Radio Boulevard
Western Historic Radio Museum

Navy Department - Bureau of Ships

Model ATD
 Aircraft Radio Transmitting Equipment

Contractor:  Bendix Radio Division of Bendix Aviation Corporation

SN: 2104 built by: Sparks-Withington Co. (Sparton)

ATD Basics, Mechanical Construction, Electronic Requirements
Using an ART-13 AC Power Supply to Power the ATD
Getting the ATD to work with a 50Z Antenna Load, Series Antenna Capacitors
Operating the ATD "On the Air," The Missing RF Amp Meter Solution
Dynamotor Details, An "Easy-to-Build" 80 Amp Power Supply To Run the Dynamotor
Boosting the ATD Output using the W6MIT Linear Amp

by: Henry Rogers WA7YBS

ATD Components Shown in Artwork

A - ATD Transmitter

A - 200kc -500kc Tuning Module

B - LF Antenna Tuner

C - Dynamotor

D - Pilot's Channel Indicator

E - Pilot's Remote Control

F - Dynamotor Battery Cable

G - Transmitter Power Cable

H - Remote Cable

I - Indicator Cable

B&W Artwork from the ATD Manual

This write-up is a little bit different. All of the repairing, rebuilding and restoration is presented in a "day-by-day, problem-by-problem" journal format that also has included the solutions to the multitude of minor issues encountered. Of course, the ability to easily apply the voltages required at the current levels necessary for proper operation is one of the most difficult aspects of setting up a vintage aircraft transmitter to function effectively in a home environment or ham shack. Though a homebrew ART-13 AC power supply can operate the ATD, I've found that it's also not too difficult to set-up and use the ATD dynamotor to provide the proper voltages at the necessary current levels. However, the dynamotor's 50A+ "instantaneous starting current" can present problems. Fortunately, I found an easy solution and plans are included for an "easy-to-build" 80 AMP +28vdc power supply that can provide all the current necessary for dynamotor operation. Antenna matching solutions are easy to accomplish. There's also the fairly low RF output power that makes reception of the ATD's signal a challenge for many of the mil-rad net participants. How to boost the power output with a linear amplifier is also covered.

U.S. Navy - Bendix Radio Div. of Bendix Aviation Corp. - Model ATD Aircraft Transmitter
 

ATD Transmitters Post-WWII and Today - The total number of ATD transmitters built was probably much less than 5000 (serial numbers might go up to 4000 or so.) Many were never used and were still essentially new in their crates (packed with all their accessories) after WWII ended. Many of these "new in the crate" ATDs were sold surplus after the war. However, the ATD transmitter certainly wasn't a modern design and it wasn't suitable for use by post-WWII airlines like the ART-13 was. Its multitude of tiny-sized knobs and hidden adjustments made "in-flight" retuning impossible.    >>>

USN-Bendix ATD Transmitter CQW-52253 SN: 2104

Today, there seem to be three types of ATD survivors,...the "found in the crate" mint condition transmitters that were kept in NOS condition and were never worked on. These types of transmitters, despite their pristine physical condition, rarely function "out of the box." At the other end of the condition-spectrum are the hacked-up junkers that were the unfortunate victims of the readers (and believers) of the Surplus Conversion Manuals put out by CQ magazine. But, many ATD transmitters, while maybe not mint, are still in pretty good shape. These "less-than-perfect" transmitters haven't been hamster-hacked and they weren't converted into something else that wouldn't function either. The following sections of this write-up are a detailed account of what to expect from, maybe not perfect, but a pretty nice ATD. One that obviously wouldn't work "as-found" but looked like it might be coaxed into becoming a functional transmitter. Obvious problems are that only one of the tuning units matches the main frame serial number (so three tuning units are replacements for some reason,) the RF Amp meter is gone and all of the tubes except the 12SL7GT are gone. All of these clues are indications of a non-working unit that supplied a RF amp meter and some tubes for some other projects but was kept in relatively good condition,...well, except for the usual moving and storage cosmetic problems. So, let's see what it takes to get this relic of early WWII actually producing some RF,...

ATD Basic Design and Construction

The ATD is an aircraft transmitter that was designed to be powered by the aircraft's battery-charger system running the ATD dynamotor. The transmitter's output signal was fed to a relatively short antenna that usually ran from a post in front of the cockpit to the vertical stabilizer (usually a 25 ft "T" antenna.) The transmitter was setup to operate "remotely" by the pilot of a two-seater airplane. The two-seater airplanes at this time had a front-seated pilot and then the second person was seated about eight feet behind the pilot at the rear of the cockpit. The second person in the aircraft could operate the transmitter if deemed necessary by the pilot or if the pilot was incapacitated for some reason. The second person would have to cut the safety wire on the LOCAL-REMOTE switch to allow placing the transmitter in LOCAL. Then the second person could operate the transmitter directly, but normal operation of the ATD was by the pilot only and by using the Remote Control Unit that was mounted by the pilot's seat.

Four channels were available for operation. The multitude of adjustments that were necessary for each channel to operate properly made "pre-flight radio setup" a prerequisite. Since any significant frequency adjustment of any channel required removing the channel's individual Tuning Unit from the main frame for resetting four internal switches followed by retuning the transmitter, any readjustment of settings during the flight wasn't practical and essentially couldn't be accomplished. The manual implies that neither the pilot nor the second person were necessarily "radiomen" but they could "operate" the transmitter within the limitations of the pre-flight setup. The fact that the REMOTE-LOCAL switch was "safety-wired" to REMOTE implies the second person in the airplane wasn't a trained radioman (the manual does refer to this person as "the operator" even though he can't directly operate the transmitter.)

The frequency selection of the four channels was motor-driven based on the position of the channel switch on either the transmitter or its remote. A chain-driven rotating "letter wheel" (on the ATD) would display which channel had been selected. The selection of a channel's tuning module was accomplished by the motor driving a gearbox that slowly rotated a shaft that had four cams. The four cams with "roller tips" on the shaft were spaced at 90º increments and would individually would push down a specific rectangular push-rod for each channel as the shaft slowly rotated. The push-rod had several metal pins (~.25" diameter) that would push down the movable selector contacts on the back of the selected Tuning Unit to connect the various frequency controlling circuits and the antenna matching circuits for the channel selected. Unselected channel contacts were grounded by way of the spring-loading of the contact arms contacting metal grounding pins. The motor-drive used a forward and a reverse winding that was timed to use just a momentary "reverse" connection to stop the motor after the forward winding was disconnected. This allowed precise position stopping at the selected channel with no "over-shoot." There was a manual channel select knob on the right side of the transmitter. If the handle of this knob was folded out, that disengaged the motor drive gearbox and the main shaft could then be rotated using this knob. When finished with the manual adjustment, the knob was folded back, "rocked" slightly and then the manual control being "spring-loaded" would "drop into position" to engage the motor drive gearbox and to be in the correct position displaying the correct channel.    >>>

There are a multitude of relays in the ATD. The sending relay switches the antenna from receiver to transmitter with actuation of the sending key or PTT. The Phone relay selects many of the functions necessary for voice or MCW operation. CW selection places the +1000vdc on the 814 plate and +380vdc on the plates and screens of the other tubes but allows the telegraph key to work the keying line (PTT.) There's another relay that places a capacitor on the PA grid to keep it from oscillating when the TUNE mode is selected (it's switched out with PTT or keying.) There's a connecting strap between the TUNE and OPERATE switches so they will function together. The TUNE switch is isolated since it connects the +1000vdc when OPERATE is selected.

