Radio Boulevard
Western Historic Radio Museum


NC-183 Series of Receivers

Includes NC-173, NC-183 and NC-183D
also NC-183R, NC-183MR used in AN/URR-39

History, Circuit Description, Cosmetic Issues,
Accessories, Rebuilding, Performance

by: Henry Rogers WA7YBS-Radio Boulevard

NC-183D Artwork from the Manual
shows an early version with yellow S-meter scale
although it's just artwork and might have been based on a prototype

Did National design the NC-183 and NC-183D to be much more than just a ham receiver? National promoted the NC-183 as combining "performance and versatility 'plus' for the critical user." The receiver could be used as a "top of the line" shortwave listener receiver, or, it could be used as a high fidelity reception source for various Hi-Fi applications. And then, finally, it could also be used as a "first-class" ham receiver. The less-sophisticated NC-173 was a true ham receiver geared more for the basic necessities that a radio amateur would need. The NC-173 was dependable enough to be used on the ocean-going raft, Kon-Tiki, with Thor Heyerdahl's expedition crossing the Pacific from South America to Polynesia in 1947, with the NC-173 operated at sea entirely from dry-cell batteries. The NC-183D ultimately became the most advanced receiver of the group when the NC-183 was thoroughly redesigned in 1952 with the idea of providing a receiver that could easily compete with the HRO-60 for reception capabilities but in a physical form that didn't require so many accessories and was much easier to use. So here's the rundown on National's maybe a little less-famous but still great receivers that were produced from 1947 up to 1958.

National Company, Inc.  -  NC-173, NC-183 & NC-183D

History and Circuit Description

NC-183 Receiver   SN: 241 0262   ca: 1948
Shows the light-gray, slightly silvery color used on the NC-173 and the NC-183. These initial models were fabulous receivers but their design and performance was definitely post-WWII with many of the circuits and parts used obviously from WWII design engineering.

Brief History - National introduced this style of receiver with the 1947 models NC-173 and NC-183. The post-WWII time period saw an increase in ham radio operators with many new hams being ex-servicemen that had been exposed to radio as either radio operators or as radio technicians during the war. There was also increased interest in shortwave listening due to the exposure of many ex-service men to foreign cultures during the war and also an interest in following the world events of the time by receiving broadcasts direct from overseas locations. The original advertising for the NC-173 promoted the post-WWII improvements on designs developed during WWII with 6 meter ham band tuning, a Narrowband FM option, the Noise Limiter circuit and Amplified AVC being some of the featured developments. There was no doubt that National considered the NC-173 a great medium-priced "ham receiver."

High Fidelity audio was just beginning to become popular with better recordings on newer mediums that favored wide-audio frequency range reproduction. National thought that combining SWL, Hi-Fi and Ham use into one receiver would appeal to several different types of potential buyers. "A Receiver designed to combine performance and versatility "plus" for the critical user" was National's marketing claim for the NC-183. Even the manual anticipates the variety of potential users by providing one set-up section for neophyte radio operators and another set-up section for experienced users. Unfortunately, the resulting sales favored the less-sophisticated NC-173 out selling the NC-183 by a large margin due to its much lower price and that low cost seemed to be more important to buyers than Hi-Fi audio and double preselection.

Today's vintage ham gear enthusiasts appreciate National's combination of robust Hi-Fi audio and double preselection resulting in great reception possibilities making the NC-183 and, even more so, the later NC-183D, very popular choices for vintage ham station receivers. 

The NC-173 and NC-183 - Both of these receivers were single conversion superheterodynes with the NC-183 offering double-preselection (two TRF amplification stages.) The NC-183 also featured a high fidelity audio system using push-pull 6V6 tubes for 8 watts of low-distortion, high-quality audio output power. Early NC-183 advertising stated that a Crystal Calibrator could be installed in the accessory socket but this wasn't exactly the case (unless a homebrew or kit was used.) The accessory socket was for either the National NBFM adapter (Narrowband FM) or for the National Select-O-Ject. The NC-173 and the NC-183 tube compliment consisted of mostly metal octal tubes (rectifier, regulator and audio tubes were glass octals.) Frequency coverage for all versions was from .54mc up to 30mc and additional tuning of 47mc to 55mc for 6M amateur band coverage using only the Band Spread tuning. The Band Spread tuning dial featured calibrated scales for 80M, 40M, 20M, 15M, 10M and 6M along with a 0 to 200 logging scale. The NC-173 used 13 tubes and sold for $199 in 1950. The NC-183 used 16 tubes and sold for $268 in 1950. The 17 tube NC-183D sold for an expensive $370 ($370 in 1955 was equivalent to about $4200 in 2024 dollars.)

The NC-173 and NC-183 were also available in rack mount versions that featured a black or dark gray wrinkle finish front panel. The rack mount versions used a "R" suffix in the model number. Sometimes in advertising and in manuals, a "T" suffix was used for the standard table cabinet versions (but "T" never appeared on the receiver itself.) The NC-173 was available from 1947 through 1951. The NC-183 was available from 1947 up to 1952 when it was replaced with the thoroughly updated and improved NC-183D. By the early fifties, evolution in tube types available and ham user demands for a more advanced receiver motivated National to perform a major upgrade on the NC-183 receiver with many significant circuit design changes along with many mechanical improvements that resulted in the NC-183D.

NC-173 Receiver - from KB4MTO
The front panel control layout for the NC-173 is the same as the NC-183 but notice that on the NC-173 panel the embossed area around the dials only surrounds the dials while the embossed area on the NC-183 surrounds the entire top half of the front panel.

NC-183D Receiver   SN: 430 0135   ca: 1956
Though the front panel layout was similar to its predecessor, the NC-183, inside the NC-183D was a completely different receiver, thoroughly modernized and upgraded. This photo shows the gunmetal silver-gray used on the "D" along with the black knob grips, the black dials and black S-meter scale.

The NC-183D - The new "D" version receiver really was a "different" receiver that had evolved from the old post-WWII NC-183 design into a new communication receiver that was electronically and mechanically ready for the upcoming era of crowded ham bands filled with ex-mil radio ops and many CW hams from the newly created Novice Class license. Fortunately for the vintage radio enthusiasts of today, National didn't follow the then new trend of providing "communication audio" and the new NC-183D still retained the powerhouse high fidelity audio for SWLs and ham AM operators.

Besides the use of mostly newer miniature tubes, new dials and S-meter, there were other major circuit changes such as double-conversion on the three highest frequency bands using a 1720kc Converter and a 455kc Converter and the addition of a third IF amplifier stage. The second 455kc IF amplifier used dual IF transformers that were tertiary-interconnected to provide steep sidewalls and a "flat nose" to the passband. On Bands A, B and C, there were five tuned circuits in the 1720kc to 455kc conversion process plus 12 tuned circuits in the 455kc IF. On Bands D and E, single conversion was used with just the 12 tuned 455kc IF circuits being used. This resulted in an IF passband of about 4kc at -6db, narrow selectivity for the crowded ham bands of the fifties and sixties.

There were many other subtle electronic and several obvious mechanical upgrades in the NC-183D. The 6J5 Phase Inverter used in the NC-183 was replaced with a dual triode 6SN7 with one triode acting as the Phase Inverter and the other triode used as a S-meter amplifier circuit. The mounting of the pinch wheel drive for the tuning dials was modified to be more robust working against a metal rim base plate on the dials instead of the rim-edge of an all-plastic dial (as in the 173/183.) All waxed cardboard-tube, paper-dielectric capacitors were changed to the newer molded plastic tubular paper-dielectric types or to reliable ceramic disks. Even the odd-ball speaker three pin socket was replaced with a standard three screw terminal strip (this may have happened before the NC-183D introduction.) The remote standby now had its own screw terminal strip instead of using the battery power socket.

NC-183D Top of Chassis   SN: 430 0135
The first "three in a row" cans are for the 1720kc IF. The first five of the "six in a row" cans are for the 455kc IF. The rear-most can is for the Amplified AVC. Note that the chassis tube IDs are silk-screened.

Comparison of Features - The NC-183D provided the discriminating radio owner double-preselection on all bands (two tuned RF stages of amplification) and dual-conversion on bands A, B and C (the highest frequency coverage) was employed with the IF frequencies being 1720kc and 455kc for dual-conversion and 455kc for single-conversion. As mentioned, just two stages of 455kc IF amplification were used on the proceeding NC-173 and the NC-183 receivers but an additional IF amplifier stage was added to the NC-183D bringing the total to three IF amplifier stages for that receiver. Amplified AVC that was tuned to the 455kc IF was used in all three receivers. Like the NC-183, the "D" had P-P audio output supplied by a pair of 6V6 tubes providing about 8 watts of low-distortion, high-quality audio power (11 watts maximum was available.) The audio response was flat from about 50hz up to 7Khz and at -5db at the upper and lower roll-off the audio response was an impressive 20hz up to 12Khz. National advertising for the NC-183D claimed the audio was "essentially flat up to 13kc." Definitely, the NC-183 and the NC-183D had the best audio reproduction capabilities to be found in any communications receiver available for under $500 (as National's NC-183D advertising claimed.)

NC-183 Top of Chassis    SN: 241 0262
Behind the Crystal Filter are the two 455kc IF cans. The rear-most LC (in can) is for the amplified AVC. Note the all metal-octal tubes except the 6V6GTs, the 5U4G and the OD3. Note that the chassis tube IDs are stamped into the metal.

Not my current NC-183D,...
I had this one in 2003.
I bought it with the matching NC-183TS loudspeaker at Reno Antiques for $100, a bargain even then. Unfortunately, I sold it a few weeks later out of the Western Historic Radio Museum to a visiting ham looking for a vintage receiver.

Other Details - The NC-183 Series receivers all featured a five-position Crystal Filter that allowed for a wide range of adjustability to the received bandwidth (from the normal IF passband down to about 100hz selectivity.) The Crystal Filter was also able to null heterodynes that were very common at a time when all ham voice transmissions used the AM mode. The Crystal Filter could also improve CW reception by enhancing almost any selected heterodyne tone. To further aid IF selectivity, three stages of IF amplification were used in the NC-183D. National claimed that the NC-183D IF system provided 4kc passband selectivity. This IF system was also employed in the HRO-50-1 and HRO-60 for the same reasons. Good selectivity was essential to cope with the congested ham bands of the fifties and sixties and to allow reliable communications.   

An 8 Z ohm and a 500 Z ohm audio outputs were provided from an odd-ball three-pin socket. The three-pin mini-socket was probably replaced late in the NC-173/183 production with a standard three screw terminal strip. The Tone control only reduces the upper audio frequency response leaving the lower end unchanged. National indicated that the Tone control was to improve reception for weak signals or noisy conditions and not necessarily to enhance the audio spectrum for listening pleasure.

