and have them sold by RCA (RCA hadn't created a division specifically to handle all maritime equipment and operate coastal communications stations - yet.). For the new commercial market, the designation of the receiver was changed to IP-501. A matching two-stage audio amplifier was now available, the Triode Type-B Amplifier. A Long Wave Adaptor was also available for operation at VLF frequencies. Though early versions may have used ERs or VT-1s, after about 1923, the IP-501 receivers used UV or UX-201-A tubes.

The IP-501 with Triode Type B Amplifier and Long Wave Adaptor.
    From: George Sterling's "The Radio Manual" 1st Edition - 1928

RCA/WSA IP-501-A from about 1923 to 1925, early version with Telephone Condenser switch and nickel-plated binding posts
 

History - IP-501-A & Radiomarine Corporation of America

In 1922, the IP-501-A was introduced. It combined the IP-501 and the Triode Type-B Audio Amplifier into one long cabinet. The consolidation made the IP-501-A easier to build since everything necessary was in one cabinet rather than two separate units as in the IP-501 and Triode Type B amp. The later versions of the IP-501-A eliminated the Telephone Condenser switch circuit and replaced all of the nickel plated binding posts with bakelite capped binding posts. At the time the IP-501-A was introduced, the general public had become interested in the new Radio Broadcasting. The market for entertainment radios sky-rocketed and most manufacturing concentrated on radios for broadcast reception. The commercial users were certainly not as numerous as the general public market and because of this the IP-501 and IP-501-A production level was never really very high. Wireless Specialty Apparatus built some home radios for RCA to sell, the AR1375, for example.   >>>

 >>>  RCA handled the sales of IP-501 receivers and accessories from around 1921 until sometime in 1923. By 1924, Wireless Specialty Apparatus disappeared from the scene, apparently purchased or absorbed by RCA. It's likely that RCA also acquired the WSA manufacturing plant in the deal since all later IP-501s and IP-501-As were built still using WSA parts. From 1924 up to sometime in 1927, RCA apparently carried on building receiver using WSA components and selling those marine receivers. In 1927, RCA acquired Independent Wireless Company and it was combined with Wireless Specialty Apparatus to form Radiomarine Corporation of America. Independent Wireless' Chas. Pennill became Radiomarine's Vice-President and J.P. Duffy came from RCA to act as Superintendent of Production. With the formation of RMCA, all marine operations and sales were then transferred to Radiomarine Corporation of America as a division of RCA. RCA had been operating many of the coastal wireless stations and providing "Radiogram" communications and those responsibilities were passed on to Radiomarine.
  

By the late twenties, the IP-501 family of receivers were beginning to show their age. The later versions eliminated some of the unnecessary or expensive circuits and parts but the basic style was still easy to recognize. Many receivers were still in use well into the late thirties. Their operation was easy, they were reliable and their excellent performance in the hands of experienced radio ops had resulted in the receiver becoming the "standard" shipboard receiver for at least a decade and a half. Advertising for RMCA was still using photographs of shipboard installations showing the IP-501-A as late as the post-WWII time period. The selling price of the IP-501-A was $550 in 1922 (listed in "Radio Enters the Home," a catalog of products available through RCA though built by WSA at this time.)
 

By 1930, RCA had acquired most of the patents and power that had formerly been shared by the GE-Westinghouse-AT&T Group as part of a settlement of an Anti-trust suit brought by the government. That resulted in the consolidation of RCA into the omnipotent corporation that controlled everything in radio in the thirties and forties. By the thirties, RMCA was running many of the coastal marine stations that provided Radiogram service to ships at sea. RMCA built marine radio gear that was installed on commercial ships. During WWII, RMCA supplied the Liberty ships with radio gear. Around the mid-1960s, RMCA was eliminated as a division and RCA handled all of the maritime business directly - at least, what was left of it.
 

United Fruit Company went on to political involvement in some Central and South American countries in an effort to protect and/or enhance their extensive banana and pineapple properties. Eventually, United Fruit Company merged to become United Brands (in 1970) and then was reorganized in 1984 as Chiquita Brands International.

both of these great photos are from: Grant Kornberg - "TechnoGallerie"

The Secondary Tuner circuit is labeled "SECONDARY CONDENSER" and "SECONDARY INDUCTANCE" - this is the main station selector tuning. The Secondary Inductance control selects the tuning range via the tapped inductance, "dead turns" are shorted to ground and the Secondary Condenser tunes the receiver frequency within that range. An articulated pointer shows which tuning range has been selected. On the IP-501 and IP-501-A, the Secondary Condenser dial is scaled in both Degrees and Meters with the various bands covering 300 meters up to 7500 meters, or approximately 1000kc down to 40kc and the condenser is gear driven, (most receivers will tune 1200kc down to 37kc.)

In some photographs, it appears that the first SE-1420 receivers may not have had a calibrated "SECONDARY CONDENSER" scale other than the 0-180º scale. If this was the case, it wasn't long before a meters calibrated dial scale was incorporated. That was followed by a dial with a meter scale and with important wavelengths marked off with letters. This must have been in reference to military wavelength assignments designated with letters because the SE-1420 lettered scale runs from "F" = 300 Meters up to "W" = 7500 Meters. The lettered scale is red while the meter scale is black. Late SE-1420 receivers, e.g. CGR-5A 1927, had dial scales calibrated in frequency rather than meters. Secondary Condenser dial from an SE-1420B receiver showing lettered scale. Also note that the receiver serial number is on the dial, "270R."