The Grid Current Meter measures the MO plate output by its connection to the PA grid. This meter has a switch that allows it to also read battery voltage (the aircraft battery buss voltage.) The PA plate meter reads the plate current (cathode current) on the 814 tube. The RF Amps (Antenna Current) measures the actual RF current to the antenna (fs=5A.) Power output is normally 50 watts in CW and 40 watts in Phone.

The dynamotor provides +380vdc at 400mA and +1000vdc at 150mA. Input voltage is +28vdc and the current required depends upon the load but could range up to 19 amps in some modes and to certain types of antennas (this is the "up and running" current but the actual "instantaneous starting current" is around 50 amps.) The top cover that allow access to the tubes has an interlock switch that only allows the +28vdc to go to the dynamotor when the ATD lid is closed. The dynamotor also has an interlock on its top cover. The Cannon box connectors on the left side of the transmitter are for the dynamotor, the remote and for the channel indicator (a box with buttons that would protrude out if that channel was selected and would retract if another channel was selected and then that channel's button would protrude out. Both the remote and the indicator were up with the pilot.) The remote was operated by the pilot and had inputs for a mike and a key along with the ability to select channels. No meters or other indicators were on the remote.

The dynamotor runs on the +28vdc aircraft battery buss. The +28vdc battery buss is also routed directly to the transmitter through the dynamotor and ATD power cable. When the ATD is powered up, it routes the +28vdc back to the dynamotor relay via the PTT line to power up the dynamotor to supply the +380vdc and the +1000vdc. CW operation will have the dynamotor running while the transmitter is keyed. In Phone, the PTT turns on the dynamotor for operation.

AC Power Supply Operation - To run the ATD will require +1000vdc at about 150mA, +380vdc at about 400mA and +28vdc at maximum of about 20 amps for the dynamotor (this doesn't include the instantaneous starting current,) but only about 5 amps are required if the +28vdc just powers the transmitter. It's convenient that these voltages are very close to those required by the ART-13 transmitter. This makes operating the ATD using an ART-13 AC power supply a real possibility. The current requirement of 400mA on the +380vdc line might be a problem in some ART-13 power supplies (it depends on the design.) My "Homage a le Valve" ART-13 AC PS provides +1050vdc at 250mA, +420vdc at 250mA and +28vdc at 10A. I'll have to do some slight modifications to the +400vdc supply but whether the ATD actually requires almost half an amp on the +380vdc line will have to be determined when I actually get the transmitter operational. If the +380vdc actually does require 400mA then a separate +380vdc with higher current availability would be required. I do have the HP 713B that could supply +380vdc at 500mA, so that's a possibility,...if it becomes necessary.

ATD Aircraft Transmitter SN: 2104 - Problems and Solutions

This is more-or-less a chronological listing of what it took to get the ATD to actually produce a RF signal into an antenna. Dates are at the end of each paragraph.

The Plate Current Meter had the glass pushed in. This required complete removal of the meter to fix this problem. It's more difficult than it sounds because the ATD right-side panel can't easily be dismounted. Dealing with the nuts and washers that mount the meter requires some special tools. Once the meter was out, the housing and the glass were cleaned. The meter zero mechanism needed to be reassembled and then glued. The retaining ring for the glass had to be installed by pushing it evenly down to be against the backside of the glass. Then Cyno-A glue was sparingly applied to keep the ring in place. The meter was reinstalled. The one nut and washer on the lower inside has to have the washer super-glued to the nut and then, using a special tool that holds the nut/washer, it can be held in place and threaded by turning the screw in the front. The other two nuts are fairly easy to access and remount.  8-17-24

Thumb Screw for Ch.B Osc Adjustment Lock was missing. I found it inside the transmitter during disassembly. Luckily, it just screwed back in place and works correctly.

Missing and Broken Fasteners - Several screws, lock washers and nuts missing. One broken screw on the Antenna-Sending relay board (K-103.) Enough of the threaded portion was left to allow gripping with flush type side cutters to get the piece unthreaded and removed so a new 4-40 BH screw could be installed.  NOTE: I didn't notice until I doing the final assembly and mounting the rear panel that the lower-left corner 6-32 BH screw had been broken off and the remains were deep in the threaded hole. I may fix this later. I don't want to do any drilling, screw extraction and re-tapping with all of the tubes installed.

Unobtainium Power Connector, a Solution that Works - The box connector is a Cannon NK-M8-32S - I assume the mating connector plug is Cannon NK-M8-32P but I can't find any source that has "32" size connectors. Original NOS or Used will have to be found. Until a proper connector can be located, the pins are .125" diameter and the same size as the tube pins on a five pin tube base. A fiber-type five pin tube socket has receptacles that almost surround the tube pins. These can be removed and used for the connection to the socket pins. Then proper size wires can be used for a cable. The pins will have to be insulated. When building the cable, it will have to be sleeved with copper braid for shielding. This cable will be six feet long so the PS (or dynamotor) can set on the floor if it needs to. UPDATE: Allpoints supplies a very nice push-on female wire connector that's for .125" diameter male pins. Wire solders to the rear of the pin and there's a wrap-around strap to support the wire/insulation. These are really perfect for this application. For some reason, these quality connectors are impossible to find locally but can be ordered online from Allpoints, pn 85-1075, at around $3.80 each.

View with Rear Cover Removed showing the Tubes

Homage a le Valve - ART-13 AC PS uses 866A and 5U4GB Rectifiers

Tested the Two Audio Transformers - I used the schematic to determine where to access the primaries and secondaries for each transformer. Both the audio driver transformer and the modulation transformer tested okay. 8-18-24

Cleaned All of the Relay Contacts and the Contacts in the Main Frame for the Tuning Units - I used DeOxit applied with a saturated piece of paper that was drawn through the relay contacts to clean them. The stationary Tuning Unit contacts were cleaned with DeOxit applied with a small paint brush and then wiped with a paper towel (later these Tuning Unit points were cleaned more aggressively.)  8-18-24

Cleaned and Inspected Channels A through D Tuning Units - Mildly dirty, a few broken or missing screws. Slightly bent sheet metal on Ch. D air variable-C but it seems to have been that way since the original assembly. There's a flex-coupler on the shafts that compensates for the misalignment. Originally, the ATD came with a 540kc-1500kc module, a 1500kc-3000kc module and two 3000kc-9050kc modules installed. Mine has two 540kc-1500kc modules and is missing the 1500kc-3000kc module. One of the 540kc-1500kc Tuning Units has the only serial number that matches the main frame serial number.

Channel C Tuning Unit - Broken screw head on rear bottom insulator panel (6-32 BH.) Removed the broken screw by removing the rear nut and washer so it could be pushed out of the hole. Installed new 6-32BH machine screw and installed the washer and nut.