This is an Early NC-183 showing different style cabinet rear venting and the lack of a "punch-out" hole for the Select-O-Ject accessory. Serial number is 202 0442 (built while the HRO-7 was still being produced.)

photo from eBay

NC-183R Rack Mount Receiver Version

The rack mount version used a standard 19" front panel that wasn't an integral part of the cabinet like the table models used. The flat front panel allowed for engraved nomenclature that was cut into the panel after the wrinkle finish paint was applied. In this method, the nomenclature will show the base metal, aluminum, through the paint as "bright silver nomenclature" - well, when it was new anyway. Though missing on this receiver, normally the rack mount versions had a dust cover that protected the chassis. Receiver pictured is ca: 1952

photo from eBay

The Physical - The cabinets on very early examples of the NC-183 and NC-173 were painted a light-gray color that had a slightly silver undertone. This was a semi-gloss, smooth-finish paint that was very durable but had a tendency to show any nicks and scratches quite well. The knobs used on these receivers had gray plastic knob grips. Very early examples had a punched pattern metal screen spot-welded in place on the rear panel (see photo above-right.) This was seen on a NC-183 from production run 202 from 1947. By 1948, the rear panels had horizontal-rectangular vents that were punched into the sheet metal before cabinet assembly. During the last of the NC-183 production, in 1952, the cabinets were painted gunmetal silver-gray in a smooth, semi-gloss finish, the knobs were changed to black plastic grips and some other upgrades were beginning to be incorporated into the receiver. The gunmetal silver-gray color and black knobs were carried over to the NC-183D cabinet introduced in late-1952.

Other Versions - Like its predecessors, the NC-183D was also available in a rack mount version designated the NC-183DR. The earlier NC-183 had used a dark gray, almost black wrinkle finish, panel but the NC-183DR used a gunmetal gray smooth finish front panel. There was a military version NC-183D, the NC-183MR that also had the military designation R-651/URR-39. This receiver was installed in a 30" tall table rack that included a matching rack mount speaker. The complete military-version receiver was designated as the AN/URR-39 and that consisted of the R-651/URR-39 receiver, the LS-228/U rack speaker and the MT-1529/U table rack (with shock mounts.) This version eliminated the 6M coverage and provided a LF band (50kc to 150kc) instead. The band spread wasn't calibrated for ham bands and just had a logging scale.

AN/URR-39 Receiver
photo from

Summary of Receiver Features


Produced from 1947 to 1951    Orig. Price - $199

Circuit - 1 RF Amplifier, 2 IF Amplifiers, 1 Audio Output Amplifier

Tubes used: RF-6SG7, Mix-6SA7, LO-6J5, IF-6SG7 (2), Det-6H6, AVC Amp-6AC7, NL-6H6, BFO-6SJ7,1stAF-6SJ7, Audio Output-6V6, Rect-5Y3, Reg-0D3

Audio Output Z - 8 ohms and 500 ohms from three-pin mini-socket

Tunes .54-31mc and 48-56mc

Antenna Input - Three screw terminal strip, 300Z nom.


Produced from 1947 to 1952    Orig. Price - $268

Circuit - 2 RF Amplifiers, 2 IF Amplifiers, P-P Audio Output

Tubes Used: RF-6SG7 (2), Mix-6SA7, LO-6J5, IF-6SG7 (2), Det-6H6, AVC Amp-6AC7, NL-6H6, BFO-6SJ7, 1stAF-6SJ7, Phase Inv-6J5, Push-Pull Audio Output-6V6 (2), Rect-5U4, Reg-0D3

Audio Output Z - 8 ohms and 500 ohms from three-pin mini-socket

Tunes - .54-31mc and 48-56mc

Antenna Input - Three screw terminal strip, 300Z nom.


Produced from 1952 to 1958    Orig. Price - $370

Circuit - 2 RF Amplifiers, 3 IF Amplifiers, Double-Conversion, P-P Audio Output

Tubes Used: RF-6BA6(2), 1720kc Conv-6BE6, 455kc Conv-6BE6, IF-6BA6 (3), Det-6AL5, AVC Amp-6AH6, NL-6AL5, BFO-6SJ7, 1stAF-6SJ7, Phase Inv and S-meter Amp-6SN7, Push-Pull Audio Output-6V6 (2), Rect-5U4, Reg-0B2

Audio Output Z - 8 ohms and 500 ohms from a three screw terminal strip

Tunes - .54-31mc and 48-56mc

Antenna Input - Three screw terminal strip, 300Z nom.


Receiver General Information

NC-183 dial is a plastic disk that is riveted to the metal hub

Yellow Phenolic-Acetate Dials versus the NC-183D Dials - The NC-173 and the NC-183 used acetate-based phenolic plastic dials that were pale yellow when new but nearly all of these types of dials have darken considerably to an amber-color due to the photosensitive nature of the type of plastic. These dials along with the S-meter scale were backlit resulting in one source of intense light near the dials as long as the receiver was on. Bright sunlight directly on the dials also contributed to intense darkening of the dials. There were also indications that the heat of the receiver if operated for long hours and the long-term heat/light from the lamp illumination might also have contributed to this darkening.

The NC-183D addressed this dial material problem by using copper metal-backing plates that had a plexiglass dial riveted to the front of the metal plate. The plexiglass was reverse-side silk-screened with the dial nomenclature. This gave the dial scale the appearance of "depth." These dials had to be illuminated from the perimeter edge with the lamplight going through the plexiglass which makes the silk-screened numbers very bright and visible (it requires some adjustment of the position of the lamp for optimum illumination.) The dial-lamp effect isn't quite as dramatic as the earlier backlit dials but the NC-183D dials are almost always in excellent condition (something that, unfortunately, can't be said for the NC-173 and NC-183 dials.) The S-meter scale was changed to black with translucent red numbers that glowed red when backlit. These type of S-meters also seem to age quite well (most of the time.) While the "red" on the NC-183D S-meter was "bright red" when illuminated, the "red" used on the plexiglass dials was a "brick red" color.

NC-183D dial showing the metal rim of the backing plate and the plexiglass front dial

Marion Electric/National S-Meter - The S-meter shown to the left is a NOS example that has been kept inside a box and has never been exposed to sunlight, illumination lamps or heat. It shows the correct color that the acetate-based phenolic dials were when new. The red numbers and letters show how vibrant the red was when new. I'm not aware of any reproduction dials or S-meter scales that are available at this time. According to "Radio Daze," the major supplier of reproduction dials, the only phenolic material available nowadays is dark brown. Of course, the original dials are seldom found that darkened!

Analog Dial Accuracy - As for the dial accuracy, it's fairly good considering that it's an analog dial that's electronically coupled with bandspread tuning with both dials having limited resolution. By using either received known "marker" frequencies or an external crystal calibrator reasonable dial accuracy for the ham bandspread tuning can be achieved. Many hams in the 1950s had surplus heterodyne frequency meters like the BC-221 or they had Frequency Standards that were crystal oscillators for 1000kc, 100kc and then a multi-vibrator circuit for 10kc. At the time, most manufacturers felt that the vague frequency accuracy of the receiver's tuning dial was normal considering it was an amateur receiver and extreme accuracy could always be provided externally with the operator using a frequency meter.


There's Only One Accessory Socket - Only one accessory socket was provided for either the optional NBFM adapter or for the optional National Select-O-Ject (not both, and not for a National Co. plug-in Crystal Calibrator.)

The Select-O-Ject - SOJ-2, SOJ-3 - This accessory was connected to the NC-183 or NC-183D accessory socket via a cable with plug connector on the end from the Select-O-Ject for power and routing of the signal lines. The SOJ-2 was the version that had to be used with the NC-173, NC-183. There was a "punch-out" hole in the rear cabinet panel to provide access to the accessory socket for the SOJ-2 cable (the "punch-out" wasn't on the 1947 models.) The NC-183 accessory socket had to be rewired to work with the SOJ-2 (per the National instructions but one would think it would be more prudent and easier to rewire the SOJ-2 plug to work with the NC-183 accessory socket) and the Radio/Phono switch on the receiver was used to place the SOJ-2 into operation. The NC-183D used the SOJ-3 that didn't require the accessory socket be rewired. The NC-173 also didn't require accessory socket modification to work with the SOJ-2. The Select-O-Ject was a tunable audio frequency peaking or nulling circuit usable mostly for CW but able to enhance other types of signals also. Nowadays, Select-O-Jects seem to be in the "seldom-seen" category of National accessories but, perhaps that's because the current owners just don't want to part with a versatile and usable device like the Select-O-Ject.
NBFM Adapter - NFM-83 - Starting in the late-1940s and going through most of the 1950s, Narrowband FM was thought of as a practical solution to the ever-growing problems of AM TVI and also for RFI-QRN reception problems in some locations. Since FM eliminated the amplitude variations of the signal that caused most of the TVI issues and replaced the amplitude variations with frequency variations that seemed invisible to TV watchers, NBFM seemed perfect for Voice communications for hams. The problem was that NBFM took up just about the same bandwidth, maybe a little more depending on the modulation depth, as the standard AM signal. So, although TVI and QRN issues might be gone, there was the possibility that the HF ham bands couldn't accommodate a lot of NBFM users in competition with the AM users. As a result, the FCC limited the operation of NBFM to frequencies above 27mc, relegating NBFM to 11M and 10M ham bands below 30mc. Though several manufacturers offered a NBFM function on their receivers, it never became a popular mode of transmission below 30mc. This was partially because of the transmitting frequency limitations imposed by FCC regulations that prevented wide-spread use of NBFM in the HF region of the spectrum. However later on, NBFM did become the popular voice mode on VHF, especially on the 2M band.

When the NFM-83 adapter is installed into the Accessory socket, the adapter receives its operational voltages from the receiver. Two tubes are used in the adapter, a 6SK7 IF amplifier and a 6H6 discriminator/detector. The signal input is from the IF output and AVC line via the Accessory socket and the NFM-83 output is via the Accessory socket to the receiver's audio input. The NFM-83 is essentially "in operation" whenever the receiver is turned on but the output utilizes the PHONO-RADIO switch to route the NFM-83 output to the receiver's audio system. When installed, PHONO is used for NBFM operation and RADIO is used for normal receiver operation. No modifications to the receiver were required for using the NFM-83 adapter. The NFM-83 is fairly easy to find and usually cheap since they are practically useless devices nowadays. The NFM-83 is shown in the photo to the right.