The detector is a regenerative type using a variometer and tickler built onto the secondary coil form. Variometer controlled regeneration relies on detector tube inter-electrode capacitance and the EM field coupling of the variometer rotor position relationship to the tickler coil (which is one of the stator coils inside the variometer.) For reception of damped wave spark transmitters using rotary gaps the "TICKLER" is adjusted to a setting just before the oscillation point. If an arc transmitter was to be received then the "TICKLER" can be set into oscillation to allow a heterodyne action (autodyne detector) to hear the arc signal since it is continuous wave or CW. For the reception of a voice transmission via AM, the "TICKLER" would be set to just before oscillation occurs. The greatest sensitivity and selectivity occurs just at either side of the oscillation point in a regenerative detector and that is usually where the operator would adjust his "TICKLER." Since the load on the "TICKLER" (plate variometer) is fairly constant (because of the Antenna Tuning) there is very little change in where the "TICKLER" is set until the receiver is operated below 100kc. Since the regeneration is tuned, lower frequency reception requires a little more total variometer inductance so the "TICKLER" control will have to be increased (higher on the scale) as frequencies below 100kc are tuned. The "TICKLER" tunes total inductance in 90º of rotation (sign changes happen in quadrants) but, depending on the receiver, all "TICKLER" action is usually centered around 45º and increases to 90º as the lowest frequencies are tuned. The push button switch labeled "OSCL'N TEST" is for testing if the detector is actually oscillating or not. If the button is pushed and the detector is oscillating a "click" will be heard in the earphones. No click means the detector is not oscillating and the "TICKLER" control needs to be adjusted. Detector tube is normally a UV/UX-201-A.

The Antenna Tuner section of the IP-501-A. Note the gear drives on the Antenna tuning condenser. Also, the Buzzer coupling to the Antenna circuit can be seen (the wire coil wrapped on the antenna inductance wiring.) The fixed condenser connects B- to ground (shielding.) The fixed condenser is a .012uf Faradon - the WSA/RMCA brand name.

The "TELEPHONE CONDENSER" switch allows selecting various values of input capacitors to the RF pi-filter that is connected between the output of the TICKLER variometer and the audio output line. The RF pi-filter also uses a series iron core choke and a fixed output capacitor. The selectable input capacitors allow varying the audio response, specifically rolling off the high frequency audio. This is particularly effective for relief from static and other atmospheric noise. This function is only on the WSA versions of the SE-1420. It is also on the early versions of the IP-501 and IP501-A. The TC switch was never used in the AMRAD SE-1420 and was eliminated from the later versions of the WSA receivers. The TC switch was really not a necessity. It was probably installed on the WSA receivers for shipboard operation where static and antenna noise can hamper reception. RCA/RMCA eventually eliminated the TC switch, probably because of expense, potential problems and the fact that an optimum fixed-value capacitor resulted in effective static relief along with increased reliability by eliminating the switch.

The "BUZZER" provides a "signal generator" of sorts. When looking for a sensitive spot on the crystal detector, it would help if a really loud signal was present. Pressing the buzzer button will actuate a small mechanical buzzer that arcs and creates tremendous wideband RF. This is coupled into the antenna circuit with a brass sleeve capacitor on the wiring to the Antenna Inductance switch on SE-1420 sets and by a wire coil wrapped around the same wiring in the later receivers. The buzzer battery is usually a 1.5vdc dry  cell battery. It's not critical, but 2vdc was considered the maximum for the buzzer. DO NOT PRESS the buzzer button (with Buzzer battery connected) while in the vacuum tube mode of operation - if you do and you're using 'phones in the AF2 jack, the resulting "signal" will be so intense that you probably won't be able to hear anything for a few minutes afterward (yes, I did it.) The Buzzer circuit was only for finding a sensitive spot on a crystal detector. Additionally, a Long Wave Adaptor was sometimes used if operation below 40kc was needed. This unit sat on top of the receiver and its connections match the binding posts located at the top of the panel on the IP-501 and the IP-501-A (the Long Wave Adaptor units were not used with the SE-1420.) The Long Wave Adaptor had series inductors inside that when connected allowed the receiver to tune down into the VLF part of the spectrum.

The Secondary Inductor switch assembly. Tickler control  is on the right. Note the vertical gear-driven "lifter" for the dial pointer. The wooden shaft under the TICKLER control is the OSCL'N TEST button. This unit is from the SE-1420 receiver.

The copper shielding inside the IP-501-A cabinet is painted black. Note the divider shield and the small notched opening that allows the two wires from the Coupling Coil to pass through to the Secondary Tuner. Also note that the tapped screw mounts that allow the panel to be mounted are connected to the box shielding and these mounts also contact the back panel shield for a completely shielded enclosure.

The oak box that the receiver is mounted in is entirely lined with copper sheeting to act as the shielding. Complete contact is assured by way of the metal screw mounts that contact the receiver's panel shielding. Early receiver boxes sometimes had a front cover that was held on with bale clamps. The ID tag is located on the side of the box and these are almost always missing. This was probably due to the "military surplus" regulations of the time that required all mil-tags to be removed before sale. Something about if the tag wasn't there then the unit wasn't stolen. This regulation may have also applied to commercial surplus. Weight of the box with all of the copper inside is substantial and the entire receiver is quite heavy for a battery operated receiver - about 40lbs for an IP-501-A. The box for the SE-1420 is similar in construction but the shielding is not painted and is left bare copper. The finish on the SE-1420 box is somewhat dark, usually about the color of "iced tea." The later IP-501 and IP-501-A receiver boxes are finished in golden oak. Most BC-131 boxes are olive-drab paint. The front panels are .312" thick and is made of "Hard Rubber" sometimes called "Condensite" or "Bakelite-Delecto." This material is not brittle like bakelite or formica. The manuals say that the panel can be wiped with oil to protect it. Probably, with all of the salt-air present onboard a ship at sea, wiping oil on the entire panel, dials, knobs and cabinet would have gone a long way to protect the receiver's overall finish.