ATD with the Bottom Cover Removed

The Motor Drive Shaft and Cams with Roller Tips for Changing Channels

Motor Drive Channel Select - Read the Manual - I've re-read the manual several times and no where does it say that the motor runs in reverse if a "lower" letter is selected. I checked the sequence of the forward and reverse contacts and it looks like it does exactly what's described in the manual. The motor-drive is working great and stops perfectly on whatever selected channel is set. I'm wondering if the "reverse" operation on "lower" letters (an assumption on my part) isn't really what the "reverse" is for. I now think that the "reverse" motor winding actually seems to be for "stopping" the motor exactly in the correct position for the channel selected with no "over-shoot."   8-20-24

Cleaned Antenna-side panels, remounted and resoldered Antenna buss wire. Until I get the RF Amp meter from Mike 'MS, I'm just going to connect the RF output directly to K-103, the sending/antenna relay. That way I can proceed with testing the ATD. The RAJAH bakelite spark plug terminal push-on connectors arrived today. These will be used to connect the antenna and ground to the ATD.  8-22-24

Side showing Ant-Rcvr-Gnd Mount

ATD Dynamotor - TYPE DMDFX618 sn: 260453
Mfg. by: Continental Electric Co., Inc.

ATD Dynamotor Arrives - I found an excellent condition (NOS, actually) ATD dynamotor for $70. It arrived today. I don't plan on running the ATD on the dynamotor just yet. If and when I move the ATD out to the shop, that's where I have the large PP-1104-C power supplies (three of them) for running high-current devices. I'll have to either modify the power cable I just made or build another. But first, the ATD needs to be running correctly on the ART/PS and operated "on the air" from upstairs. Before I actually used the dynamotor I would have to "service" it. After all, the grease in the bearings is over 80 years old.   8-23-24   Well, that plan changed,...read Dynamotor section further down.

More ART/PS Changes - I checked the schematic and updates that I had made to this ART/PS a few years ago and found that I had changed the +400vdc to a pi-network filter to up the voltage and it was then running about +420vdc, too much for the ATD. I decided to put the +400vdc back to a similar configuration that I had before but without the input capacitor, in other words, a choke-input with dual filter chokes. This should produce about +380vdc. The choke input filtering gives better stability and at least a 10% reduction in output voltage. Test to confirm.  I also brought in from the shop a roll-around small furniture dolly in order to have any easy way to move this ART/PS that weighs about 80 pounds. 8-24-24

+28vdc "ON" Relay - In looking at the ART/PS, the wire from the +28vdc "ON" relay (ART-13 pin 7) that connects to chassis-gnd to power the relay is the next terminal adjacent to the chassis-gnd terminal. Rather than have a second jumper, I just moved the ring lug over to the chassis-gnd terminal to provide the ground return for the +28vdc "ON" relay. Now there's only one jumper and that connects -HV to ground (ART-13 pin 2.)  8-25-24

Set-up and Operational Test - The manual has a step-by-step procedure for testing and set-up. This is probably the easiest way to find any additional faults. I had to move the ART/PS up onto a small table next to the test bench since I really couldn't see the output voltage meters or the indicator lamps with it on the floor. Out of the cabinet it probably only weighs about 65 pounds. 8-26-24

Throttle Switch and PTT Line Problems - The PTT line and the Throttle Switch wouldn't "lock" the sending relay K-103 in the transmit position. This problem was caused by K-101A on the Phone Relay having dirty contacts. I used DeOxit soaked paper pulled through the contacts to clean them. Then the PTT and Throttle Switch both worked correctly.  8-26-24

Side View showing Motor Drive and K101 Phone Relay

540kc-1500kc Tuning Unit showing setup switches inside

More Testing Reveals Another Problem - The +380vdc under load measures +360vdc which is close enough. VT-150 glows purple when transmitter is operating. So far all testing is in the "TUNE" mode which prevents the +1000vdc from going to the 814 plate. I setup one of the 3000kc-9050kc modules for 4000kc operation. I connected a 50Z dummy load to the ANTENNA-GND terminals. There are four switches inside each of the four modules that have to be set correctly and then there are six front panel switches or controls have to be set correctly for the frequency of operation on each module. The ATD was set for CW operation. When the TEST KEY is switched, some PA grid current should show, however, the meter actually went negative. By tuning the MO PLATE, I could just get the meter to read "0." I happened to look at the 814 when I pressed the TEST KEY and the bottom half of the tube turned purple inside. This is a sure sign of a "gassy" tube, so no wonder the PA GRID current wasn't measuring as expected. I thought I had an 814 in my tube stock but I couldn't find it (if I ever had it.) I had ordered two of the cheapest 814s off of eBay. Neither of the tubes had been tested but the sellers thought the tubes were NOS. The first 814 had an open filament (got my money back on that one.) The second tube didn't show much emission in the TV-7 and did give a slight indication of being gassy but I thought it might work in the ATD (I didn't ask for a refund since a couple of weeks had passed before I actually tested the tube in the transmitter.) This second 814 was in the original box with the original wrapping and original paperwork,...naturally the seller thought the tube was NOS so it wasn't tested. But, it's gassy, and the purple glow was only with the +360vdc screen voltage applied (wonder what it would have done with the +1000vdc plate voltage applied?) The only way to proceed is to buy tubes that are tested and guaranteed. These two "cheapies" were a waste of time. I ordered another 814 that the seller provided the TV-7 test data information on. We'll see what happens with this tube when it arrives. Out of curiosity, I'm sure the "cheap-o" prices might be of interest, right? The open fil 814 was $15 and the second gassy 814 was $18. The tested 814 was $39. So, luckily, the 814 isn't an expensive tube but I wasted a lot of time and that's what was aggravating.    8-26-24

The New 814 - The new 814 arrived on Friday 8-30-24. I tested it in the TV-7 and this one actually tested good. I couldn't get the old 814 out of the ATD unless I took the rear cover off. Luckily, I had only put about six screws in since I thought I might be taking it off again. With the new 814 I now had about 15mA of PA grid current that would easily peak with the MO Plate control as described in the test procedure. Next was to go to OPERATE. I had about 80mA of PA current showing but the Plate tuning brought that down to 40mA at resonance. I tried several adjustments but it acted like the antenna wasn't connected but the dummy load RF meter did show a few watts of output. I tried connecting two dummy loads in parallel to have about 25Z load, this didn't help, still about 30mA to 40mA at resonance. I checked the manual procedure and it indicated that without an antenna the PA current would resonate at 30mA, which it did. I then found in the front part of the manual that the expected antenna was a 25 ft "T" antenna and the antenna resistance at 3mc was expected to be just 1.3 ohms with a capacitance of 80pf. The 50Z dummy load (or 25Z in parallel) must look like there's no antenna connected. But, reading a little further, there's a section on loading "abnormal antennas" that indicates that the series capacitor can be switched out or the taps on the antenna L can be changed to allow matching unexpected antenna impedances.  8-30-24

