Radio Boulevard
Western Historic Radio Museum

 
WHRM Radio Photo Gallery
 

Post-WWII Ham Gear
 

 Amateur Radio Receivers
 and
Amateur Radio Transmitters
 

- 1946 to 1958 -
 

I1LOV, Augusto Lovisolo, Varese, Italy  (ca:1958) with Collins KWS-1 and 75A-4  (photo from his QSL card.)

National Company Inc.  -  HRO-5A1 

At the end of WWII, most manufacturers had been building for the war effort since 1942. They didn't have anything new or ready for production for the 1946 model year. National offered the WWII version HRO-5 in late-1945 as their new table model receiver. The HRO Senior had evolved through WWII but by the end of the war, it still didn't look very different than the old pre-war receiver. The major changes during the war involved the crystal filter design, the changeover to metal octal tubes, a new non-ventilated cabinet and the use of mostly JAN parts. These late-WWII receivers were designated as the HRO-5 and the HRO-W. The first HRO-5 receivers offered after WWII were models that didn't have the bandspread coil sets. In a short time period (probably by 1946,) bandspread was added to the A, B, C and D coil sets and the receiver designated as the HRO-5A. As with the late-WWII coil sets, the post-war coil sets used a single aluminum plate with silk-screened graphs. Many of the HRO receivers sold by National in the early post-WWII period will have several variations that seem to confirm that National was trying to "clear out" old stock. Many post-WWII HROs will be found with pre-WWII S-meters installed. Several front panels have turned up with extra holes for the long data plate used on the HRO-W. Expect to find many variations when examining HRO-5 receivers sold up to about mid-1946. By mid-1946, the HRO-5A1 replaced the HRO-5A and added a noise limiter to the circuit. When the receiver was in a table top cabinet it was designated as the HRO-5TA1 (rack mounts were HRO-5RA1.) The HRO-5A1 used 12 tubes - two additional tubes were necessary for the noise limiter circuit. Early versions of the HRO-5A1 may be found with the round S-meters, earlier surplus front panels which will have the National HRO-5A1 tag mounted just above the Noise Limiter control and many other minor variations that show that National was still trying to clear out old stock. The last of the HRO-5A1 receivers will have a square S-meter, cadmium-plated chassis, a stepped-switch Crystal Filter Selectivity control and rubber insulated wire under the chassis in the wiring harness. The late versions of the HRO-5A1 receivers seem to be consistent in construction and use of new parts and components. The HRO-5TA1 shown in the photo above is a very late example with a production run code of 184.

In late-1946, an HRO-6 was produced in a very small production run that used the same numerical designation as the HRO-5A1 production run, 184. It appears identical to the HRO-5A1 externally and the only difference between the two receivers is a slight change to the Noise Limiter circuit. It's likely that the actual change in the Noise Limiter is that it was build directly onto the chassis instead of being built on a small chassis that was mounted on top of the receiver chassis. It's possible that National designated the HRO-5A1 receivers built after July, 1946 as the "HRO-6" for a short time. Considering that the ham consumers might assume that the HRO-6 would be National's "new 1947 model" and that National was actually doing the design work for the HRO-7, the HRO-6 designation was quickly changed back to HRO-5A1. National apparently didn't want the hams thinking that their new receiver looked just like the pre-WWII HRO receivers.

For 1947, the HRO-7 was introduced and this receiver totally changed the appearance of the black wrinkle finish HRO. The HRO-7 was light gray smooth finish, the cabinet was modernized with rounded corners, the S-meter was mounted behind the panel and viewed through a cut-out and the knobs were restyled. The matching speaker was also restyled to match the new HRO-7's appearance. Internally, a voltage regulator was added and the LO changed to a 6C4 miniature tube. Coil sets were changed to not employ handles for removal and levers were utilized. Additionally, the graphs and charts were replaced with a linear calibration scale. Although the physical appearance of the HRO-7 changed dramatically, internally most of the updates to the HRO-7 rather conservative.