Kit-type 100kc Crystal Calibrator - I don't know of any reason that National didn't provide for using their onboard Crystal Calibrator other than economics. Certainly, had National included their typical 1000kc/100kc plug-in calibrator, that would have been the most useful of the commonly available National plug-in accessories but it would have required additional wiring for an additional accessory socket and front panel switching to operate the calibrator switching from the front panel of the receiver. That's why the HRO-50/60 receivers have two accessory sockets - to allow using a Crystal Calibrator plus either the NBFM adapter or the Select-O-Ject. Since B+ and 6.3vac are available at the NC-183 accessory socket, any 100kc crystal calibrator kit could be built to use the accessory socket of the receiver. Generally these kits will have a toggle switch on the calibrator to turn off the B+ and the output is usually just electrostatically coupled to the antenna input. The hassle is that the lid of the receiver has to be lifted to turn the calibrator on or off. Additionally, National, along with most of the other receiver manufacturers, certainly thought that any ham would have had either a surplus frequency meter or a ham frequency standard device for accurate frequency measurement of a received signal or for determining ham band edges so an "onboard" 100kc crystal calibrator wasn't considered a necessity.

Phono Input, Battery Operation - Although the Phono circuitry was used via the accessory socket wiring (pin 5) for the Select-O-Ject output or the NBFM adapter output, the Phono jack input could be used for any other sort of audio amplification as long as the input levels and the impedances matched. The SOJ-2 had to be disconnected to use the Phono input for a phonograph cartridge input. The National NBFM adapter instructions don't indicate that the adapter has to be removed from the accessory socket to use the Phono input but it probably should. The octal socket on the rear chassis apron allows access to the power supply voltages, remote standby functions and can allow a hook-up for battery operation of the receiver. Remote standby was later routed to its own three screw terminal strip on the NC-183D. As for battery operation, one famous use of a NC-173 operated entirely on dry cell batteries was the receiver used on the Kon-tiki Expedition in 1947. National advertising promoted this trans-Pacific experimental raft sailing from South America to Polynesia and its use of the NC-173 in several ads at the time. Several battery and crank-generator small transmitters were also used on the Kon-tiki.

Loudspeakers - The NC-173 and NC-183 used a 10" loudspeaker in a matching table cabinet. The NC-183 manual states that the loudspeaker was supplied with the receiver. However, the manual's inside back cover "price list" states that the receiver came with tubes, crystal filter, noise limiter and built-in power supply but then goes on to list the speaker separately as the model NC-183TS implying that it had to be purchased separately. The speaker cabinet paint matched the receiver cabinet and the style grille featured the large horizontal bar across the speaker opening with the National <NC> emblem mounted in the center circular portion of the bar. The grille cloth was a brownish woven-striped pattern. The end of the speaker cord had the necessary three-pin plug to mate with the speaker receptacle on the receiver chassis (used on the majority of NC-173 and NC-183 receivers.) The loudspeaker impedance was 8Z ohms nominal. The 10" size loudspeaker does have a pretty good bass response and sounds very nice for quality SW-BC reception.

The NC-183D used the same loudspeaker and cabinet. The cabinet paint color was changed to the gunmetal silver gray that was used on the NC-183D receiver cabinet. The three-pin plug was replaced with two spade lugs to match the NC-183D screw terminals for the audio output. This version of the loudspeaker is shown in the photo to the right. The NC-183D manual also states that the 10" loudspeaker is supplied with the receiver. The manual I have for the NC-183D doesn't have the inside back cover showing the "price list" so I don't know if it's listed in the same manner that the NC-183 loudspeaker was shown.

NC-183TS Loudspeaker for the NC-183D


Cosmetic Issues

Paint - The cosmetic department always seems to be problematic at best. The light gray-slightly silvery paint job on the NC-173 and NC-183 or the darker gunmetal gray-silver paint on the "D" was actually a very durable paint but this type of smooth semi-gloss finish paint always seems to show the "hits" that the cabinet has taken from just about anything setting on top of or next to the receiver or whenever it's moved from one place to another. Part of the problem is that the NC-183 versions are heavy receivers with "absolutely nothing" to grip when trying to carry the receiver when moving it to a new location. I'm sure a lot of the dents and scratches are due to the mover dropping the receiver or the receiver just "slipping" out of the mover's hands. The upshot is it's almost impossible to find any of these receiver-types in mint cosmetic shape. The nomenclature is stamped into the metal so a repaint might be possible although only automobile-quality paint that is "custom matched" to the original color should be used in any repaint. Almost all "off the shelf" spray-can paint will contain fillers that act as a sort of primer but using this type of paint will fill up the debossed nomenclature. The original paint was very durable but was very thinly applied and that's why it seems so prone to damage. If at all possible avoid repainting the cabinet since properly mixed paint, special equipment, correct prep and especially professional spray areas and professional painting experience are all necessary for a quality result. Often, if the receiver has decent cosmetics, a good thorough cleaning followed by a careful "touch-up" paint application is all that's necessary to get the receiver looking acceptable for a vintage ham station. It's possible that late in the production runs for the NC-183 (1952) the light gray-silver paint color was changed to the dark gunmetal gray-silver as usually found on the NC-183D. Also, the light gray knobs were changed to black knobs.

Cleaning Phenolic Dials - As mentioned, the acetate-based phenolic plastic dials used on the NC-173 and NC-183 are always much darker nowadays than they were when new. Most of the time, the section of dial that was exposed to light through the front panel dial opening will be much darker than the unexposed areas. This darkening is inside the plastic material and is impossible to correct. Sometimes a slight improvement can result with damp-cleaning the back-side of the dial. Any cleaning of the front-side of the dial should only be attempted after a test-cleaning of the part number that's located near the hub of the dial. If the part number isn't affected by damp-cleaning then the entire dial front can be cleaned by that method. I've found that plastic dials made after WWII generally have very durable ink that can be damp-cleaned, BUT TEST TO BE SURE. The NC-183 dials used very durable ink on the dials and they can be cleaned directly using a Glass Plus dampened paper towel. DON'T EVER USE WINDEX, the ammonia is a harsh cleaner, use only Glass Plus, don't scrub, don't use a lot of pressure and watch the ink for any thinning. I didn't have any ink degrading with Glass Plus when damp-cleaning the NC-183 dials yet years of dirt and tobacco staining were removed. After the cleaning, the dial will have a "flat" look but lightly polishing with a dry soft flannel cloth will impart a sheen to the plastic dial without doing any damage. This dial cleaning won't change the darkening that has happened because of sunlight. That discoloration is deep inside the plastic material. What the cleaning does is remove other types of dirt on the surface of the dials and that will generally brighten the dial somewhat and increase the contrast between the dial color and the nomenclature. Cigarette smoke contamination on the phelonic-acetate dials is the most common "dirt" that can usually be easily removed on post-WWII dials, but be sure to test the silk-screened ink on a non-visible area first. 

NC-183D Band Indicators - Another cosmetic problem involves the plexiglass dial covers and the white paint fill on the band identification markers used on just the NC-183D. The engraving is very, very,...well,...extremely shallow and the white paint can be easily worn off with just the normal cleaning over the years. The shallow nature of the engraving prevents re-doing the white fill paint in a normal manner. The shallow nature has any attempt to remove excess fill-paint impossible because the "wiping action" tends to "pull" the fill-paint out of the engraving. Worn original white fill-paint seems to be a very common cosmetic problem that's almost impossible to restore - at least, I've never found a successful method to accomplish it. I've even tried a rubber squeegee without success. I haven't tried Lacquer Stiks but the white ones tend to be "very bright white." National must have had some process to accomplish the white fill of the nomenclature on these NC-183D band indicators but I haven't discovered it yet. NOTE: I've ordered some white Lacquer Stiks to experiment on the NC-183D "parts set" band indicators that are in very good shape except there isn't any white fill left in any of the engraving. I'll update the results here.

All of these special and difficult to solve cosmetic issues seem to justify the high prices that a "near mint" NC-173, NC-183 or especially the NC-183D can garner today.

General Information on Rebuilds

Electronic Rebuilds - NC-183D - Many as-found condition NC-183D receivers will have a variety of operational problems nowadays generally due to poor storage, hamster rework in the form of "junk box components" used for repairs that are "hook-spliced" into the circuit. Sometimes unnecessary and destructive modifications are incorporated into the circuit. In addition to those problems, some original leaky paper-dielectric capacitors can potentially cause heat-related failure of the power transformer if the receiver is operated for long-hours without a proper rebuild. A full rebuild and complete alignment is normally required to obtain the "top performance" that the NC-183D is capable of providing. If you're planning a NC-183D rebuild, there are 16 molded-plastic-tubular, paper-dielectric capacitors to replace but, luckily, a large number (all but five) of the .01uf capacitors are ceramic disks that won't require replacement. There are 5 electrolytic capacitors that will probably need replacement. Reform and test at full operating DC voltage if you plan on using the original electrolytics. All components are easy to access. Check the carbon resistors for being out-of-tolerance since any leaky bypass capacitors can easily over-heat associated load resistors. Many of the 470K resistors are in parallel with other components in the circuit and will not measure their actual value "in the circuit" and will need one lead "lifted" for accurate measurement (if you feel it's necessary - like if you're having trouble with the circuit.) On replacement parts, use only new capacitors. Polyfilm "Yellow Jackets" will work fine but CDE 715P Orange Drops also work fine and will make the rebuild look more professional. Replacement resistors should be NOS JAN CC types (10% tolerance or better) if possible, and their value must be verified with an accurate resistance measuring device (some brands of carbon resistors will drift in value even if they have never been used. Allen-Bradley JAN types are the best for holding their value.) Replace any tubes that don't exceed minimum acceptable transconductance by a significant percentage (NOS tubes are best.) Finish with a complete IF and RF tracking alignment and your NC-183D should become an easy-to-use station receiver that provides excellent sensitivity, the necessary selectivity if you use the Crystal Filter and very high-quality audio reproduction if you use the original National 10" table loudspeaker or perhaps even a better speaker set-up.

NC-173 and NC-183 - These earlier receivers have wax-covered cardboard shell, paper-dielectric capacitors installed (and there are a lot of 'em - 26 paper-wax types to be exact, four rectangular bakelite molded paper caps - 30 paper dielectric capacitors total for the NC-183.) The four rectangular-shaped, brown-molded plastic capacitors look like over-size micas but are actually .05uf 600wvdc paper-dielectric capacitors and these should also be replaced (these are WWII surplus components that many manufacturers used post-WWII.) Check electrolytic capacitors for value and leakage current. The filter electrolytics will probably need replacing but the filter capacitor is a high-quality unit with an excellent seal and it might function after reforming but be sure to reform and test at full working DC voltage. Most of the NC-183 series receivers I've worked on had the original filter capacitor unit and it seemed to function fine (but I still don't know if I'd trust it for long hours of operation.) Also, many times the cathode bypass electrolytics are still good (low operating voltage and small size provided excellent sealing preventing most of them from drying-out. Testing and reforming will be required - but replacement is probably a better option for top performance of the hi-fi audio section.) Resistors should be checked for values versus tolerance. Basically, it's the same procedure as with the "D" model but with 14 more paper-dielectric capacitors to replace.