All screw and nut connections in the receiver are tightened and then soldered. This method is also used on the mechanical assembly. Soldering is easily accomplished since all of the hardware is nickel plated brass. This securing of all joints with solder was necessary because of the constant vibration of the ship while at sea in addition to adding protection from salt-air corrosion problems. The solder joint itself is not particularly strong and can easily be disassembled, however, much like modern "loc-tite," it was meant to keep the screws and nuts secure after tightening.

Restoration and Operating the SE-1420, IP-501 and IP-501-A Receivers

Most SE-1420, IP-501 and IP-501-A receivers that are found today are far from complete. It isn't unusual to find the receiver missing all of its buss wiring or missing major components and almost always some of the minor parts will be gone. I one time found the Antenna Tuning Condenser of an IP-501 that had been "sawn" out of the front panel - not dismounted from the panel - just sawn out, panel and all. Such destruction was common. Anything is possible to find since these receivers were considered surplus unusable junk in the forties and fifties. How likely your receiver is able to be completely restored depends on your interest, your abilities at replicating parts and how much of the receiver you have to start with.

SE-1420, IP-501 and IP-501-A  -  Schematics and Documentation

Documentation is very important when restoring the SE-1420, IP-501 and IP-501-A receivers. To say that they were poorly documented would be an understatement. None of the schematics available are complete. Most will provide a general idea of how things are connected but details are certainly lacking. The various schematics are shown in several books, e.g., Elmer Bucher's book on Wireless Equipment or early editions of George Sterling's Radio Manual or others, but all are incomplete schematics that are only provided as general information. The IP-501 schematic shown to the right is about as good as they get. Not a lot of details but it is basically complete and does show the connections to the complicated "Circuit Selector" switch. However, mistakes are common, e.g., the "Grounding Condenser" is not a variable, it is a fixed condenser. This schematic is good for the IP-501 produced around 1922. Earlier SE-1420 and the later IP-501-A are very different receivers. What one has to do is use good photos of the interior of original receivers combined with the information provided in the better schematics to ascertain what is correct for your particular receiver. This is assuming that your receiver needs to be restored and is missing some of the original buss wiring or original components. Be aware that the buss wiring techniques and routings changed over the production period, so early receivers look very different inside from the later versions of the same model. Interior photos are the most helpful to determine what is correct.

Operator's manuals are around. Some are available on the Internet and some basic operating instructions are included in various books. Sterling's "The Radio Manual" has instructions for both the SE-1420 and the IP-501, along with the Long Wave Adaptor. However, these instructions are brief, contain very few details and are not completely accurate anyway. No details are provided about typical antennas for the receivers. The RCA and RMCA manuals are by far the best and most accurate.

Helpful Hints in Restoring the SE-1420, IP-501 and IP-501-A Receivers

Synchronizing the Tickler Variometer - The variometer has to increase total inductance with the proper sign (+ or - are used to indicate the increase or decrease of total inductance as the rotor turns inside the stator coils) as the pointer is advanced up the TICKLER scale. This results in the receiver requiring higher TICKLER settings as the wavelength is increased (lower frequency.) The correct wiring is the detector plate is connected to one coil of the variometer stator as the input. The grid circuit is wired to the other stator coil to provide the feedback path. The variometer rotor output (rotor-front) goes to the Circuit Selector Switch, RF pi-filter and on to the audio output and detector B+. To check that the variometer is synchronized, place the TICKLER pointer straight up on the scale. Look at the variometer rotor just visible on the shortwave side of the Secondary Inductor and you should be able to see the wire splice joint that connects the two rotor inductors together. If you don't see the splice joint then the rotor is 180º out. Remove the TICKLER knob and pointer, then rotate the variometer rotor so that the splice joint side is visible, then re-install the knob and pointer with the pointer straight up on the scale (or nearly straight up.) Check the flexible connections on the variometer rotor to make sure they aren't coiled too tight at each extreme of TICKLER adjustment. NOTE 1: Although you do get a change of total inductance through each 90º of rotation with a variometer, the two 90º quadrants in 180º of rotation are of opposite sign + or - (there is a mutual inductance change also.) When the variometer is operated in the opposite two 90º quadrants, the receiver will not regenerate on lower frequencies or will oscillate uncontrollably due to improper phase relationships to the grid coils. With the proper variometer synchronizing the receiver's oscillation is controllable on all tuning ranges.
NOTE 2: Some receivers (early SE-1420s) will have the variometer rotor mounted slightly off so that the angle of rotor rotation is not 0-180º. This was probably to allow the TICKLER adjustment to be more "mid-scale." Later receivers have 0-180º rotation and most of the TICKLER action is located in the 0-90º portion of the scale (as would be expected.) This allowed plenty of regeneration at the lowest frequencies that the receiver would tune to since this was about mid-scale (90) on the TICKLER adjustment.