the Hallicrafters, Inc.  -  S-38 Series

The S-38 was a post-war continuation of the "introductory" type receiver line, characterized by the pre-war Sky Buddy series. Intended for the beginning ham or shortwave listener, the S-38 was low-priced, easy to operate and most users were able to get good performance results considering the receiver's circuit limitations. Introduced in 1946, the initial S-38 had six tubes with Bandspread, BFO and Noise Limiter circuits. All of the S-38 series receivers were AC-DC operated. Shortly after its introduction, the circuit was changed to a five tube set with no noise limiter and a CW position that actually set-up a regenerative oscillation in the IF. Versions A, B and C have semi-circular dials while the D and E versions have slide-rule dials. Selling price was around $40 in 1946 but by production's end, in 1961, the price had climbed to $55.

the Hallicrafters, Inc.  -  SX-42

The SX-42 was introduced in mid-1946 as the post-war successor to the company's former "flagship" - the SX-28A. The SX-42 was a complete departure from the usual receiver styling of the time. Well-known industrial designer Raymond Loewy created a receiver exterior that didn't look like any piece of radio gear that had proceeded his futuristic, award-winning design. The main tuning escutcheon with its green tinted plastic and green main tuning dial resembled something from under a then modern jet canopy. A coaxial tuning system allowed the user to "lock" either the main tuning or bandspread tuning depending on which was going to be used. Besides the ultra-modern exterior, the receiver circuit boasted a very wide frequency coverage of .54 to 108MC with the addition of Frequency Modulation capabilities from 27 to 108MC. The receiver used 15 tubes like its predecessor the SX-28A did but a Converter tube is used rather than separate LO and Mixer tubes. Additionally, a VR tube was included along with Limiter and Discriminator tubes for FM. The SX-42 was single-conversion with double pre-selection on all bands (except band 1, AM-BC) using two seven-pin miniature tubes for RF amplifiers (6AG5 tubes.) Four Loktal type tubes were also used in the circuit and the remaining nine tubes were standard Octal types. The audio circuit used P-P 6V6 tubes and provided 500Z ohm and 5000Z ohm outputs. Selling price was $250 but, by 1947, the price increased to $275. There were several matching speakers available but the R-42 table-top bass-reflex speaker is generally pictured with the receiver in Hallicrafters' advertising. Another accessory was a table top "Tilt-Mount" on which the receiver was placed. The Tilt-Mount then allowed the entire receiver position to be moved in any angle to allow a comfortable view the receiver front panel. Early versions of the SX-42 will have a greenish colored bezel on the bandspread dial and a black background "h" emblem on the dial. Later versions have a light gray bezel on the bandspread dial and a silver background "h" emblem. The are a multitude of engineering upgrades to the circuit and manufacturing process all through the SX-42 production.

The SX-42 was really never a very popular receiver with hams. Certainly the expense of the receiver was an important issue for many but its unusual looks, which hams may have been considered "too modern" in the then age of "wrinkle finish black panels," may have also been a factor. The coverage of the then new FM band (88 to 108MC started in 1946) may have made hams feel that the receiver was more of an expensive luxury for the well-to-do consumer than for a typical budget-minded ham. At any rate, production of the SX-42 was stopped in early 1948 - a fairly short lifespan for a "flagship" receiver. The SX-62 took the SX-42's place as the high-end Hallicrafters receiver but it seemed to again be more for the consumer market and few hams bought them as their station receiver. The popular SX-71, certainly designed for hams, filled in that portion of the ham communications receiver market after the demise of the SX-42. Today, the features that resulted in the SX-42's only moderate success are what attract collectors to the receiver - the futuristic styling (which won an International Design Award for Raymond Loewy from the NY Museum of Modern Art,) the wide-swing FM-BC coverage, the fabulous audio (when using the proper Z speaker) and the receiver's scarcity all contribute to the SX-42's desirability. Additionally, the SX-42 is featured in a plethora of late-forties "B" movies, from Gene Autrey shows to low-budget science fiction movies, so SX-42 fans can regularly spot their favorite receiver in a multitude of film backgrounds. Shown in the photo to the left is a later version of the SX-42 along with the matching R-42 bass reflex speaker. This combination was purchased for K6HUZ by his father as a special gift for passing the General Class license exam. It was 1954 and the SX-42 and R-42 were found in a pawn shop not far from the Federal Building, where the FCC administered the amateur exams, in downtown Los Angeles. K6HUZ kept the receiver and speaker in great condition for 57 years, then donating it to our museum. The photo above in the header shows an earlier version of the SX-42. I found this receiver in a backyard shed in Carson Valley, Nevada. It had been the victim of poor troubleshooting and had several modifications to the circuit trying to correct a fundamental mis-wire that happened when the filter capacitors were replaced. I had to strip out the IF section of the receiver and rebuild it to stock. I went ahead and fully re-capped the receiver. It now works fabulously with great audio and respectable sensitivity. I have yet to have the "gun metal dark gray" paint matched so I can restore the cabinet on this early version SX-42