Expected Performance

Performance in General - The original advertising (and even the manual) for the NC-183 indicate that National wasn't building the receiver specifically for hams. The manual has one section for neophyte radio operators and another section for experienced users. The post-WWII time period did have a lot of interest in shortwave listening due to world events going on at the time. In addition to that, High Fidelity was just beginning to become popular. National thought that combining SWL, Hi-Fi and Ham use into one receiver would appeal to many potential buyers. Hallicrafters had the same idea with their post-WWII SX-42 receiver in trying to appeal to more than just the ham market by providing FM reception from 27mc up to 108mc with hi-fi audio capabilities. Unfortunately, the upshot was that the less-sophisticated NC-173 out-sold the NC-183 by a large margin due to its much lower selling price and that low cost seemed to be more important to buyers than Hi-Fi audio and double preselection (Hallicrafters had the same experience with the SX-42 being outsold by their less expensive receivers.) But, today's vintage ham gear enthusiasts appreciate National's combination of robust audio with great reception possibilities making the NC-183 and, even more so, the NC-183D very popular choices for vintage ham station receivers. Additionally, these were very well-built receivers that used top-quality components. The chassis and many of the steel parts are nickel-plated. Other chassis components have a matte-aluminum finish. The NC-183D chassis is often found in beautiful condition, though it does depend a lot on how well-cared-for the receiver was during its active period and then where the receiver was stored afterward.

NC-183D - The vintage AM ham users favor the NC-183D primarily because of its double-conversion, its tertiary IF system that also provided an extra stage of IF amplification and its superb high fidelity audio reproduction. The receiver accessories could include the NC-183TS, a 10" PM loudspeaker in a matching housing. The original 10" National speaker actually sounds very good, but, these large 10" versions are becoming more and more difficult to find along with its ever-increasing expense to purchase them when they are in good condition. However, if a larger speaker system is available, the NC-183D can produce really fabulous audio on AM signals. Lots of bass is available and the IF bandwidth is sufficient for fairly wideband audio reproduction (I use a 15" Jensen coaxial speaker housed in a Jensen KM bass-reflex box - described further down.) The audio bandwidth specs are a surprise for a communications receiver and feature a -5db 20hz low end, flat from 50hz to 7khz and an expected drop off beyond that to -5db down at 12Khz. It's too bad that AM-BC programming is so dismal (around here it's nothing but sports-talk, poli-talk and the aurally torturous country-western stations on AM ) and quality SW-BC is also a rarity these days. Well, there's always low power DIY BC-ing. Or, for better signal quality, you can use a lab-type RF signal generator and feed your CD-player (showing my age,...sorry,...your MP3 device) output into the EXT. MOD input, adjusting the sig-gen modulation gain level for a quality waveform. Then connect the RF sig-gen to the NC-183D antenna input and decide on a frequency to use. It's like having whatever programming you want delivered via cable to the receiver. Of course, audio quality is highly dependent on the type of external equipment used for this "hook-up."

The NC-183D is also sensitive enough and provides adequate selectivity to deal with most actual ham band reception issues. I've used the NC-183D as a station receiver on 75M and it's easily able to cope with all of the QRM and QSB issues along with having a good ability to provide Q5 copy of very weak signals in the AM mode. It's also convenient that remote standby is very easy to set up and use. When examining the specifications one will notice that the NC-183D has almost all of the features of the HRO-60 but minus the headache of dealing with plug-in coil sets that have to be manually extracted from the receiver to change bands or to be switched between general coverage and ham band spread coverage; or the expense of purchasing additional coil sets if coverage other than 1.5mc to 30mc was desired; or the problem of how to store unused coil sets or dealing with a PW-D micrometer dial that was pretty much useless by the HRO-60 production (the PW-D had to be installed, otherwise it wouldn't have been a HRO.) Maybe you can't use the plug-in National Crystal Calibrator on the NC-183D but there are other methods for externally determining received frequency. If you want the performance of the HRO-60 but with less accessories and in a more convenient-to-use form with features like simultaneous band spread and general coverage operation, tuning range changes via a front panel band switch or high fidelity audio, the NC-183D is that receiver. Likewise, the earlier NC-183 was intended to be competitive with the first HRO-50 version. 

NC-183 - The earlier NC-183 is obviously lacking some of the more sophisticated design features of the NC-183D, but the NC-183 was from where the "D" evolved. Even though it's the early version, the NC-183 was considered a "hot receiver" when it was introduced in 1947, least according to National advertising. Nowadays, when the NC-183 is rebuilt and aligned, it will perform somewhat like the "D" although having only two stages of IF amplification using standard IF transformers will result in a broader IF passband that will tend to favor the hi-fi audio capabilities of the receiver when listening to quality AM broadcasts (if they exist.) The Crystal Filter can narrow the passband as needed and will probably only be needed occasionally. Crystal Filters can easily be used for AM reception and are excellent for reducing adjacent frequency SSB QRM. The single-conversion design really only adversely affects performance on the highest frequencies. Up to about 15 meters, the NC-183 does a great job. Above 25mc, the NC-183 begins to show its WWII design roots as the sensitivity falls off noticeably. Mechanically, the tuning on the NC-183 can have problems since the plastic dials are rim-driven with a pinch-wheel system. If the plastic dials are damaged along the rim, they will never work correctly (and these dials can be damaged easily by careless removal of the chassis from the cabinet.) The odd-ball three pin loudspeaker socket is a hassle to find a plug that fits but using just the correct size metal pins to fit the one large socket receptacle (chassis ground) and to fit a smaller pin for either 8Z or 500Z outputs will work fine and eliminates trying to find the almost unique plug. Of course, the NC-183 is the older version but the NC-183D seems to "age" quite well and is generally found in much better condition. The NC-183 will almost always need major rework and rebuilding to get it performing up to its original capability. I've also used the NC-183 (rebuilt) as a station receiver on 75 meters and have found it able to cope with all of the normal QRM issues. 75 meters isn't much of a challenge for almost any receiver and selectivity becomes the most important facet of performance when operating on this band.

NC-173 - The NC-173 might have problems with images starting around 20 meters. To a certain extent, actually hearing images will be related to the incoming signal strength so a very large or a high gain antenna might actually allow more images to be heard than a simple antenna system would. One does have to consider (as maybe the original purchasers did) that most ham operations will be on 80 or 40 meters where images won't be a problem and the receiver's selectivity becomes the important performance issue. If frequencies higher than 14mc were of interest, it was always possible to add an external preselector to improve image rejection. The audio output on the NC-173, being that it was intended more as a "ham receiver," uses a single 6V6 audio output tube although the audio specifications are still almost hi-fi.

On the NC-173 receiver,...I've owned one NC-173 receiver and have inspected several. The one I owned had belonged to Reno ham Al Chin, who maintained the police radios for the City of Reno. Al had installed one WE 717A tube in the IF. The 717A was a "plug-in" substitute for the 6SG7 that provided better gain at lower noise. This NC-173 performed quite well and was in fair cosmetic condition. I sold it to a guy in Australia (this was years ago.) Another NC-173 that I almost owned was in very nearly mint condition and had belonged to W7NOM (from Ontario, Oregon.) A collector friend of mine had acquired some of W7NOM's ham gear at an auction in Fallon, Nevada. His plan was obtaining the gear as a donation for my radio museum in Virginia City. Included was W7NOM's NC-173 and his beautifully-built homebrew transmitter. Out of consideration for the donation, I convinced my collector friend to keep the NC-173 and I'd take the rest of the gear as the donation. I still have the W7NOM homebrew transmitter,...this transmitter also has a beautifully-built external VFO that uses a National vernier dial for tuning. I did see another beautiful condition (close to perfect) NC-173 at a ham swap meet in Fallon, Nevada several years later. The excellent cosmetic condition was impressive and, additionally, it was in completely original condition under the chassis (I actually removed the bottom cover to look!) It was bargained priced at $100 and was purchased by a fellow Nevada ham friend of mine who acquired it for an out-of-state ham friend of his. Since the NC-173 only has one RF stage of amplification and only a single 6V6 audio output, it doesn't have the hamgear-collector appeal that the NC-183 receiver or especially the NC-183D receiver have. But, sometimes near-perfect cosmetics can compensate for potential performance deficiencies for hamgear collectors, especially since finding any of these receivers in great cosmetic condition is such a rare occurrence.


Restoration Write-Ups

Rebuilding NC-183D  SN: 430 1035

Apr 2022 - Another NC-183D - I must have a soft-spot for the NC-183D. I've owned several of them over the years but I always seemed to sell them off after a short time. Even the one shown in the photograph above in the "History and Circuit" section is actually one that I owned 20+ years ago. I sold the last one I had in 2019. I had acquired it the year before from Ham & Hi Fi in Sparks, NV as a "tech special" (cheap because it didn't work and couldn't be sold to inexperienced collectors on eBay.) The exterior was in excellent cosmetic condition. Inside, the chassis was in beautiful condition except the original power transformer had been removed and a standard replacement type power transformer installed. I had a NC-183D "parts set" that provided an original power transformer. Then I recapped the receiver (the paper dielectrics only) and that was followed with some tube replacements and a full IF/RF alignment. I sold it to a local ham that was looking for a NC-183D off of eBay. I sold him this one for about half of what an eBay purchase would have been. In 2022, I found out the ham I'd sold it to had put the NC-183D "in storage" and hadn't even been using it because of some "microphonic tube" problems. I offered him a trade of some ART-13 transmitter repair work he needed for the return of the NC-183D receiver.

I repaired the ART-13 (burned-out field winding on the Autotune motor - required a new motor installation) and got the NC-183D back. Its serial number is 430 0135 indicating it's a fairly late production receiver probably from one of the last NC-183D production runs. Production of the NC-183D ran until 1958 while the HRO-60 was produced up into the early-1960s (the latest production run HRO-60 serial number reported is on run 505 but the HRO-60 production starts at run 357, then 366, 393, 425 and the last two runs are 459 and 505.) The trade also included that same pretty nice NC-183D "parts set" that's been "kicking around" for quite a while (I had to "take it back" as part of the trade deal!) The "parts set" was an unfortunate victim of hamster modifications that seemed to zero-in on the dual-IF (tertiary style) part of the circuit. Rampant physical damage pretty much relegated this NC-183D to "parts set" status. "Parts sets" are really a necessity for restorations and rebuilds. Except for storing them, they are really convenient to have. The serial number of the parts set NC-183D is 357 0668 (run 357 was also used for the first HRO-60 receivers.)  