Dismounting the Primary and Secondary Condensers - The condensers are mounted using 10-32 screws and nuts with stand-offs between the condenser mounting plate and the back of the panel. The nuts are secured by soldering after assembly. To remove either condenser first remove the associated fine adjustment knob and the dial by removing the large knob and collar, then remove the dial. The dial is only held in place with two locating pins and should easily come off. You will now see that the flange that the dial mounted to will just barely fit though the hole in the panel shield. You have to be careful not to bend the shielding too much when removing the condenser otherwise you will end up shorting the condenser to the shield when reinstalling the unit. Unsolder the buss wire connections to the condenser. Then remove the screws and nuts. The soldered nuts will come off easily. Solder is not particularly strong and usually with a open-end wrench on the nut and a large screw driver on the screw head, the solder joint comes loose with minimum effort. You can also heat the joint up with a larger soldering gun or iron and then break the joint loose. Heated solder is even weaker and the screws will loosen with almost no effort. After the screws and nuts are off, carefully rotate the condenser assembly while lifting it off of the panel. You will find some interference between the panel shield and the dial flange but by rotating the assembly, the flange will clear the shield hole. Be sure to check the shield hole for bends - it should be straight and even with the back of the panel. Be sure to keep track of the four stand-offs. Remount in the reverse order.

Dial Pointers - These are rather complex assemblies for the simple job they do. The "lifter" mechanism is located on the associated inductance assembly. The lifter is gear driven by the inductance switch and the lifter itself is attached to a rack gear. Two guides keep the rack's alignment. The lifter has a "L" shaped bakelite piece that the pointer pin is inserted into. The pointer itself is mounted to the front panel by a two-piece cover-guide that is nickel-plated. The cover-guide is mounted to the front panel with four 2-56 round-head machine screws. To remove the pointer just take out the four guide screws, remove the cover-guide pieces and remove the pointer from the lifter by pulling it away from the panel. If you need to work on the lifter mechanism itself, you will have to remove the associated inductance assembly.

Automatic Filament Control Wiring for IP-501-A - I've not seen a schematic for an IP-501-A that shows the wiring of the Automatic Filament Control Jack system. However, the system was used in several other battery operated radio receivers/amplifiers and the wiring should be the same. The telephone jacks have to control both filament voltage and plate voltage based on into which jack the telephone plug is inserted. This requires special telephone jacks that have enough auxiliary contacts to accomplish the switching based on whether or not the plug is inserted. Federal Telephone & Telegraph Company was a major supplier of Automatic Filament Control Jacks. The following information is from the 1923 Federal Tele. & Teleg. Co. catalog and show the jacks required, their identification numbers and how to connect them for automatic operation of the filaments in a Det + 2 Stage AF Amp, like the IP-501-A uses. Click: Automatic Filament Control Jack & Circuits

Buss Wire Details - Buss wiring changed as production methods evolved. The early SE-1420 receivers use a reddish-brown varnished tubing (spaghetti) for insulation. The wiring style for these receivers is very square and the buss wires actually run much longer than necessary. This was for appearance and was typical of the style of wiring at the time. When the IP-501 and IP-501-A were being produced by RMCA, the varnished tubing was changed to black. The style of wiring also changed in that the runs are much shorter and though still somewhat square looking, there are some angles and bends that are for better durability or performance rather than appearance. The late IP-501-A receivers still use black varnished tubing but more and more the square-look is giving way to more direct connections. Finally, in the 1927 CGR-5A (SE-1420C) the spaghetti is entirely eliminated and enameled buss wire used. When replacing missing buss wire, try to find an interior photo of a comparable receiver for reference. Buss wire was usually 13 gauge tinned-copper, which is impossible to find. I have used 14 gauge and 12 gauge, both work fine, although the 12 gauge is more difficult to work. Before using either size, the wire should be "drawn" - that is stretched by anchoring one end and then pulling the other - hard. This straightens the wire and slightly reduces it's diameter. It will make the buss wiring look very straight and professional. 

1918 - Initial design of the SE-1420 by Louis Hazeltine
1919 - First contracts for the SE-1420 - AMRAD, WSA and Sperry Gyroscope
1919 - RCA is formed from GE assets and purchase of American Marconi Co. (Nov-1919)
1920 - SE-1420 contracts are extended
1920 - Cross-licensing with GE-RCA group allows WSA to offer SE-1420 as commercial IP-501
1921 - Design of the IP-501-A
1922 - IP-501 and IP-501-A available from RCA acting as sales agent
1923 - Likely purchase of WSA assets by RCA.
1923 - SE-1420 contracts continue, National Electrical Supply Co. added to list of builders
1925 - Production continued on IP-501-A using Faradon and WSA parts by RCA
1927 - Official formation of Radiomarine Corporation of America
1927 - IP-501-A updated - eliminated Telephone Condenser switch, bakelite capped binding posts
1927 - CGR-5A (SE-1420C) contract, National Electrical Supply Co., June, 1927
1928? - Production continues through 1928? 1929? 1930?...
1930s - Manuals date-stamped as late as Dec.1938 were provided by RMCA
1940s - IP-501A receivers used up to 1940, removed prior to and during WWII

Restoration of the IP-501-A

Back in 1979, I bought this IP-501-A from a ham friend who had traded a telephone pole for it. The price of $75 took into consideration the substantial amount of work that was going to be required to restore the set. Back then, with no Internet, all parts had to be advertised for in Radio Age magazine with the hope that one of the many collector-readers might have what you needed and would be willing to sell the part. It wasn't unusual for part locating to take a year or more. The IP-501-A was missing almost all of the buss wiring, it had the incorrect AF transformers, the Telephone Switch was gone along with the correct tube socket assembly. Additionally, the set's front panel was in pretty rough condition as were all of the nickel-plated hardware parts. The cabinet was actually in pretty good condition and the parts that remained were also in good condition. My first restoration just got everything cleaned up and looking good but I didn't want the IP-501-A to be just a "shelf queen" so I began to advertise for specific parts I needed to get it operational. That resulted in the second, functional restoration. I used black plastic tubing for the "spaghetti" on the new buss wiring and the interstage transformers were two old Jefferson units. I had to make several parts. I made the tube socket assembly from .25" thick original vintage bakelite. The nickel-plated tube socket shells came from an old TRF battery set. One small knob had to be cast in epoxy resin with black filler so it would come out looking like hard rubber. The metal parts that had to be made were two binding posts and one knob pointer. I got the IP-501-A running and eventually wrote an article on it for Radio Age (April 1984 issue.) Don Patterson (editor for Radio Age) sent me some material on the IP-501-A that included an article written on the IP-501-A receiver back in the 1960s for Popular Electronics. The article had a good photograph of the inside of an original IP-501-A, something I had never seen before.