PHONE Operation and CW "On the Air" with Collinear Array on Harmonics - First I tried the Sidetone. I used 600Z phones but I didn't hear anything out of either jack. Next, I switched to PHONE and plugged in a Shure 102C carbon mike. I've used this mike many times and it has a good response. I could just barely tell that the PA was being modulated. I could see the plate current meter move a little. I had the signal (still on the dummy load) tuned in on the bench monitor receiver. I could hear some modulation but it was probably only 30%, barely detectable. The +380vdc is running at +340vdc under load. I didn't notice any change in the voltage as I spoke into the mike. The manual indicates that the +LV can be anywhere from +300vdc to +400vdc and since the dynamotor would vary in speed with the charging rate and engine speed, it would be expected that the dynamotor voltage would vary some. I tried connecting the ATD to the Collinear Array through the Viking Matchbox tuner. The tuner didn't show any change in the very high SWR. I added an auxiliary variable condenser on the Antenna output to ground (like the ART-13 uses) and I ended up switching the tuner to 40M. Now, I could get the SWR down to 1:1 and the PA current at 100mA. That gave me 35 watts to the antenna. I think if the screen voltage on the 814 was up to +380vdc or so, I'd be able to get more PA current and output. My concern though is that I've tuned the output network of the ATD to a harmonic of 3.974mc which would be 7.948mc and that's how I can get the tuner to achieve a 1:1 SWR on 40M but not on 80M.  8-31-24

Experimenting with Various Antenna Coupling Capacitors - Since I was pretty sure that I had the ATD antenna coupling circuit tuned to 7.948mc instead of 3.974mc, I set all of the internal switches back to where they should be (G, H and J on 2 and K on 1.) Then, figuring that I had reduced the L in the module and got the loading to somewhat work (although on a harmonic,) the Collinear Array and Viking Matchbox must look like a lot of inductance until resonated and by adding capacitance in series, that might work. By switching K to 1, that added a series C already but it wasn't enough for a 50Z load. I tried 100pf first and this allowed the ATD to get kind of close to loading correctly but it required too much L that the module didn't have. I added another 100pf in series to have 50pf in series. This worked very well although I had to switch E to position 4 instead of 5. I could get a little over 100mA of PA plate current. I added another 50pf in series for 25pf. The results were about the same except switch E had to be in position 3. This switch E was adding L to the Antenna Loading which seemed to indicate I was close to finding a range of series C antenna coupling that worked. I think about 60pf or so would allow switch E to remain on 5 and I'd be able to get over 100mA of PA Plate current (later I was to discover that 100mA is way too much plate current.) I have to look through my high voltage capacitors to find a combination that will give me 60pf. OR, I have a box of NOS transmitting type air variables that are very small capacitance, probably 10pf unmeshed to 100pf meshed. Using one of those would allow "dialing in" what C works best.   9-1-24

Showing the electrolytic C102 Carbon Mike bias filter
The Sending Relay K103 is shown to the left

37pf of series C for 50Z antenna with RAJAH connectors

More Antenna Capacitor Testing - I tried the 100pf max air variable but the plates were too closely spaced and it arced at resonance. I have many other wide spaced air variables but the fixed high voltage caps are much easier to use. I tried 60pf and that was too much. I ultimately ended up with 37pf with the E switch on 3. I found that maximum output power doesn't happen with maximum PA plate current. At 110mA, I had about 25 watts output but at about 80mA I had 40 watts output. The SWR at the Matchbox is 1:1 so reflected power is zero. I suspect that when I raise the +340vdc (that is what it measures at 40 watts output) up to at least +380vdc, I should be able to have better efficiency in the 814 with higher screen voltage and I should be able to load up to 50 watts output on CW.   9-2-24

The ART/PS +LV Mod that Worked Best - First I tried connecting the +LV filter as a pi-network but the voltage was too high even under load (+420vdc.) Also, I had almost 20mA of PA grid current because of the high plate and screen voltages. Next, I connected the +LV filter as a single choke with output filter capacitor. Now, I was back to +340vdc under load. I listened to the signal on the monitor receiver and there really wasn't any change in the hum level. Then I thought about the capacitor. I had 20uf made up of two series 20uf caps at 10uf and a second series pair in parallel giving 20uf total. I had some 100uf 450vdc electrolytics that two in series would provide 50uf of capacitance. I added 750K balancing resistors to even out the voltage drop on the series electrolytics. With this hook-up, I had a consistent +360vdc under load in CW.  9-2-24

Using a D-104 Mike? - Why not? I set the mic switch to Magnetic (meaning dynamic) which is a 250Z input (same as the ART-13.) The D-104 is on an amplified base so the Z is much lower than a crystal mike and the gain can be adjusted as needed with the base's gain control. No problem in modulating the ATD. It sounded very good in the monitor receiver. While I had access to the Mic switch, I also set the Sidetone volume down to 4.

ATD Reassembly -  I installed the second 3000kc-9050kc module and set it up on CH. C to the same 3.974mc and made sure it loaded and performed the same as CH. D. I then installed the two 550kc to 1500kc modules but since these really aren't usable "on the air" I didn't do any setup on them. They are in channels A and B. I installed all of the panels and all of the screws with lock washers.

More Antenna Capacitor Testing - I got to thinking that I had some doorknob capacitors that might work nicely for antenna caps. I found two 50pf, one 100pf and several others that were higher values that couldn't be used. By using the 100pf in series with one 50pf, I'd have 37pf and that should work very well. I used the RAJAH connectors and made one end of the capacitors able to plug into the ANTENNA terminal on the ATD using a short flex cable made out of copper braid and the other end of the caps were soldered to the coax center conductor of the ATD coaxial cable. The shield of the coaxial cable also had a RAJAH connector for the GND terminal. I then connected this cap-coaxial stub to a 50ft coaxial cable to run into the ham shack to connect to the Johnson Matchbox and the Collinear Array. This hookup allowed me to use the Drake W-4 wattmeter and the modulation monitor oscilloscope. With careful tuning, I found that the best setting was at 80mA of Plate current and that showed 48 watts on the wattmeter with a 1:1 SWR.

ATD Works on the Bench. Note the "dummy" ANTENNA CURRENT meter

Operating the ATD "On the Air"

The ATD powered up fine although there isn't any visual indication that the transmitter is "ON." The BATT V switch can be pressed and it should read +28vdc when the ATD is "ON." I was on CW so I switched on the high voltage at the PS. Pressing the KEY, I had about 85mA of PA Plate current. I checked the wattmeter and it read 55 watts. I think because the +HV is actually running about +1100vdc instead of +1000vdc (only 10% high) that's the reason that I have to load to a lower PA current. I reduced COUPLING slightly and dipped the Plate, I still had 55 watts. I reduced the ANT TUNING and dipped the Plate, now I had 50 watts at 75mA of Plate current. I went to PHONE and I connected the amplified D-104. Pressing the PTT, I still had 50 watts output. I reduced the COUPLING slightly and the ANT TUNING slightly and the power output dropped to 40 watts. I looked at the monitor scope as I talked into the mike. Lots of modulation but I don't seem to be going all the way down to cut-off. Negative modulation looks like about 80% maybe. Watching the +360vdc, it drops significantly with the voice peaks,...maybe down to +320vdc. Obviously, the current required for the modulator to really achieve cut-off is more than the ART/PS +LV can supply. I may bring in the HP713B power supply that can provide a solid +380vdc at 500mA and test the ATD in PHONE then. I would then have to do a few mods to the +400vdc supply in the ART/PS to get the current available up to 400mA or more.