But,...back to the NC-183D problem,...the "microphonics" turned out to actually be "motorboating" that was caused by a leaky 6BA6 tube used as the 2nd IF amplifier. I had been all through this receiver just a couple of years before and had replaced all of the paper dielectric capacitors, so I was pretty sure the problem would have to be "tube related." I replaced the bad tube and the receiver was "back to normal." Now, I'm using this NC-183D to drive a 1950s vintage 15" Jensen coaxial speaker housed in a 1940s vintage Jensen KM bass reflex cabinet. Wow! Great sound,...even some of the SSB signals seem to have extended bass in their audio. The NC-183D is one of the few post-WWII ham receivers that can provide enough audio power to drive the Jensen KM bass reflex box effectively. Though P-P audio was common on many "high-end" ham receivers pre-WWII, after the war, most ham gear came with "military-grade" audio that was promoted as "communication audio." The favored audio response for "communication audio" is 300hz to 3000hz - great for a carbon mike used on the battlefield - not so great for anything else.

As for AM-BC reception,...absolutely nothing of interest to listen to over the air around here. Shortwave BC has a few interesting stations and in the mornings mainland China SW-BC stations "pound in" here. The Chinese stations have excellent audio with lots and lots of modulation and very wide audio bandwidth. Sometimes interesting idiomatic music,...for a large variety of Chinese percussion instruments accompanied by mirliton soloists (a mirliton is a membranophone with finger-holes like a recorder-type flute but it sounds like a kazoo) try Firedrake, the PRC jamming station located on Hanon Island. If you can manage to listen to Firedrake long enough, you'll notice that the music is on an approximately one-hour long "loop" that just keeps repeating the same program material, over and over and over,...well, it is a jamming station,'re not really supposed to enjoy listening to it.

I know,...this write-up is kinda brief. Maybe I'll be adding more to it with some detailed photos of the chassis top and bottom. Unfortunately, when I recapped this NC-183D I used "yellow jacket" polyfilms and I don't remember exactly how I installed them,...that is, was I in a hurry?,...or did I do a professional job? If I were doing that recap job these days, I'd use the CDE 715P Orange Drops, rebuild the solder joints and absolutely not use "hook splices" for the installation. Hmmm,...I might be able to expand this write-up some more and it would only involve replacing 16 capacitors,...I'm sure I could find some other things that need to be done to this great example of the NC-183D, trying to figure out some restoration method for the band indicators,...more to come? It's a possibility, fact, I've already ordered the CDE 715P caps,...

photo above: My current NC-183D SN: 430 0135 is setting on top of the Jensen KM Bass Reflex Box with a Jensen 15" coaxial speaker inside. The NC-183D is one of the few communication-type receivers that can really drive this speaker box. 8 watts of audio is available and up to 11 watts peak audio. The shop antenna used is a 130' CF Inv-Vee fed with 44' of open feed line and using a Nye-Viking MB-V antenna coupler.


Restoring the 1948 NC-183  SN: 241 0262

If you were disappointed at the brevity of the proceeding NC-183D restoration write-up, I'll try to make up for it with the following restoration write-up about the NC-183. It's written in my typical OCD-style with protracted descriptions, a copious amount of photographs and maybe a few helpful hints. This NC-183 looked like it had excellent cosmetics on the outside but hidden terrors lurked inside were many repairs had been accomplished with "junk box parts" installed in the most indifferent amateur manner possible. On top of the lack of workmanship quality there was the evidence of ownership by a five packs-a-day, chain-smoking operator that must have blown his cigarette smoke into the receiver hour after hour. And, if smoke-contamination wasn't enough, literally everything mechanical that moved had been slathered with grease,...even the pinch-wheel dial drives and even the band switch. Well, this receiver's restoration should provide some interesting commentary and observations.

NC-183 Receiver  SN: 241 0262   ca: 1948
This NC-183 is on production run 241 which is before any of the HRO-50 production runs that start at run 280. The last HRO-7 receivers were produced on run 232 and that indicates that this NC-183 was produced shortly after the last of the HRO-7 receivers, probably sometime in 1948. The earliest run number seen on a NC-183 was 202, produced in 1947. The dials on the receiver shown have the typical darkening of the phenolic-acetate dials. This photo was taken before any cleaning or restoration was performed and shows the great condition exterior.

NC-183 Initial Inspection - Jan 11, 2024 - The receiver cabinet was taken apart by removing the bottom cover then removing the rear panel and lid assembly. The knobs had to be dismounted, then the dress nuts on the switches and the phone jack. Before removing the chassis from the cabinet the two dial guides above each of the dials have to be removed. The four felt-cupped feet had to be dismounted and then the cabinet can slide forward to have the chassis fully exposed. I pulled all of the tubes and placed them in a box with the knobs and hardware.

The next step was to test the "iron." The power transformer supposedly was tested by the seller and it did test good. The filter choke however was open. This choke is exactly the same part number as the filter choke used in the HRO-60 receivers, SA-6294, of which I had a spare. Also, the parts set NC-183D had the same part number choke still in place. So, that was lucky. The audio output transformer tested good. All of the IF transformers tested good.

The visual inspection revealed that a few capacitors had been replaced over the years (two with molded plastic paper-dielectric types and one with an orange drop.) Also, two ceramic disks were added to the 1st RF amplifier and the Mixer tubes that connect the suppressor grid to chassis but the suppressor grid was already wired directly to chassis so I don't know what the intention of these capacitors were (but replacements will not be installed.) Also, three of the four square brown plastic molded capacitors were split-open (see photo below.) It doesn't look like these capacitors "blew" or "swelled." It looks like the plastic housing just split apart for some reason.

Tuning condenser front mount nuts were very loose. Had to tighten from underneath after removing the two dial pinch-wheel drive mechanisms (these nuts actually have to be adjusted when setting up the pinch-wheel drive for each dial.)

Other Mechanical Problems - The tuning dial was completely immoveable but the band spread dial worked fine. Both of the pinch-wheel drives were not engaged to the rim of either dial. The Noise Limiter control is frozen in place. The loudspeaker output connector is a special three pin mini-socket type.

Probably from the indifferent packing, the rear panel is bent in two places. This is causing the lid to not set square in the recessed opening of the cabinet. Also the front lower lip of the cabinet has a slight bend. Closer examination actually revealed many more bends to the metal, especially in the lower front panel area.

Main Dial Drive - The drive gear shaft was frozen in the bearing. I found that dirt and grease had hardened and heat broke it loose. I still had to disassemble the entire drive because of rough, grating feel to the tuning. I pushed the shaft out of the bearing and found the set screws had galled the shaft. I filed the galled area to allow easy reassembly. I had to clean and lube the washer-spacers and the shaft. When reassembled everything worked smoothly. The dial rim was not engaged into the pinch-wheel so by loosening the pinch-wheel mounting I could get the dial rim into the pinch-wheel. Although both of these dial drive mechanisms for both dials need to be thoroughly cleaned, it is working smoothly now with some slipping due to the dirt-contamination. Later, I took a closer look at the Band Spread dial mechanism. I could see that the drive gear had quite a lot of wear that was probably due to excessive anti-backlash pressure. I had to disassemble the Band Spread drive to clean and relube. After that the tuning was still rough-feeling caused by the excessive wear to the drive gear teeth. I harvested an excellent condition drive gear from the NC-183D "parts set" (the gears are the same part number and exactly alike) and installed it into the Band Spread tuning. I adjusted the anti-backlash split-gear for just enough pre-set for proper operation and then "snugged up" everything. Now the Band Spread and the Main Tuning drives are both very light feeling and the pinch-wheels shouldn't have any problem driving the Tuning and Band Spread condensers.

Removed and Cleaned Dials - I used Glass Plus to remove the nicotine staining then polished with a soft flannel cloth. Wrapped with paper towels for protection until I'm ready to reinstall. Finished dials are shown to the right. The remaining discoloration is inside the plastic and can't be removed.

S-Meter - Dismounted the S-meter for later cleaning. Stored in the parts box.

NC-183 Dials after damp-cleaning. This is about as good as these acetate-phenolic dials can be cleaned. The discoloration is deep in the plastic and can't be removed. Though the red looks totally faded, when back-lit, the red becomes very visible. The cleaning also increased the contrast of the black nomenclature to the amber background.

Photo above shows the chassis before any cleaning. Grease and dirt combined with tobacco smoke,...yuk!

Noise Limiter - Frozen Shaft - Heat was used in combination with WD-40 to work the control shaft loose. It took several applications but finally it was working normally. I noticed that someone had turned the NL control while the shaft was frozen and actually rotated the potentiometer. I had to dismount the RF Gain pot and the NL pot to get everything oriented correctly. Ultimately this pot tested as defective and had to be replaced with an original NL pot that was harvested from the NC-183D parts set. Luckily, the NL circuit hadn't changed in the evolution of the receiver model so the pots were identical.

Replaced the Filter Choke - I removed the open choke and installed the spare unit that had come out of a HRO-60, it was the same part number. Since the original was open, it's possible that its open condition actually "saved" the power transformer from subsequent damage from those "let's plug it in and see if it works" types that expect miracles from three-quarters of a century old components.

Cleaning - The entire chassis was filthy. Most of the greasy dirt came off fairly easily using WD-40 followed by Glass Plus. I found that just Glass Plus worked somewhat better on the smoke contamination. The chassis is nickel-plated (or something like nickel) so it cleans up nicely. I used a brass bristle brush with lots of Glass Plus. Since the brass is softer than the nickel it only removes dirt. The aluminum pieces can only be cleaned using an acid brush or similar soft-bristle brush otherwise the aluminum will be scratched. The stamped part numbers on the individual components used a very durable ink that is resistant to Glass Plus which is nice. Some severe tobacco staining required denatured alcohol, probably to break-up the tar component of the cigarette smoke deposits. That was then again followed by Glass Plus cleaning.

Photo above shows the cleaned chassis but without dials mounted or tubes installed. That's the HRO-60 filter choke installed, it's the exact same part number as the original choke.

Tuning Condenser Cleaning - This area had a lot of grease along with tar and nicotine contamination. I removed a lot of it using Glass Plus. For the most stubborn contamination I had to switch to denatured alcohol. I had already removed the plastic dials but, if denatured alcohol is going to be used, you also have to avoid any contact with the ink lettering or ink-stamped part numbers. The ink is tolerant of Glass Plus but it probably wouldn't survive too much denatured alcohol. I used an acid brush to flush the tuning and bandspread condensers, the ceramic insulators and the area with denatured alcohol followed by Glass Plus. Really disgusting how the "smoker contamination" permeates to all areas of the top of the chassis. Underneath the chassis isn't too bad, minor contamination where the dials come through the chassis,...probably because it's at the front of the receiver, it's a large opening and it's nearest the smoker-operator. So, the under side just required a little "spot cleaning." In addition to the smoker's contamination, sometime in the past someone "greased" every moving part, including the band switch and the rotor contacts on the tuning condensers. Grease is actually slathered everywhere and that makes cleaning even more difficult.