The IP-501-A as I received it before any work was performed - April 12, 1979. This photo shows the deplorable condition that the front panel was in. Since the front panel is hard rubber, it is easy to aggressively clean it with soapy water and 0000 steel wool. It sounds harsh but the panel can take it and this cleaning method removes all of the staining that is usually found on these receivers.

As received April 12, 1979. This photo shows how much was missing inside. Note that most of the buss wire is gone, the non-original tube socket assembly is made out of masonite, the AF transformers are Ferranti units. Luckily, the meter, the filament pot, the phone jacks and the tube socket frame were original parts. See photos in the above sections for what the restored interior looks like.

My second restoration had been incorrect in several places and needed to be redone to be an accurate representative of the IP-501-A, both physically and operationally. I started to search for more parts for the new restoration. The easiest to find were the two RCA audio interstage transformers. The new buss wire used was now 12 gauge (I had used 14ga. before) which also was easy to find. The lacquered tubing or "spaghetti" was a reproduction product supplied by one of the few dealers then around and doing business. It looked very close to original.  The Condenser Switch and assembly was rebuilt from correct vintage parts and then installed in a painted black, brass metal box I made. All of the hardware on the front panel was removed and then cleaned and re-nickel plated. The tuning dials were listed originally as "German Silver" but that is really just a fancy name for heavy nickel plating that has a small amount of copper in the plating anode. In order to have all of the hardware parts match, since some were new repros, I had to re-nickel plate all of the hardware. That way it all matches and looks the same vintage. Disassembly is difficult because all screw and nut assemblies are soldered. The technique for removal is to use the soldering iron to heat the solder and nut, then while the joint is still hot use a nut driver to remove the nut.  While hot, the solder isn't very strong and the nut will back off with very little effort. Clean the screws and nuts before reassembly for better solder flow. This last restoration was done in 1984 and resulted in the IP-501-A looking original and functioning as it should. Or did it? I found that I could not get the receiver to oscillate below about 250kc no matter where the TICKLER was set. Reversing the variometer leads got the receiver to oscillate but the wiring layout didn't match photos of original IP-501-A receivers. I finally revised the way I had done the buss wiring which then allowed the variometer stator input to connect to the plate and the front of the variometer rotor to be the output. This got the IP-501-A looking correct inside and working the way it should - able to regenerate down as low as the receiver would tune.

Restoration of the SE-1420

I bought this SE-1420 from a fellow in Louisiana who had advertised it in Antique Radio Classified magazine in 1990. He had listed the radio as a "Radiomarine Corp Receiver." I was curious as to what it was so I called and asked him to describe the receiver to me. When I heard "...,two large metal dials, lots of metal binding posts and an oak cabinet...," I was sure it was an IP-501 receiver. The price of $150 plus shipping took into consideration that the receiver was nowhere near complete and had been extensively modified by someone, circa 1940s. The seller described all of the modifications and indicated that no major holes were drilled and the coils and condensers were present. When the SE-1420 arrived I found he had described it very accurately. The most important parts to have present on these types of receivers are all of the coils, condensers, bandswitches, dials and cabinet. Most of the other parts can be found or replicated. It seems to be common to find these types of receivers with most or all of the buss wiring missing. Also, many times they are found with conversions to later vintage tubes. Most of the time this is the work of "hamsters" (radio amateurs who are all too eager to modify vintage equipment into something it was never intended to be.) The SE-1420 family was available surplus in the late thirties and most of the modifications seem to date from that time period.

 This SE-1420 had all of the essential parts so now I just had to find all of the missing parts. First on the list was a buzzer which was easily found, though it's a Federal T&T type SC BZ-1 (Signal Corps) which is not the original make. I made a replica buzzer switch. Next, I needed a suitable meter. Although a CAY-260 ammeter meter is correct for this vintage SE-1420, I was only able to find a similar vintage Weston DC Voltmeter with 5vdc high-lighted in red. It is not technically correct but probably imparts better information when actually operating the receiver (besides, later SE-1420s had filament voltmeters and probably those receivers updated by the military also had DC voltmeters installed.) Two metal pointers had to be made and two replica knobs cast. The tube access door was missing its knob but a very similar brass type was found at the hardware store, although I had to nickel plate it. A Federal T&T low-capacitance lever switch was found on the Internet (probably after I had owned this receiver for at least 12 years.) 

Replicating the SE-1420 Tube Socket
The early versions of the SE1420 have a complex, spring suspension tube socket mounted on long standoffs. Later versions eliminated this over-designed, expensive-to-build socket with a simple bakelite platform and standard bayonet-twist type socket. The elaborate suspension socket has an incredible 77 total parts to the assembly, including 12 conical springs and dozens of nuts, washers and screws, not to mention the three mounting rings that hold everything together. There are 21 parts just in the three standoffs that mount the socket to the panel. I delayed restoring the SE-1420 beyond "shelf queen"  for almost twenty years - mainly because of the difficulty in replicating this socket due to a lack of detailed information. Over the past several years, I collected various vintage photos that showed the spring socket from various angles. Finally, in 2009, I had enough information (and interest) to go ahead with building a replica spring socket (and hopefully completing the SE-1420 restoration.) Building any multi-part assembly is certainly made more difficult when a physical example is not available to examine and measure, or a detailed mechanical drawing doesn't exist. Using five vintage photos I was able to use proportional measuring to determine the size of the various parts that comprised the tube socket. This method involves measuring existing parts from my SE-1420 and then measuring the same parts in the photos to determine scale and then extrapolating what the measurements of the socket parts should be. I created several scale and non-scale drawings to "figure out" how this over-designed mechanism was going to work.