More Current Availability for the +380vdc Needed - Even though modulation isn't as potent as it could be, I think with the D-104 mike, the ATD will sound fine. After all, it's just the first "on the air" test coming up. The ART/PS upgrade can be another project in a week or two. I have a hefty 400vac CT transformer that must be good for at least 500mA. It measures as a 5.5" cube and has no other windings other than the 400vac CT and the primary. I'd have to look for a 500mA choke but I should be able to find one. I do have room on the ART/PS chassis if I rearrange some of the components. Not too much work - well, certainly not as much as building a complete PS. But, before I do that, I have to bring in the HP713B and verify that 500mA of available current will cure the wobbling +360vdc supply and allow 100% modulation.

Arcing in the Unused Modules - I read in the manual about the unused modules causing problems if they are tuned to harmonics of the frequency being used. The cure is to retune them to a different frequency. I never tuned either of the 540kc-1500kc modules. So, I'll start by tuning one to 600kc and the other to 1100kc. Neither are harmonics to each other and neither are harmonics to 3974kc. I think I'll retune CH C to a different frequency than CH D. Maybe I'll set it up for 40M or easier would be 3995kc, an informal mil-rad net.

When looking a little closer at one of the AM-BC tuning modules I noticed that four screws were missing. Two were completely gone and the other two had the screw head "popped off." These appear to be 5-32 screws but a 6-32FH fits fine and these screws, washers and nuts are only for the Garolite mounts for two of the coils. I installed the four 6-32FH screws using lock washers and nuts.  9-4-24

I thoroughly cleaned the contacts and the levers plus shot some DeOxit into the heads of the levers. I used a brass bristle brush and some DeOxit on a paper towel. I also cleaned the switch contacts G,H, J and K. Before installing the modules, I set one for 600kc and the other one for 1100kc. I set CH D for 3995kc and CH C is set to 3974kc. I tested the ATD and now there's no arcing.

I had KØDWC (located about 2 miles away) listen to the transmitted PHONE signal from the ATD. I could also hear the signal over the telephone although there's a propagation delay of about half of a second that sounds like an echo. Other than a little feedback over the phone and the delay, the audio sounded good and Chuck also thought the ATD sounded good. I'll be giving the "ATD debut" on Sunday's (9-8-24) Nevada Mil-Rad Net on 3974kc at 0700hrs    9-5-24

Second, accessing and removing C117 is made impossibly difficult due to the shield around the MO tube. With the 814 removed, one end of C117 is accessible but the other end is behind the MO shield. Although the shield might be removable, the mounting screws have washers and nuts that are covered by several MO components under the tube shelf. The value of C117 is .01uf and it's the standard "postage stamp style" cap with the yellowish-brown square body and the color-coded dots. I had several of these in the parts box. The color-code is probably the old RETMA code and has brown-black-black with a multiplier of red which equals 10,000pf or .01uf. Then there are two green dots for 5% and 500vdc rating. I found several .01uf square-package capacitors. I tested their working voltage up to +340vdc (max that the bench supply can achieve) and all caps handled the voltage fine. I chose the one that looked closest to the original. I lifted one end of the CH A MO plate load 300 ohm 1W CC resistor R148 and found that it too was cracked from overheating due to the shorted C117. I found some old style IRC 1W CC that were 390 ohm which is probably close enough. I couldn't get the soldering iron in behind the MO tube shield. I was going to take out the shield by removing the six screws, washers and nuts but I couldn't budge the screws (and I didn't want to break the screw heads off.) The nuts weren't accessible at all. I went back to trying to remove C117 by breaking one of the leads using a "soldering aid" tool but during the process, the solder lug broke instead. I had to use a different ground by adding a solder lug to a ground screw that was nearby. The parts were installed and they look like an original placement using original parts. I installed one of the 3000kc to 9050kc tuning units in CH D slot and applied power. I had 13mA of PA grid current, 90mA of PA Plate current and 50 watts output power. The +380vdc was +350vdc under load.

Next, I installed the other 3000kc to 9050kc tuning unit and again I had 50 watts output with about 13mA of PA grid current. I installed both 540kc to 1500kc tuning units and then I had what appeared to be a short with no PA grid current. I pulled the BC tuning units and then the ATD went back to having full output. I plugged in one BC tuning unit at a time to determine which one was causing the problem. It was the BC tuning unit I had tuned to 1100kc. The problem is in the MO circuit of the tuning unit and that involves one tapped coil, a five-position switch, three capacitors and some wires. By selecting various switch positions 1 through 5, each of the three capacitors can be eliminated as the problem. That would leave the tapped coil or the wires. Since the rear lever switch shorts out the coil when the tuning unit isn't selected, it would seem that the coil could be eliminated. Since the AM-BC tuning units are virtually worthless and could never be used because their frequency of operation is entirely within the AM-BC band, perhaps the easiest approach is to remove P601 (a banana plug) which is the source of the +380vdc for the tuning unit. This, essentially, would eliminate the problem. The defective BC tuning unit will be replaced as soon as I find a 1500kc to 3000kc tuning unit, which would be usable on the 160M band.

NOTE: When installing the "disconnected" BC tuning unit into the main frame, I noticed a very slight change in the "tune and load." It shows as a 5mA reduction in PA plate current. The load on the +380vdc doesn't change. A slight "touch-up" on the tuning of the two 3000kc to 9050kc modules was required. I think the proximity of any of the tuning units to the RF output buss wiring probably slightly changes the stray capacitance to ground and very slightly changes the "tune and load" settings. Once all tuning units are installed, the final "touch-up" seems to be consistent and remains at those settings.

Luckily, the TA-12 meter is a Weston 507 and the ART-13 meter is a Weston 507, so the scales are interchangeable. The scale swap was easily accomplished although the TA-12 meter needle needed to be white instead of black. I used a Sharpie White Paint Pen which is a very thin paint that covered the needle perfectly in one easily applied thin coat. The needle stops were missing on the TA-12 meter but present on the ART-13 meter. Essentially, between the two meters I made one black scale, 5 Amp RF current meter for the ATD.

The top cover on the ATD had to be dismounted to have access to the RF Amp meter. Next was some work on the spacer which, of course, was for a TA-12. It wouldn't fit into the ATD without some involved modifications. The right side of the spacer had to be cut in order to have clearance for the metal frame's right side shielding of the ATD. This was accomplished carefully with a hacksaw followed by some dressing down with a file. This cut also was necessary for the meter flange. Then the left side had to have .250" of relief depth (removing spacer material) from about 200º up to about 350º for clearance of the ATD metal framework. Finally, about .190" of relief was necessary at the top (almost down to the threaded hole) and additional .250" relief depth from 5º to 20º to clear the upper framework. Once these cuts were made, the spacer fit correctly up flush with the back of the panel. The rebuilt meter was mounted to the spacer and then the entire assembly was mounted to the front panel using the original meter "flange bezel" the rear portion of which fits through the inside of the spacer and hides the spacer when viewed from the front through the bezel glass.