Audio Gain Pot - This was a "splined split-shaft" replacement that didn't allow mounting the knob correctly. Easy to replace,...or so I thought. Examination of the NC-183D "parts set" revealed the change in that receiver when compared to this earlier NC-183. The AF Gain pot incorporated the AC power switch on the NC-183D, so I had to go to the "used pot box" for a proper type of potentiometer. I found a couple of 500K Audio taper pots that looked very much like the original style (these were Clarostat types.) I selected the one that tested the best and installed it. I'm not sure what the original pot's taper was since it's not mentioned in the parts list. The Audio taper will allow a slow increase in audio gain to about 60% advanced, then a rapid increase in gain for the remaining 40%. It makes the actual "listening-level of volume" easier to adjust. Photo right shows the new Audio gain pot installed.

The .05uf 600vdc capacitor is split-open. Note the ceramic disk is connected from suppressor-grid to ground - not an original component.

Replacing Capacitors - There are thirty paper dielectric capacitors that will need to be replaced. There aren't any weird values, just the typical .1uf, .01uf, .05uf and one .25uf. The .05uf capacitors, of which there are four, are the rectangular brown molded plastic body types. The photo to the left shows one of the four .05uf 600vdc bakelite capacitors that split apart (3 or the 4 are split-open.) The other capacitors are the typical Aerovox brand tubular wax-covered types. The mica capacitors are usually only replaced if found defective. There are five electrolytic capacitors. The filter capacitor is a dual multi-section both 10uf at 475vdc. There are two cathode bypass electrolytic capacitor and one addition power supply (bias line) electrolytic. There's a .1uf capacitor across the filter choke to somewhat tune the filtering (parallel LC at resonance is a high Z, probably tuned for 120hz.)

I'm not going to bother with "restuffing" the original capacitor waxed-cardboard shells.  I'm going to use orange drops for all of the replacement capacitors. I've never had any trouble with the polyfilm "yellow jackets" but their bright yellow color and small size make any recap job look like the cheapest parts available were used. Orange drops aren't too much better in the "looks department" but the Type 715P uses polypropylene as the dielectric material and they are "more accepted" by rebuilding technicians for a recap job because of their reputation of quality. Photo right shows under the chassis before any capacitor replacement. The three "as found" replacements are easily spotted in the photo (the blue cap next to the replacement Orange Drop is the wrong value. The Orange Drop is also the wrong value,...hmmmm,...junk box parts.)

Under the chassis before any rework

Jan 16, 2024 - Need Capacitors - Despite a long search, I couldn't come up with enough orange drop capacitors on hand here to do the recap job completely. Although I found almost enough capacitors, they were a mixed assortment of new and used vintage Sprague, not-so-new SBE, new CDE and other types of orange drops that "sort of matched" but really didn't. I'd rather install all new CDE Type 715P with polypropylene dielectric for all of the capacitors than to use a mix of different types and vintages. The order will be placed tomorrow (it was, Jan 17.) So, since I'll have a few days, I'll take a look at all of the resistors under the chassis. I'll replace any that are over 25% out of tolerance. I'll also have to do some work on the cabinet. I noticed that the lower front panel is "dished in" probably from the poor packing job and resulting shipping issues (the seller used FedEX as the packer - big mistake!) With the knobs installed, this bend isn't too noticeable but it's there,...along with a center bottom vertical bend where the center of the front panel was "pushed in." These are minor bends that aren't very noticeable unless you know they're there. Then they're obvious. Also, when the cabinet is assembled the misalignment is then very noticeable and is due to the bent metal. I'm pretty sure careful "bodywork" can straighten out the cabinet without damaging the paint. The back panel and hinged top also need a little "bodywork" since a right top back corner bend is causing the lid to not set straight in the lid-well when the cabinet is fully assembled. I'll also fully clean the cabinet which actually looks really good until it's examined closely and then the smoker's residue is apparent. Straight and clean should be an improvement that should be noticeable. Jan 18, 2024 - Checked resistor values - All checked within 25% except some of the 470K which is normal for the NC-183. I checked the NL pot that had been twisted with the frozen shaft. It doesn't measure as expected, in fact, it appears to be open which isn't too surprising after its other problems. I checked the NC-183D schematic and its NL pot is identical to the one used in the NC-183 (100K with DPST switch,) so I'll harvest that one out of the "D parts set"  The other potentiometers tested okay.

Touch-up Paint - I bought some Testor's model enamel paint (small glass jars) to mix up an exact "touch-up" paint for the very light gray with a touch of silver. I had to do the same thing for RACAL's "Admiralty Gray" which is actually a very light green color. The mix for the NC-183 & NC-173 light gray with a touch of silver is Machine Gray (5 parts) + Silver (4 parts) + White (3 parts) + Yellow (1 part) + Brown (a dab.) Use a mix of gloss and flat paints to end up with semi-gloss (2 gloss to 3 flat is about right.) The mix-hue when wet has to be just slightly lighter than the cabinet paint because most paints dry slightly darker. The mix will get you close but each cabinet has aged differently so you will have to vary the mix slightly to match. Also, match using sunny daylight from a window or two for ample natural light that won't skew the colors. Don't have any lamps on,...lamps tend to skew the color match. I didn't apply the touch-up paint until after the receiver was completely reassembled. The last photo in this restoration write-up section shows the NC-183 after the rebuild was completed and the touch-up paint applied.

Jan 19, 2024 - Noise Limiter Control Replacement - Harvested the Noise Limiter control and switch out of the "parts set" NC-183D. The NL control was almost identical to the old pot and switch that was in the NC-183 with the exception that the switch that had a slightly different orientation but the function was the same. I cleaned all of the terminals with solder wick and then tested the pot and switch to make sure it was a functional unit. To install the NL switch is fairly difficult because of its location in the front corner of the chassis right next to the bottom with very little clearance and with the wiring harness directly underneath the pot. I had the NC-183 chassis up on one end to allow easy viewing of the NL pot location. The RF gain control has to be dismounted and pushed to the side out of the way. There's a 270K CC resistor that connects to the center terminal on the NL pot that has to be unsoldered along with the .1uf capacitor connected to the NL switch to actually be able to move the NL pot out to be able to unsolder the two wires that connect to the NL pot and then the one wire that connects to the NL switch. Once disconnected the old NL pot/switch was removed. The wire leads were reconditioned. I had to rearrange the wiring harness to have the new NL control actually fit without smashing down on the harness when mounted. Once the NL pot fit in place correctly, the wires and components were connected and soldered (except for the capacitor which will be replaced during the "recap" part of the rebuild.) The RF gain pot was remounted. Installing the NL pot took about an hour because of the "tight quarters area" and trying different arrangements of the harness until one was found that worked. Jan 20, 2024 - Cabinet Work - Since the capacitors still haven't arrived, I moved on to the cabinet. The index fiducials are removable since they are mounted with two screws. There are also two dial guides that are held in place with two screws each. The plastic window with the band indicators is mounted with four screws and nuts along with a rectangular metal spacer on each side. Removal of this hardware allows taking out the plastic window that is actually one long piece of thin and flexible plastic. As expected, the plastic window was extremely dirty and had lots of smoker's residue. I had to use Glass Plus to clean both sides of the plastic window three times to remove all of the contamination. The cabinet was cleaned inside and out with Glass Plus. I had to use a soft-bristle brush to scrub the areas that had a lot of smoker's residue. After two cleanings, the cabinet looks pretty good. It will need to be "touched up" but not extensively. The most serious problem is the front panel bend. Straightening the cabinet to be square without damaging the paint (any more than it already is damaged) will require using thin padding (I use heavy stock paper) against the paint to protect it when the bodywork is performed. I taped the paper padding to the front of the receiver using blue masking tape. I used a piece of hardwood as the "anvil" and another piece of hardwood for the "dolly." A few times I had to use the hammer directly on the inside metal of the cabinet to get it to bend correctly. It took about 15 minutes to get the cabinet straight. I also had to work on the rear panel but these bends were easily straightened using other techniques. I put the cabinet together to see how everything fit now that it was straight and no problems were encountered when threading in the screws. The cabinet does set straight and looks "square" now.
Jan 21, 2024 - Miscellaneous Work - Disassembled both to the pinch-wheel drive assemblies to remove all of the grease, dirt and other contaminates that were all over and inside the assemblies. Cleaned everything with denatured alcohol and then lightly lubed the bearings with red wheel bearing grease. The actual pinch-wheels have to be completely clean to grip the plastic dial perimeters. The dial perimeters also have to be thoroughly clean. Reassembled the drives and they are ready to install after the capacitor rebuild.

I also reinstalled the plastic dial cover. The dial index fiducials were cleaned and needed just a little straightening before installation. The dial guides (these keep the dials from rubbing against the dial index fiducials) were cleaned, adjusted and reinstalled but these have to be removed before the chassis is reinstalled into the cabinet. The pinch-wheel drives, the dial index fiducials and the dial guides all have to be adjusted after the chassis is installed into the cabinet.

Jan 22, 2024 - More Cabinet Cleaning - In some types of light, I could see there was still that yellowish smoker's residue on the cabinet. I wouldn't recommend the following treatment unless it's tried on someplace out of sight first. Denatured alcohol seemed to be the best for removing the most difficult of the smoker's residue. I tried the inside rear panel first and the smoker's residue came off and, most importantly, the paint was not affected at all. I continued on, cleaning all sides of the cabinet using denatured alcohol and clean paper towels so I could see what was coming off and it was always the yellowish brown color of tobacco smoke. I never saw any indications that the paint was being affected but I'd say that 99% of the smoker's residue is now removed from the cabinet.

Jan 23, 2024 - Degreasing - I used DeOxit to thoroughly clean the band switch. To make sure that all of the grease was removed from the contacts, I used a small paint brush to apply the DeOxit just where it was needed. There were places that had grease applied that needed more detailed cleaning, like two or three brush applications, to remove the white-colored grease that had been used (unbelievable!) The Tuning and Band Spread condensers were also "greased" at all of the rotor contacts and required additional cleaning. I had to use DeOxit and a brush to clean the rotor contacts that had been greased with that old white grease. I sparingly relubed the Tuning and BS condenser ball bearings with red wheel bearing grease worked into the ball bearings ONLY.

I wondered about this white grease smeared everywhere and remembered that back in the days of TV repair shops, older TVs had a revolving turret, channel-changing Tuner. There was a product then called "Tuner Grease" that was supposed to be applied to the TV-tuner contacts. It was supposed to decrease the wear, ease the "channel-changing effort" and provide better contact. Anyway, that might have been the source for the idea of smearing the grease everywhere in the receiver.