77 parts are required for the Tube Socket

I had a local machinist make the standoffs, the shouldered screws and the metal base plate based upon my drawings. I made all of the bakelite pieces and the tube contact pieces. The socket shell and tube pin contacts were from a 1920s battery radio and found in the junk box. Assembly was fitted together to check everything and then, when I was sure of proper fit, the brass screws and nuts were soldered. This duplicated what was normally found in shipboard receivers and was done to prevent assemblies from shaking loose during the constant vibration encountered while at sea. I had to fit brass spacers (like thick washers) inside the springs to keep them centered. From the vintage photos, it appeared that the main support springs had extension spacers. I soldered brass extension spacers to the springs where necessary. The bakelite wire carrier ring has rubber insulated wire connections coming from the tube pin contact strips. These were routed as seen in the vintage photographs. UPDATE 2026: With SE-1420 receivers showing up on eBay once in a while, I've seen some very good photographs of original spring-suspension tube sockets. My replica is pretty close in appearance and functionality. Of course, nickel plating the springs and other brass parts should have been done. I should have used non-threaded rods for the spring-suspension assemblies. Original examples have cotton wadding pushed into the springs, probably to reduce microphonics. But, other than those minor points, the 77 piece replica socket looks pretty much like an original.

The inside of the Telephone Condenser Switch showing the contacts, capacitors and choke.

A close up from a different angle showing the buss wiring, the TC condenser switch and the tube socket after installation. The original tube sockets had cotton wadding pushed into the springs to dampen movement and reduce microphonics.

"Patina" is a very important part of replicating old parts. I deliberately left the washing residue on the tube socket and also judiciously added scratches and marring to the TC switch box paint. I used a chemical "patina" to darken solder joints and to darken the brass parts of the tube socket. This imparts the impression that one is looking at original parts, original soldering - a true vintage replication.

I did install one upgrade to the SE-1420 which was a grid-leak RC to improve performance with 201A tubes. This was a common upgrade done by the military in the early-twenties as vacuum tube performance evolved and improved.

Cabinet Restoration
The top of the SE-1420 cabinet was severely water damaged. The oak wood was almost rotten and all of the original finish was gone long ago. Fortunately the bottom still had some original finish left for matching the color. The early SE-1420 cabinets are darker than the later IP-501 receivers. The good finish on the bottom was about the color of "iced tea." I had to remove a lot of damaged wood from the top by heavy sanding. This damaged wood was soft and came off like coarse wood fibers until I finally got down to undamaged wood. There were many, many holes drilled in the case over the years. I filled these with wood filler. The rest of the case was in good shape and only needed minor touch-up. After one coat of finish, I touched up all of the "filled holes" with artist's acrylic mixed to match the finished color. This way grain can be painted in on the filled holes and they will blend in with the rest of the wood. I finished the case in amber shellac and boiled linseed oil. This probably wasn't original but it can easily be removed if I ever do find out what was used as the original finish. The finish is deliberately left "flat" - no gloss - to give the impression of originality.

Performance Testing 100 year old Radio Receivers

Operating the SE-1420
 

The SE-1420 during testing. The receiver is on (note filament meter) also filaments of the 201A tubes can be seen. The Pilot Radio Redi-Blox single stage AF amplifier is on the right. The 'phones are Baldwin Type E "Super Sensitive." The receiver is tuned to PBT 338kc (as seen on the frequency counter.) PBT 338kc (called Proberta) was located in Red Bluff, California. Details on using a digital frequency counter for an accurate frequency readout are included in the section below "Operating the IP-501-A."

The initial test was on the AM BC band since signals there are very strong. As soon as the voltage was applied the SE-1420 started to "squeal" through the earphones - a really good sign for regenerative receivers. Backing the TICKLER down brought in the local (Reno) AM BC station on 920kc. A slight tuning of the Antenna Condenser had that station coming in strong in the "Baldie" earphones. I tuned in a few more AM BC stations with very good results, so now it was time to try "NO", the non-directional beacon (on 351kc) at Reno-Tahoe International Airport. Switching to tuning range to "2" and Antenna Tuning to "3", "NO" was found quickly. Since NDBs send MCW signals, the signals are easier to find if the detector is oscillating. In this mode, the Coupling is more critical and most controls interact significantly. Stability is also very difficult to achieve but the SE-1420 seemed to be fairly stable with a UX-201A tube. This isn't the tube type that was normally used with these receivers but this was just a test of operation.

The next step was to try the Western Electric VT-1 and then the Moorhead ER, both typical tubes used with the SE-1420 back in 1920 or so. The WE VT-1 works very similar to the 201A tube except the filament voltage is 3.0vdc. The TICKLER settings and the condenser settings are very close to that of the 201A. This indicates that the WE VT-1 has similar inter-electrode capacitance to the 201A tube. Not so for the Moorhead ER. This tube runs about 4.0vdc on it's pure tungsten filament. TICKLER has to be advanced significantly and even though it is sensitive enough, it is difficult to tell when the tube is oscillating. Again, this is an indication of the different inter-electrode capacitance specifications for the Moorhead ER when compared to the 201A.