RF Amp meter hook-up required a small section of 12 gauge buss wire because the original meter had been "cut out" leaving the existing buss wire too short to reach the meter. I used a crimp splice (with the plastic removed) and soldered it to make a junction between the original buss wire and the new section going to the meter. The original output buss wire I had connected to the sending relay that then switched to the ANTENNA terminal when transmitting. Now this buss wire had be connected to the meter. Then a new 12 gauge wire had to be run from the other meter terminal to the sending relay. That completed the hook-up.

Operation - With a 50Z antenna load at a 1:1 SWR and only about 45 watts input, the Antenna Current shows about .4 amps, so the meter needle doesn't move very much. With a very low impedance antenna, such as an electrically short vertical, the current would read much higher. Also, the TA-12 white scale had a different projection than the black ART-13 scale so the actual accuracy of this RF Amp meter is compromised (most Antenna Current meters were just used a "peak output" indicators and not for calculating power output since the antenna impedance was probably unknown.) I noticed that with the RF Amp meter installed inline with the RF output now that some slight readjustment of the tuning modules was necessary. Not totally unexpected and the power output is still at 45 watts to 50 watts (measured with an external but inline wattmeter.)

The RF Amp meter is now recessed back about one inch behind the front meter bezel glass. The genuine ATD meter had "RF AMPERES" on the meter scale instead of "ANTENNA CURRENT" that the ART-13 meter scale has. The projection of the scale is also different. With a 50Z antenna and only 45 watts output, the RF current shown on the meter only reads about .4 amps but, with the different scale, it's not an accurate indication anyway.

THIS SOUNDS LIKE A LOT OF WORK! - I'm having second thoughts about this involved of a modification to the Homage a le Valve ART-13 power supply. So, for now,...further modifying the Homage a le Valve ART-13 PS has been halted. Now I'm going to take a look at the possibility of dynamotor operation,... 

Servicing the ATD Dynamotor
Constructing an "Easy-to-Build" 80 Amp +28vdc Power Supply
Operating the ATD on Dynamotor Power

With all of the modifications required for the "Homage a le Valve" ART/PS, sometimes it seems that it would be easier to just use the dynamotor. The 27 amp +27vdc Lambda power supply doesn't provide enough current to even start the dynamotor. Though the manual indicates that about 20 amps is required for ATD-phone operation, this is "running current" - not "instantaneous starting current" - which obviously exceeds the capabilities of the 27 amp Lambda. However, there's an old trick of connecting similar power supplies in parallel to increase their current capabilities. I connected TWO 13 amp Meanwell +27vdc switchers in parallel with the 27 amp Lambda. I set all three PS outputs for +27vdc +/- 0.2vdc. In theory, I should have 53 Amps available. Will this actually work? Read on,...

The end-bells on this dynamotor still have the mounting screws "safety-wired" and it's unfortunate that the wire has to be removed in order to dismount the end-bells to have access to the bearings, brushes and commutators. With the end-bells off, I could use the fan to manually rotate the armature to see if it would move and how much "drag" there was. The armature did move and the drag was considerable.

Component box inspection turned up a leaky oil-filled capacitor. This was physically "leaking oil" not current leakage. Although it looked like a lot of oil it really wasn't. The residue was cleaned up with a Q-tip. This "weeping" of oil is common and usually isn't a problem if it's just the "weeping" type of leakage. The capacitor will have to be monitored from time to time to see how much (if any) oil leaks out. Everything else in the component box looked in good condition. All spare fuses and tools were present.

Pulled all of the brushes. These were placed on a white sheet of paper in the proper orientation and placement for reassembly. Pulled the fan off of the shaft to allow access to the bearings and motor-side commutator. Pulled the bearing covers on both ends. Dried grease was obvious. I used WD-40 as a solvent to loosen and remove the old grease. I worked the WD-40 into the bearings on both sides by rotating the armature. At first, with the dried grease, the shaft was moderately difficult to turn and wouldn't "spin." After the WD-40 soaking, the armature spins easily. I let the WD-40 soak in the bearings all night.

ATD Dynamotor - TYPE DMDFX618 sn: 260453
Mfg. by: Continental Electric Co., Inc.

A Tiny Power Supply for Dynamotor Operation - To power up the dynamotor requires at least 45 amps of starting current. I tried 40 amps and the dynamotor pulses, the relay chatters and the armature slowly rolls but never increases speed. At 53 amps the dynamotor starts right up and gets to full speed in about a half-second. Actually, these switchers will supply even more current "peak" for about ten seconds which is more than enough time to start up the dynamotor. The "peak" current available is about 65 amps. I used an old ART-13 dynamotor battery cable that I modified by reworking the connector. The ART-13 dynamotor uses pin 2 for +28vdc input while the ATD dynamotor uses pin 3 for the +28vdc input. I had to simulate the ATD PTT that "turns on" the dynamotor. For this I used two test leads,...one for +27vdc going to pin 1 and then ground going to pin 4. This connection actuates the dynamotor relay and starts the unit. I measured the voltage output with no load and had about +1050vdc on pin 8 and about +405vdc on pin 5.

The test setup is shown to the right. I found the two spare Meanwell 24vdc 13A power supplies out in the shop. They're connected in parallel using 16 gauge wire to provide 26 amps. The Lambda PS is to the far right and it's connected in parallel to the Meanwell combo. The Lambda provides 27 amps. All three supplies were set to +27.02vdc (this was the highest voltage that one of the Meanwell would adjust to, so it determined the voltage setting for the other two supplies.) The output of the Lambda has the battery-type cable that has the ATD-Dynamotor connector on the other end (this cable is also shielded so it doesn't radiate any RFI.) Since the output of the +HV is +1000vdc, I couldn't use the Fluke DDM, I had to use the Triplett VOM to measure that voltage. 

I used a rubber mallet and a wooden block to remove a dent in one of the end bells. Then the end bells were touched-up with black acrylic paint and then installed. This completed the dynamotor clean-up and servicing. Note,...this is one LOUD dynamotor (like a big shop-vac) I was worried about the "screaming fan" on the Lambda PS,...I can't even hear it when the dynamotor is running.

Here's the "test set-up" for the ATD Dynamotor. The parallel switcher-type power supplies provide 65 amps peak at +27vdc, more than enough current to handle the "instantaneous starting" current to get the dynamotor spinning quickly (with "no load.")