Jan 23, 2024 - Recap Job - The parts came in today so I started the recap job. Eleven caps installed so far. It should be more but three times (so far) I've had to completely rebuild a solder joint where a replacement resistor was just wrapped and soldered with old lead just clipped. Sloppy work that needed to be corrected, so it takes a lot more time. Each replacement capacitor lead is installed inside the terminal hole. This requires removing the old capacitor lead and usually "wicking" a lot of the old solder out. Then the new capacitor lead can be installed correctly and soldered properly. Takes a lot longer but it then looks and functions like a professional did the rework (nothing looks more like an "amateur job" than using hook splices to install replacement parts.)

More caps replaced - I found that the plate load bypass on the Mixer had a replacement plastic molded cap that was 0.1uf but the value shown in the manual indicated that it should be a .05uf. Additionally, one end of the plastic 0.1uf hadn't even been soldered. This plastic cap was replaced with a .05uf 600vdc Orange Drop. The two IF amplifier screen load resistors were obvious replacements being 2W resistors. But, even these 2W resistors had swollen from being overheated by the original leaky bypass capacitors that were still in the circuit (if the original 1/2W resistors burn up,...replace them with 2W so they can tolerate the capacitor leakage current. I've actually found this many times in various rebuilds. An aversion to replacing the actual defective part, I guess.) I replaced the resistors with the correct dissipation CCs and the capacitors with new Orange Drops. There were three .0068uf ceramic disk capacitors on the suppressor grid to ground on the two RF amps and the Mixer that were removed since the suppressor grid is already grounded and these disks aren't shown on the schematic.

Jan 24, 2024 - Completed installation of all 30 of the Orange Drop capacitors. Every joint was unsoldered, cut leads removed, the terminal solder wicked out and then the capacitor lead installed and soldered. There were no "hook splices" used. I found that one original bypass capacitor on the B+ line had just one end cut. I didn't check but it's probably shorted and that was a quick way to get the receiver semi-working again (another aversion to actually replacing the defective capacitor.) I found a few joints that appeared to be totally original but the associated resistor was just tack-soldered. Makes one wonder about National assemblers during this time period, circa 1948. It was still a hectic time at National being just after the end of WWII with a completely new receiver design so minor stuff might slip by inspection, long as the receiver passed final test, which I'm sure it did. Detailed rework like this always turns up little minor issues from the past that went unnoticed since it didn't affect test performance or owner operation.

I tested the electrolytic capacitors by lifting one end and then using a capacitance meter. One of the 25uf capacitors tested at 15uf. The 10uf tested at 17uf and the other 25uf tested at 40uf. The filter electrolytic can't be checked unless it is disconnected from the choke. The choke ties the two positive terminals together and the dual unit has a common negative. In essence, the two sections are in parallel. Tested in this manner, I read 15uf which seems to indicate that the two sections are low in capacitance. However, since I've already replaced all of the paper dielectric caps, I'll go ahead and replace the five electrolytic capacitors too (since the receiver chassis doesn't look original anymore, anyway.)

Under the chassis after the recapping job. For some reason, the Orange Drops look pretty good,...well,...better than Yellow Jackets

Jan 25, 2024 - Installed a vintage two-conductor AC cord with molded plug. This allowed me to perform a test on the power transformer. I installed a #47 lamp in the S-meter lamp socket so I'd have a pilot light of sorts. I switched on the AC and the lamp illuminated indicating I had 6.3vac from the power transformer. I measured the 5vac rectifier winding and it was okay. The HV winding was about 345vac each side of CT which is okay. I left the power transformer running for about 15 minutes to see if it got hot but it remained cold to the touch, which is good.

I installed new 10uf 450vdc electrolytic caps for the filters. I didn't remove the original capacitor but I did disconnect the two positive wires on each terminal. These were then soldered together with a lacquered sleeve installed over the joint. I then connected the two 10uf electrolytics into the circuit and placed them in a way they were somewhat hidden and not obvious. Interestingly, the NC-183D changed the filter capacitor values to 40uf for each electrolytic capacitor in the multi-section unit. The three bias filter capacitors were installed in the same manner as the originals. I had to use a slightly higher value on the negative bias voltage line, the original was 25uf and I installed a 47uf 50vdc instead. The two cathode bypass electrolytics were the original values of 10uf for the 1st AF amp cathode and 25uf for the P-P 6V6 cathodes.

Unbelievably when I was looking in the parts bins for fuses and plugs, I saw a little three pin plug laying in one bin. I turned it over and it had two small diameter pins and one large diameter pin. I tested it in the NC-183 and it was a perfect fit for the audio output connector socket (that was lucky, I didn't know where I was going to find that type of plug - in the junk parts bin, I guess.)

Jan 26, 2024 - Powered Up - Tested tubes to install into the NC-183. Only about half of the tubes were good with most of the discarded ones testing far below minimum acceptable. With all good condition tubes installed, I could now power-up the NC-183 and see what other problems might be encountered. Now, I didn't have the dials installed, so I had to just guess where I was tuning but going the AM-BC band made that easy. I connected an 8Z loudspeaker to the audio output and a ten foot long wire for the antenna. I had the receiver's AC connected to a Variac so I could bring the AC voltage up relatively slowly (like soft-start) to watch the rectifier and see what would happen. To my surprise, there was a small arc inside the 5U4GB rectifier that didn't do any damage. I tapped the 5U4GB envelope and it arced again. Well, that tube might have checked good on the TV-7 but it was obviously defective. I installed a 5U4G tube that had tested good and had been with the spare tubes included in the receiver purchase. This rectifier worked correctly and I could now hear background noise coming through the speaker. I switched from Band C down to Band E which is the AM-BC band. I tuned around and heard an AM signal but it was weaker than expected. I adjusted the Trimmer and that helped a little. Then I remembered all of the grease I had to remove from the band switch. I "rocked" the band switch and suddenly the signal went from S-3 up to about S-9. The audio was fantastic sounding even though the speaker was a little eight-inch test speaker. I tuned around the AM-BC band and heard all of the normal daytime stations. I checked the B+ at +345vdc at the second filter capacitor which sounds about right. I couldn't get an output on the 500Z output but the 8Z worked fine. In checking closely I found that the soldered connection at the output transformer on the 500Z terminal was a cold solder joint,...and it looked original. Anyway, resoldering the terminal got the 500Z output working fine. Next,...the dials.
Jan 27, 2024 - Pinch-wheel Adjustments - Getting the pinch-wheel drive to work with the dials is more difficult than one would think,... especially after a complete disassembly. Thoroughly cleaning the pinch-wheel drive assemblies of all of the excess grease left the excessive clearance obvious in the tuning. Originally, National probably used damping grease but with white grease slathered on the assembly all of that grease had to be cleaned first. The excessive clearance can be compensated for with a damping grease like Nyo-gel which is a very "sticky" grease with lots of damping ability. Only the 1/4" diameter shaft through the front bushing needs Nyo-gel and then only use it sparingly.

The next issue is the height of each dial above its associated pinch-wheel. This is controlled by the height of the front frame of the tuning condenser assembly above the chassis top surface. The studs and nuts that tighten the front of the condenser assembly in place were loose when I first inspected the receiver. In tightening them, of course, I didn't have the dials installed so I didn't know if the height was correct or not. Later, with the pinch-wheel assembly mounted, then the engagement of the dial rim into the pinch-wheel is governed by the height of the front of the tuning condenser which is adjusted with the two top nuts on the two front mounting studs which sets the height and the nut under the chassis that locks the mounting in place. Unfortunately, when assembled, the pinch-wheel flywheels block access to the bottom nuts so the flywheels have to be removed before the bottom nut can be tightened. But, the compression of the pinch-wheel depends on the flywheel being mounted, so you can't test the drive unless its fully assembled. This makes the entire adjustment a little more difficult than it should be. I had to do one dial and pinch-wheel assembly at a time and set the tuning condenser height one side at a time. It's a very slight adjustment difference between the dials slipping and the pinch-wheel gripping effectively. Trial and error will eventually find the correct setting. It took me two times on the Main Tuning and four times on the Band Spread, so finding the correct settings will require a little bit of patience.

Photo right shows the tuning condenser assembly front mounting stud and "height setting" nut on the Band Spread side of the TC assembly.

Quickie Testing - With the receiver now having dials and tuning knobs (but no index fiducials since those mount in the cabinet,) I tuned around the 20M band. It was Field Day, so lots of activity. I tried 40M and also lots of activity. Tuned WWV on 15mc to get an idea of the audio response. Lots of lows in the audio are possible with strong signals but since I was using just a ten foot long wire as a test antenna, not too many strong signals. I noticed that the dials could probably stand more illumination because of their darkened condition. Since the lamps are quite a distance away from the dials, I replaced the #47 lamps with #44 lamps to get the dials a little brighter looking. The S-meter can only have a #47 since the lamp is very close to the scale. I tried a #51 round bulb but the lamp holder won't push into the back of the S-meter with the #51 installed. Next,...installation into the cabinet which is more involved than one would think. There are dial guides that have to be installed after the receiver is in the cabinet. These keep the dials from rubbing on the index fiducials. Also, the index fiducials are also adjustable from side-to-side for centering the index fiducial with the dial and the receiver position in the cabinet.

Jan 28, 2024 - Cabinet Installation and Knob Cleaning - Installing the chassis into the cabinet isn't too difficult. The mountings are the four bottom felt-cupped feet and the chassis front is pulled flush with the inside cabinet-panel wall using the dress nuts for the Phone jack, the Send-Rec switch, the AVC-MVC switch and the Radio-Phono switch. Once these are snugged-up then the back panel can be installed. This has two screws that secure the rear of the chassis to the back panel and several screws around the perimeter to secure the back panel to the cabinet. These rear panel screws are all Philip's head sheet metal screws. It's important that ALL screws and lock washers (if originally used) are installed. The cabinet rigidity depends on all of the screws being present. With the chassis mounted in the cabinet, then the dial guides are installed. These mount with two hex head 6-32 screws and external-tooth locking washers each. The guides will have two fingers in front of the dial and one finger behind the dial. The guide prevents the dial from rubbing on the index fiducial.