Using a UV-201A tube, I was able to "tune in" 28 NDBs in a 30 minute period that evening. Greatest DX was YZH 343kc, Slave Lake, Alberta, Canada. Pretty good results for a single tube receiver. I next added a Pilot Radio Redi-Blox AF amplifier (ca. 1928) to boost the signal levels a bit. This is a transformer coupled, single stage audio amplifier using a UX-201A tube. With more audio, DDP 391kc in Puerto Rico was received (~3500 miles from here,) also YMW 366kc in Maniwaki, Quebec. Low power 25W marker beacons like SYF 386kc in St. Francis, KS and SBX 347kc in Shelby, Montana were also copied. In all, in two listening sessions, 50 NDBs were received including one newly heard 25W NDB, PA 396kc in Snohomish, Washington.

 Incredible performance from a 1920 regenerative receiver. NOTE: I performed this SE-1420 testing while in Virginia City, Nevada in late-February 2009.

Operating the IP-501-A


The RMCA IP-501-A during testing. The receiver is on (note the filament meter) and is receiving local NDB, "NO" Reno-Tahoe Int'l AP on 351kc (as seen on the frequency counter.)  photo date: Feb 2009

"NDBing" with the IP-501-A
Since the IP-501-A was a shipboard receiver designed just after WWI, its primary intended use would have been in the 600 to 3000 meter wavelengths that most maritime radio operators used. The fact the receiver happens to cover about half of the modern AM Broadcast band is handy for checking receiver operation but most of the AM BC signals are so powerful they could be picked up with a good quality crystal set. The real intended use of the receiver would have been tuning from 100kc up to 500kc. Nowadays, there are perfect signals in that part of the spectrum to really test the capabilities of the IP-501-A. Those signal are NDBs,  Non-directional Beacons. These are relatively low powered beacon transmitters located at many airports around the world. The NDB's only transmission is to send their station ID in Modulated CW (MCW) every few seconds. USA NDBs generally run 25 watts to various kinds of antennas, from high quality verticals to crude end-fed wires. Some coastal and regional beacons run from 400W up to 2KW. Canadian NDBs are very numerous and usually run at higher power levels than those in the USA making their NDBs relatively easy to receive. NDBs would be a great test for the IP-501-A since they are MCW, low power and numerous - pretty much like the old time maritime signals (only not as broad.)
Power Requirements
To power up the IP-501-A requires 6vdc at about .75A "at the front panel terminals" for the A+ tube filaments (so the voltage can be adjusted for ~5vdc required for 201-A tubes,) 45vdc B+ for the detector plate and 90vdc B+ for the amplifier plates. A -4.5vdc C bias is also required. I generally use a Lambda 6vdc 4A power supply for the filaments but I have also used rechargeable batteries (however the power supply is more convenient to use.) For the B+ requirements I use a mid-twenties RCA Duo-Rectron B Eliminator which uses an 874 cold cathode regulator tube and a UX-213 full-wave MV rectifier tube. With the Duo-Rectron, regardless of the load, the B+ voltages remain constant. The -C bias can be supplied by a small battery since the load is negligible. I made my C battery out of three AA batteries for -4.5vdc.
Antenna, Ground and Audio Requirements
The antenna should be at least 75 feet long and worked with a good ground system. I have used a 75' sloper antenna that did a pretty good job. My best results came from my ham station antenna which is a 135' center fed tuned dipole with open feedline but with the feedline shorted and then connected to the ANT input. This, theoretically, results in a vertical antenna with a large capacity hat similar to the large "T" antennas of the twenties. It seems to work very well for MW and LF reception. I also use the ham station ground system. For the audio output, I used a set of Western Electric 516-W earphones. These are typical ferrous diaphragm type 'phones with a DC R of 2200 ohms. I tried to use a set of Baldies (Baldwin Type-E) but due to their design with direct driven diaphragms, they were "too loud" and seemed to respond to various types of noise better than the signals.
General Operating Set-up 
When operating the IP-501-A as a non-oscillating regenerative detector, the COUPLING can be preset to the desired selectivity. Higher settings (tighter coupling) provide stronger signals but less selectivity. Lower settings (looser coupling) will increase the selectivity and can reduce signal strength. Generally, anywhere around mid-point will provide strong signals and fairly good selectivity. When the receiver is operated as an Autodyne (oscillating regenerative) detector, setting the COUPLING becomes more involved since many of the controls interact in this method of operation. You can set the COUPLING precisely by using the "Critical Coupling" method (described in the next section on Tuning in NDBs.)TICKLER is the regeneration control and this setting adjusts the sensitivity of the receiver. Usually the TICKLER is set to just before oscillation (regenerative) or just after oscillation (autodyne) for best sensitivity. 

IP-501-A Testing Results
During my set-up for test-listening, I pre-set the receiver to around 770M. When power was applied, to my surprise, there was SX 376kc, a Canadian NDB up in Cranbrook, BC (it was only about 4:45PM local time.) That night, during a 30 minute period, I tuned in 25 NDB beacons from 326kc up to about 414kc. Best DX was DDP 391kc in San Juan, Puerto Rico. This is a 2KW transatlantic beacon but it is about 3500 miles from Virginia City, Nevada. Most difficult was probably ULS 395kc, a 25W marker beacon in Ulysses, Kansas. Subsequent sessions have tuned in YMW 366kc in Maniwaki, Quebec, also YY 340kc in Mont Joli, Quebec, both at about 2500 miles and IY 417kc in Charles City, Iowa, a 25W marker beacon. Additionally, Radio Rossii, the LW BC station on 279kc, located on Sakhalin Island was received, along with PN, the NDB at Port Menier, Anticosti Island, Quebec. In the three week period of 1/21 to 2/11, I tuned in over 100 NDBs with the IP-501-A - seven were never-before-heard NDBs. Impressive performance from an 87 year old (then, in 2009) three-tube regenerative receiver.  