Construction of an 80 Amp +28vdc Power Supply That's Physically the Same Size as the Dynamotor - When the new Lambda power supplies arrived, I discovered that although they had the same specifications, they were longer in length and not as wide as the old 27A Lambda. One letter in the Part Number made the difference. It doesn't matter as long as they all can provide 27A. I tested these new supplies and they work fine. I had planned on using a small BUD Industries cabinet that was NOS condition. It measured 12"W x 8"H x 9"D and it had an unused aluminum chassis that fit inside. However, with the different dimensions of the two new supplies, this BUD cabinet is too small. But, I have another unused cabinet that measures 8"H x 14"W x 9"D and it also includes a chassis. But, thinking about the power supplies and their fans and the cooling,...why use a cabinet? The power supplies can just mount on top of the chassis. I had thought that due to the noise of the dynamotor and the power supplies, I'd place both units under the desk. There's plenty of space and lots of air available. The location would have the direct noise blocked, the cables are long enough, etc., so just a chassis for the PS should be easy and will work fine. I plan on using 14 gauge wire for the AC input connections and 10 gauge for the +27vdc 80A output. As mentioned above, this high-current is only "momentary" but I want to make sure that the IR drop is as low as possible and that's achieved with large gauge wiring. The normal "running" current demand will be about 20A, so I'll have plenty of "head room" and that should allow AM modulation voice peaks to not affect the +380vdc very much.
 

I made my own terminal blocks out of .250" thick delrin. Delrin is a type of nylon that is very strong and heat resistant. I drilled and tapped holes in one block for 4-40 brass screws. The holes were countersunk to allow the screw heads to be flush with the surface when installed. Then a second delrin block was used for the insulated base mount. This allowed the terminal block to be bolted to the chassis and the brass screw heads were insulated from the chassis by the delrin base. The 14 gauge power cord was routed into the chassis at the side and the Line, Neutral and Ground wires soldered to the ends of the three brass screws of the terminal block (the ends were .750" long.) Then three additional 14 gauge wires were soldered to the Line and the Neutral terminals and these routed up through chassis holes to the AC input to the three power supplies. These chassis holes had rubber grommets installed.

DC Output Terminal Block Inside Chassis - the studs are 1/4x20 brass and the wires are 10ga.

AC Input Terminal Block Inside Chassis

Since the Lambda power supply chassis are all mounted directly to the aluminum chassis and the Ground terminal on each Lambda power supply is connected to the power supply chassis, the individual Ground terminals on each power supply don't have to be routed to the AC ground wire terminal. But, the AC power cord Ground wire is connected directly to chassis in two places one of which is a lug under one of the Lambda power supplies mounting screws. The AC input to each power supply uses a soldered ring lug to connect the 14 gauge wires to Line and Neutral. There isn't a power switch or fuse in the AC input line. The AC line "bounce" is very noticeable when powering up the dynamotor so a switch and fuse would just limit the available AC line current somewhat. The 80A PS would only be plugged in when it's being used.

The DC output of each Lambda was then adjusted to +28.0vdc BEFORE the three were connected in parallel. I tried to get the output voltages exactly the same from each supply for equal distribution of the current carrying ability (within +/- .002vdc.) The DC output terminal block was made from two pieces of .25" thick delrin with 1/4x20 brass studs and brass nuts and washers to act as the high current output connections. The clearance holes through the chassis for the DC terminal block studs were .750" in diameter. The 10 gauge wires were soldered directly to the back end of the DC output studs. The power supply end of the 10 gauge wires had ring lugs soldered on and then these were attached to the PS output terminal strip. The wires were routed through the chassis by way of grommet-lined holes.
 

With the completion of the wiring, I connected the ATD dynamotor using the shielded ATD dynamotor cable. Pin 1 has to connect to +28vdc and pin 4 is connected to ground to energize the dynamotor relay. Start up was immediate with no hesitation and the armature got up to speed in about 1 second. Switching noise is always a concern with these types of power supplies. To keep the RFI as low as possible the AC input and the DC output were bypassed with .05uf capacitors. The DC cable to the dynamotor is shielded and the power cable from the dynamotor output to the ATD is also a shielded cable. Each power supply is in a metal shielded case that is mounted directly to the PS chassis and the chassis is connected to the AC house ground. I switched on the Siemens E311 receiver tuned to 3.9mc and using a 50ft wire on the floor as a "noise pick up" antenna. The power supply noise wasn't noticeable (not above the ambient noise level.) The starting of the dynamotor is quite a load, so the receiver reacted to the momentary AC line bounce but when the dynamotor was up to speed no noise was heard. NOTE: It's probably noticeable that I didn't use the standard "black-white-green" color code for the Line-Neutral-Ground wires. The only 14 gauge stranded wire I had on-hand was green and red, so that's what I used. The 10 gauge DC wires are red for + and black for -, which is more or less standard. Also, note the labels on the power supplies showing the "CE" certification for RFI noise reduction.

Rear View of 80A-PS showing the wiring to the 3 Lambdas

Front View of the 80A-PS showing the DC Output terminals and Heavy-duty AC power cord (14-3 conductors)

In either case, the RFI noise didn't change the S-meter reading reacting to the ambient noise and was only just barely aurally detectable. The receiving antenna wire was in the same room as the dynamotor and power supply. With an outdoor antenna I don't think any noise will be heard in the receiver. In receive, only the power supply is running. When going to transmit, the receiver is disconnected from the antenna and put in standby so no noise would be heard. Only switching power supply noise is on at the same time as the receiver is in operation.   The Ultimate Test for the 80A-PS: Oct 7, 2024 - As an "ultimate test" of the 80A-PS's capability, I carried it out to the shop (with just one hand, of course) and I then connected up the GRC-19 transmitter/receiver to the 80A-PS. The GRC-19 is a T-195A transmitter with a built-in +LV dynamotor, a rotating AC generator and, since it's the A version, it has the DC to DC converter/PS replacement for the +HV dynamotor and, in addition, it has three blowers to keep the three 4X150D tubes cool. The T-195A draws about 30 amps running and the R-392 adds another 3 amps. The starting current momentarily pegs the PP-1104-C amp meter (probably some meter-needle "over-shoot") for an instant but there's no hesitation in power-up. The GRC-19 has the highest DC current requirements of any device that I have, so it's a good test for the 80A-PS. The little 80A-PS powered-up the GRC-19 with no hesitation at all. After a short warm-up, I pressed the TEST KEY. I had 125 watts output to the 130' Inv-Vee antenna (shop antenna.) No voltage bounce, just pure DC when transmitting VOICE or working the TEST KEY. The 80A-PS is equal to the PP-1104-C in providing +28vdc at a high current level. And, it only weighs about 15 pounds compared to the 100 pounds of the PP-1104-C. A Gladding & Keystone contract PP-1104-C is shown to the right. These were originally part of a battery charging system used by the military. The power supply can be set to 12vdc at 100 amps or for 24vdc at 50 amps by how the four small studs (between the two main output studs) are connected together using supplied jumper straps. The adjustment knob in the center of the panel is a stepped-switch and you can't adjust the output voltage with the "1104" turned ON. Set first, power up to check voltage, power down to reset adjustment, if necessary - a real pain. Also, the "1104" will operate much better and can supply its rated current if it's powered by 230vac input. They can operate on 115vac at reduced efficiency.