Dial Guide on Band Spread dial. The two center hex head screws adjust the position of the index fiducial

Knob Cleaning - I never tried this before,...but, after seeing commercials for Dawn dish soap where a little crude oil-soaked duckling is cleaned up and degreased with no ill-effects, Dawn must be a gentle soap,...or so I thought. I soaked the knobs in warm water mixed with Dawn. The knobs were in the solution about 10 minutes. When I took the knobs out, I noticed that all of the "finger gunk" was gone from the knob flutes,...and that was great. But, as soon as the knob plastic began to dry, a white film and dullness showed up. It was like the plastic had also been "degreased." I've seen this happen with phosphate-type cleaners before. I tried to remove the white color using car wax but that didn't help. What did work was to thoroughly work into the plastic "3'n'1" oil. I used a terry-cloth and short bristle brush for that part and then rubbed the oil into the plastic with another terry-cloth until completely dry. This seemed to remove the white coating quite well and the dullness was replaced with a slight sheen. I've seen the white coating show up on National plastic knobs before (not the old bakelite knobs, just the later plastic knobs) and it's difficult to remove. It wasn't the Dawn soap, but it's something in the plastic National used for its knobs from the late-forties up well into the fifties that reacts with either water or with the soap. Probably knob cleaning with WD-40 and a scrub bristle brush to get out the "finger gunk" would have worked better. I usually follow WD-40 with Glass Plus. Anyway, I won't be using a Dawn dish soap soak again unless it's a metal knob. NOTE: I wanted to replace the TONE control knob because the skirt was bent and loose. I found a correct knob to salvage off of a junk National set. I cleaned this salvaged knob with just Glass Plus and a bristle brush. No white coating developed, so Glass Plus is safe for cleaning these types of National plastic knob grips.

Jan 29, 2024 - Installing the lid isn't too complicated. There are right angle stops on the hinges that only allow the lid to go up to the vertical position. The lid has to be almost closed to insert the 6/32 screws through the rear panel. Then the lid is put up vertically and the stops will hold the screws in place. Then the nuts and lock washers can be installed from the inside of the cabinet.

This completes the rebuild of the NC-183 as far as the mechanics and the electronics (except for installing the bottom cover.) Now, I'll use the NC-183 daily for an hour or so for a few days to do a sort of "shake-down" and if no problems crop-up we'll then proceed on to the IF and RF tracking alignment. I listened today with the Collinear Array as the antenna. Even 20mc WWV was strong. Trenton Military on 15.035mc USB from Ontario, Canada was easily heard. I switched over to a Collins 270G-3 10" loudspeaker that really improved the bass response. I listened to a couple of SW-BC stations and the strong ones sound quite impressive.

Jan 30, 2024 - I adjusted the position of the dial index fiducials to exactly match the dial stops on the gear drive and the position of the tuning and band spread condensers set at full mesh. This is the preliminary mechanical set-up that proceeds any actual electronic alignment. I then checked a few frequency marker stations and I was really surprised at how close the electronic tracking alignment already was. WWV 15mc was very close and WWV 10mc was 100kc off. On the AM-BC band all of the daytime locals were very close to their assigned frequencies. The Band Spread was set to the "SET" mark at 180 of 200 on the logging scale. The receiver seems to be performing much better than I would have expected and that indicates that the alignment is probably pretty close. Even the Crystal Filter seemed to be working pretty well. When I do the alignment in a day or so, I'll find out just how close it really is. To eliminate the need of flipping through the pages of the manual for the adjustment locations, I made copies of the top chassis layout and the bottom chassis layout. These two pages aren't with the alignment procedure in the manual so having loose copies simplifies locating the correct adjustments while performing the alignment.

NC-183 Installed back in the Cabinet

NC-183  SN: 241 0262

Feb 1, 2024 - Alignments - IF - The NC-183 IF seemed to be tuned to 451kc. I "rang" the Crystal Filter crystal and it was resonant at 457.8kc, so the IF wasn't really very close to where it should be. Using 457.8kc as the alignment frequency, I connected the RF signal generator to the Mixer stator through a .1uf capacitor. The IF and Crystal Filter were aligned as specified in the National NC-183 manual. Then the Amplified AVC and the BFO were adjusted for 457.8kc. Before the IF alignment I couldn't get the S-meter to respond much more than about S-4 on 15mc WWV, now it showed S-9+, so the IF was certainly improved.  NOTE: One thing I noticed had to do with my having both the National manual and the Sam's Photofact for the NC-183. The National IF alignment has several steps specifically for the Crystal Filter alignment that pays off with its proper operation. The Sam's doesn't have a Crystal Filter alignment procedure and just instructs the technician to "peak" the adjustments in the Crystal Filter at the IF frequency. In fact, the Sam's doesn't even have the procedure to "ring" the crystal to determine the correct IF. If the Crystal Filter and IF are aligned as instructed in the Sam's Photofact the receiver will probably work okay but the Crystal Filter won't operate correctly. Use the National NC-183 manual procedure.

Alignments - RF Tracking - The RF Tracking wasn't too far off. Just little adjustments to get the dial indications to be very accurate. Since I did the mechanical set up first and apparently nobody in the past had gotten into the inductance loops for adjusting the low end, just adjusting the trimmers accurately got the entire tracking to be excellent.

Finishing Up - The bottom cover was really greasy on the side facing into the chassis. I had to use WD-40 and a brass bristle brush to remove the grease. This was followed by Glass Plus to clean the WD-40 residue. The bottom cover is mounted with three sheet metal screws at the rear, one sheet metal screw in the center and a 6-32 binder head machine screw and flat washer in front. The photo to the left shows the NC-183 after the rebuild. Note that the dials, when illuminated, look bright and the nomenclature is crisp. The red isn't as faded-looking when the dials are illuminated. The photo was taken after I did the "touch-up" paint job. The "touch-up" paint was mixed as described in Jan 18th log "Touch-up Paint" above.


NC-183 Performance After the Rebuild

Shortwave Listening - I connected the NC-183 to the Collinear Array antenna. I listened for the Chinese Maritime Stations at 16.985mc and heard XSG coming in pretty well. I didn't hear XSQ which is usually the stronger station but hearing XSG was a good sign since either one are moderately difficult stations on 16mc (on Sunday afternoon, I copied XSQ on 16.998mc about RST 579.) Listened to a few SW-BC stations in the 19M band and the 31M band. I then went to 39M and the SW-BC stations were extremely strong almost pegging the S-meter. At 49M, only Radio Havana seemed to be really strong but there was one station that pegged the S-meter that must have been a Westcoast USA SW station (religious BC.) Went to 80M and some of the SSB stations required reducing the RF gain to "2" they were so strong. Since I was listening to SSB, I had the receiver in MVC and throttled-back the RF gain for proper demodulation. There were two AM stations on around 3870kc but they were not very strong but still could be copied Q5. I was listening around 1700hrs PST. Audio response is fantastic on SW-BC, if the station is actually broadcasting good audio (some shortwave stations don't.) I did notice that on extremely strong SW-BC stations slightly better bass response can be realized by going to MVC then reducing the RF gain and increasing the AF gain. In AVC, with the RF gain at 9.5, these SW stations have very nice, broad audio frequency response although many of the moderately strong stations are affected by QSB. I'm using a Collins 270G-3 loudspeaker, so I might find even better audio results from using a more "hi-fi" speaker (I'm presently setting-up up a large corner wall-mount housing that has a bottom bass reflex port. It's using a 12" loudspeaker and it sounds pretty nice setting on the floor.) The NC-183 is an excellent SWL receiver.

Ham Operation - I've paired the NC-183 with the Johnson-Viking 1 transmitter. They are both approximately from the same time period, 1949 to 1950. The antenna is the Collinear Array. I had to set-up a DowKey relay to work with the Viking 1 relay drive that is parallel with the Plate switch and then to use the DowKey auxiliary contacts to operate the remote standby on the NC-183. The Viking 1 transmitter doesn't have push-to-talk so turning ON the PLATE switch places the transmitter into operation and via the DowKey places the NC-183 in standby. The DowKey T-R contacts switch the antenna to the Viking 1 when the PLATE is turned on. This particular DowKey has the spring-loaded disconnect in the receiver-side coaxial fitting barrel as added protection.  >>>

The Viking 1 with VFO and the NC-183 station

>>>   I operated this station for the Nevada Vintage Mil-Rad Net on Feb 4, 2024. The NC-183 operation was flawless, excellent performing receiver. I had to reduce the RF Gain down to about 7 and the AF Gain was at 2 for the entire net since propagation was great and all signals were very strong. Even with the RF gain at 7, the S-meter would generally show stations as S-9+30db and the ambient noise level was S-3 with that set-up using the Collinear Array on 3.974mc (0730hrs to 0900hrs.) I used the Crystal Filter one time and it was effective on position 3 with a slight Phasing adjustment to eliminate some temporary SSB QRM (proper alignment of the Crystal Filter makes it an extremely useful tool in combating QRM, even in the AM mode.) The rest of the net was received with the Crystal Filter switched out. I was still using the Collins 270G-3 speaker and most of the time had the Tone set to "3" for excellent audio response. The conclusion is that the NC-183 can perform very well as a vintage station receiver on 75M. 40M doesn't have very much AM activity. I only hear a station or two, once in a while, up around 7.295mc. I don't think using the NC-183 on 40M would present any problems, especially if 40M CW was used for the operations. There hasn't been any activity on 20M AM in years. Bob K7POF used to have a daily AM net on 14.267mc but that was almost 30 years ago. Nowadays, 20M CW operation would be a possibility. On 10M AM it's difficult to tell if you're having a QSO with an actual licensed ham unless you can check QRZ during the QSO (and even then you don't know if the callsign isn't being "bootlegged.") I haven't operated 10M in over 20 years because of that type of problem. To conclude the ham operation review, the NC-183 is an excellent vintage receiver. It's easy to set-up the remote standby. The sensitivity is very good and the selectivity can easily cope with any of the normal QRM.
Conclusion - Introduced during that post-WWII time when a lot of communication receivers were being produced that were either repackaging of pre-WWII designs (or actual WWII designs,) the NC-183 Series of receivers were designed with a different end-user in mind - the SWL that might also be a budding audiophile or maybe even a discriminating radio amateur. With a front-end design that was up-to-date with the late-forties technology coupled with what was then considered "powerhouse" audio, the NC-183 was a different type of receiver that could provide enjoyment for several different types of users. The NC-173 was a "true ham receiver." Maybe a little less sophisticated but still it was a capable receiver in the right hands,...a radio amateur. A few years later and with many changes in ham radio operation and conditions the NC-183 underwent a major redesign to become the ultimate in the receiver concept. With double-conversion, triple IF amplification and high fidelity audio, the NC-183D is still the "vintage receiver of choice" for the AM ham operator that really wants to enjoy listening to that "AM sound" and still be able to cope with all of the modern day ham band reception issues. Luckily, finding a really good condition NC-183D isn't too difficult. Most of the "D" receivers seem to have endured time quite well and with a proper rebuild and alignment they can still provide top performance no matter what your particular radio reception interests happen to be.  References


1. Manuals for NC-183D and NC-183

2. 1950 ARRL Handbook National Co.,Inc. advertising

3. Communications Receivers 4th Edition, Ray Moore


1. BAMA Edebris - manual NC-173

2. National Co., Inc. - advertisements for NC-173, NC-183 and NC-183D


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