IMPORTANT NOTE for 2026: Nowadays this type of NDB reception is impossible with any type of MW receiver, even modern MW receivers. The sheer number of NDBs that have been decommissioned since 2009 is staggering. None of the USA pilots use NDBs for navigation anymore and that's resulted in most airports having decommissioned their NDBs. The few NDBs still in operation are not used for navigation in the USA. The airport is using the NDB as a radio "airport identification" signal and the transmissions are kept running as an "airport navigation tradition." In addition to NDBs, many of the other traditional navigation signals are being removed from the LF and MW spectrum in the name of "modernization." Airport economics is certainly another factor in the removal of most NDBs, so don't expect these few remaining NDBs to be in operation too much longer,...at least in the USA. Canada is also decommissioning their NDBs at an alarming rate.

IP-501-A NDB Log - Jan 21 to Feb 11, 2009
The following is the log of the NDBs copied using just the IP-501-A receiver and the 135' tuned dipole antenna with the feedline shorted. NDB location, frequency and power (if know) are listed. This reception test was performed in Virginia City, Nevada, my QTH at the time.

Total as of  Feb. 11, '09 is 103.

Kilocycle to Wavelength in Meters Conversion Chart

* = Newly NDB heard

1. Turn off everything you can in your house and see if the noise goes away. It's amazing, but LED lamps that don't cause any interference above the AM-BC band sometimes cause intense switching noise below 500kc. Light dimmers are also notorious noise-creators. Wall-wart power supplies, various types of computer accessories, modern modulated furnace blowers, neon pilot lamps,...and just about anything "SMART." If just switching off everything in the house doesn't find the culprit then maybe the noise is external to your house.

2. External noise can be from any of the devices mentioned above but located in your neighbor's house. Modern real estate trends have houses built with virtually no space between houses making the proximity of RFI-creating devices much closer than they were (are) in older neighborhoods. Solar panel "levelers" and "inverters" can be very potent RFI sources. Reports are that the more modern versions of these devices have eliminated the noise,...maybe. Older street lamps using Hg-vapor or Na-vapor lamps can be very intense RFI polluters if the lamp is failing and switching on and off. Most new street light installations are using LED type lamps and they don't seem to create RFI. Some external sources can be "fixed" but most can't.

3. If the RFI isn't from your own house then, usually, the listener has to come up with their own solutions to eliminate or, at least, reduce the RFI noise pollution. The most efficient device to use is the shielded-magnetic loop antenna. This type of antenna is very effective at reducing RFI noise. These loops work great on receivers that were built after WWII. The Pixel Loop performs quite well below 500kc and can be used (without too much loss) down to 150kc. Depending on the receiver's front-end design, sometimes S-M Loops won't work very well,...especially with early, 1920s receivers. This mainly due to the Primary LC Tuner's fairly high impedance that was designed for an end-fed wire antenna. The S-M Loop's 75Z input impedance is far too low to work well with early-twenties receivers. It's possible to use an "un-un" balun designed for high-Z end-fed wires and hook-up it up backwards so the loop antenna is fed to the Lo-Z side and the Hi-Z side goes to the receiver. I've successfully used this method with a Rycom LF Receiver that had a 3500 ohm antenna input impedance. Unfortunately, the large wire array antennas that can perform quite well in rural areas can't be used in metro-urban areas.

In urban areas, with major industry running 24-7 and millions of potential RFI creators, listening on MW and LW is going to be impossible. Going mobile to a rural area, operating on batteries and using some sort of "strung-up" antenna is the usual method for LF and MW listening for urban dwellers. Suburban areas might have individual RFI noise polluters that can destroy any MW or LF listening with their EM RFI noise, but usually these sources can be dealt with by using a shielded-magnetic loop operated with an impedance matching "un-un" or other such Lo-Z to Hi-Z matching device. Generally, large wire antennas can't be used because of space limitations and there still is quite a bit of RFI noise in suburban areas. Unfortunately, most manufacturers don't care whether their devices create interference to the EM spectrum below 500kc and especially to amplitude modulated types of signals.
  

References:

1. Hazeltine, the Professor - by Harold A. Wheeler, SE-1420 origins and history - published in Radio Age, April 1978

2. Radio Manufacturers of the 1920s, Vol 3 -  RCA and Wireless Specialty Apparatus history - by Alan Douglas 1991

3. Westinghouse Type RB, photo of Type RB - by Alan Douglas - published in Radio Age, November 1982

4. Tropical Radio and Telegraph Co., United Fruit Co., NESCO, ISC, International Radio Telegraph Co. -  Geo. C. Clark "Radioana," Wikipedia and various other online sources

5. "Keeping the Stars and Strips in the Ether" - RCA-Navy relationship, Creation of RCA by General Electric, Purchase of American Marconi by GE -  from Radio Broadcast - June,1922

6. "IP-501-A Manual" - RCA/RMCA - available online

7. "The Radio Manual" - Descriptions and Operating Instructions for SE-143, SE-1420 and IP-501 - by George Sterling, 1st Edition  1928

8. "How to Make Commercial Type Radio Apparatus" by Milton B. Sleeper - No. 2 in a series of booklets on radio equipment published in 1922 by The Norman W. Henley Publishing Co., NYC, NY