The 100 pound PP-1104-C

Running the ATD on the Dynamotor - The end of the ATD power cable (that had connected to the ART-13 AC PS) had to be modified to use plug-in wire sockets since I don't have an original connector. I removed the ATD cable from the ART-PS. I then clipped off the ring lugs and cut the six wires all to the same length. I salvaged the receptacles from an old six pin fiber board tube socket to make suitable push-on female pins for the cable. The connections are easy for the dynamotor to ATD cable since both box connectors are identical and have the same connections, that is, pin 1 to pin 1, pin 2 to pin 2, etc., the colors of the wires can be used for reference. Also, in this cable two wires are 14 gauge for the +28vdc in and the Chassis-Gnd. The other wires are 16 gauge for PTT, Dynamotor Relay return, +380vdc and +1000vdc. The wire push-on sockets were covered with rubber tubing for insulation. The shield of the cable is connected to the chassis of the ATD on one end and to the Dynamotor housing on the other end.

Since the ATD Dynamotor sounds like a very large shop-vac when running and the 80 amp power supply has three fans running, both of these units were placed under the operating desk. The cable is long enough and there's plenty of room under the desk. I did this the last time I ran a large dynamotor in the upstairs shack (the RU-16/GF-11 set up) and it really does quiet-down the operation.

As mentioned, I had to modify the ART-13 dynamotor cable to work exclusively with the ATD dynamotor. I have another ART-13 dynamotor cable, so changing this one to an exclusive ATD dynamotor cable wasn't a problem. Incidentally, the two large wires in the ATD Dynamotor Cable are 8 gauge wires. I connected up everything under the desk and applied 120vac to the 80A-PS and it came up fine. I used the Throttle Switch to energize the ATD dynamotor. It takes about 1.5 seconds for the armature to come up to full speed. The Grid Current and Plate Current meters don't just "jump" to the proper current, they "ramp up" as the dynamotor comes up to speed. I had about 48 watts output with a 1:1 SWR match and the PA Plate Current was 75mA.
 

Showing the Dynamotor and the 80A-PS Location under the Desk's footwell

Setting up the ATD to run on the Dynamotor and 80A-PS - Once I had the ATD and Dynamotor running on the 80A-PS with the Collinear Array connected, I attached the 50 ft wire laying on the floor to the 51J-4 receiver in the shack. With just the 80A-PS running no RFI or noise of any kind was heard in the receiver (other than the usual ambient RF noise.) I tuned about 1mc higher than the 3.974mc that the ATD was set up on. Then, using the Throttle Switch, I put the ATD into transmit. Again, no noise was heard in the receiver except for the initial switch pulse of the dynamotor turning on. Looking at the oscilloscope, the waveform looked stable and only a slight ripple was visible at the top and bottom of the waveform. IMPORTANT NOTE: So, why don't I have any RFI Noise in the receivers when I'm using THREE switching power supplies simultaneously? The most significant noise reduction comes from having EVERYTHING grounded and shielded. The DC power supply to dynamotor input cable is fully SHIELDED. Also, a significant reduction is from having the Dynamotor to ATD power cable SHIELDED. The two ART-13 AC power supplies I built both use Lambda "switchers" for the +28vdc and, again, chassis and cabinets are grounded and ALL cables are SHIELDED. There's no RFI when using these power supplies either. All of the "switchers" that I use are Lambdas (I have some Meanwells for experimentation and test applications but for "on the air" applications, I use only Lambdas.) These Lambda 27 Amp switchers are new enough that they have the "CE" certification label that generally indicates they meet modern specifications for "low noise output." The "CE" switchers have much better filtering than the older types that were infamous RFI generators (and were in use maybe 20 or 30 years ago.) The 80A-PS has the +28vdc current availability that a PP-1104-C has but instead of weighing 100 pounds and being the size of a large stand-up laundry hamper, the 80A-PS can be picked up with one hand (weight is 15 pounds) and is about the same physical size as the ATD dynamotor. I have three PP-1104-C power supplies out in the shop. They're mounted on small furniture dollies and can be rolled around the shop, but it would be totally impractical to even try to move one of the PP-1104-Cs upstairs. They're great high-current power supplies but they aren't "portable" in any sense of the word. The 80A-PS, on the other hand, is easy to move anywhere for experimentation, troubleshooting or operation. Cost? The two recently purchased 27A Lambdas were $45 each. The older 27A Lambda was purchased last year and was $60. So, they aren't really very expensive for what you get. These are not "new" power supplies but are "pulls from working equipment, tested and working" condition. They're always available on eBay.

Operating the ATD-Dynamotor-80A-PS "On the Air" - Before going "on the air" again, I wanted to switch to the Shure 102C carbon microphone, just to be more authentic sounding. The Ch.D module has to be removed to access the microphone switch and a right-angle blade screwdriver helps due to the limited space. I powered-up the ATD and watched the wave envelope on the 'scope. Lots of symmetrical modulation and almost approaching "cut-off" or 100% negative going on voice peaks. I monitored the audio quality by listening on the HRO-7T receiver and, for a carbon mike, the Shure 102C sounds excellent. I did a quick "on the air" test with KØDWC who indicated the ATD sounded strong and "carbon-y" (a description of the typical carbon mike sound.) Also, the dynamotor noise was minimal and no other "noise" was heard on the signal. Oct 13, 2024 - Nevada Mil-Rad Net - I ran the ATD-Dynamotor combo today using the Shure 102C carbon mike and the Collinear Array. Very good conditions and the ATD was Q5 from all participants. Looking at the oscilloscope which uses a pick-up coil located inside the Johnson Matchbox, the ATD modulation looked symmetrical. All signal reports were quite complimentary about the ATD audio, even though I was using a carbon mike. Later, I was able to check the Wavelength Radio (on youtube) recording of the NV Mil-Rad Net. This recording features a panadaptor display that allows seeing what the SDR receiver picks-up. Although the modulation level looked good, it was "lop-sided" and favored the upper sideband. When looking at the spectrum, the favoring of the upper sideband wasn't so apparent and it looked like the band width from the ATD signal was about 8kc wide. None of the other Mil-Rad Net stations mentioned anything about this anomaly and it's very likely that, unless someone actually tuned their receiver from one side band to the other, they probably wouldn't actually hear the sideband difference. Since Mike's ATD also showed this same characteristic of favoring the upper side band, I assume that it's normal for the ATD. It's something that wouldn't have been heard in normal reception and would have required a panadaptor to see. Locally, with the oscilloscope monitoring the wave envelope, the modulation looks symmetrical. Other than what could be seen on the panadaptor on the recording, the actual "real time" operation on the NV Mil-Rad Net was flawless.

ATD/RBG-2 Station - CHC-49154 RBG Loudspeaker  On the far right is the ARB receiver that normally was paired with the ATD in the two-seater aircraft. The ZB-3 on top of the ARB is a Homing Adapter, a VHF converter for DFing the Aircraft Carrier. The DW-1 loop (for MW-LF) is on top of the ATD. Sharp eyes will notice the ATD Remote Channel Indicator on top of the RBG-2. I do have the original cable/connectors for the Channel Indicator but the cable needs to be repaired before using (connector on one side has broken wires inside.)

Adding a Linear Amplifier

More coming,...

The W6MIT 95 Linear Amplifier uses a Eimac Y-826 (HD 3-500Z) as the RF Amplifier

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