Collins Radio Co.  -  75A-1 

Art Collins began selling amateur transmitters in the early thirties. High quality and great performance brought in commercial and military customers making Collins Radio a major supplier of radio equipment during WWII. Collins entered into the communications receiver market after WWII with a double conversion superheterodyne receiver that was entirely permeability tuned. Using a precision Permeability Tuned Oscillator (called a PTO - Type 70E-7) along with a multiple crystal controlled oscillator and by keeping the maximum coverage of each band to just 1.0 MC, Collins was able to achieve 1.0 KC accuracy in the dial read out with receiver stability that was incredible. The linear dial system features "band in use" illumination and requires twelve #328 lamps - two lamps for each band. The 75A was an introductory model that was probably not produced in any quantity. It was superseded by the 75A-1 in 1947 - the only noticeable difference was the addition of a Noise Limiter circuit with a front panel switch. Though the 75A-1 is a 1947 design, the receiver's performance is a pleasant surprise - more like a receiver from the 1960s with impressive stability, dial accuracy, sensitivity and selectivity. The 75A-1 is a first-class receiver for a vintage ham station with performance that is still competitive, even on 10 meters. Audio in the AM mode may be considered somewhat restricted due to the 75A-1's excellent selectivity but, after all (using the CCA argument,) it is a communications receiver.

Collins Radio Co.  -  32V-2

The 32V-2 transmitter was introduced in 1948 and had some improvements over its predecessor, the 32V-1. The new transmitter redesigned the Pi-network so that it could be fully adjusted with the front panel controls. The V-1 design required lifting the lid to access the loading adjustment. There were other minor improvements to the power supply and regulation during the production of the V-2. The transmitter uses a PTO and multiplier stages to create a tracking exciter that allows the transmitter to stay "in tune" as the frequency is changed. All that is required is for the operator to set the frequency and then "match" the transmitter output to the antenna. Other than the Pi-network, all circuits are automatically tuned as the tuning dial is adjusted. The system used the typical Collins coil-slug rack carriers and full permeability tuning is used throughout the oscillator and multiplier stages. The frequency readout is Collins-accurate. Most 32-V transmitters do require a bit of work on the "band-in-use" slide rule dial as the illumination (using the ten #328 lamps) is problematic. Also, usually the white plastic backing of the slide rule dial needs to be replaced for first-class appearance. A built-in sidetone oscillator is provided in the CW mode and a PTT function is included for AM. The transmitter is stoutly built and weighs in at over 100 lbs. The PA tube is a Raytheon 4D32 with selectable plate voltage - either 600 or 700vdc -  the lower voltage allowing the 4D32 to run at the manufacturer's specifications for continuous duty. The modulator tubes are 807s. The power output is generally around 100 watts. If the 32V-2 is conservatively operated, it is virtually indestructible. A really fine transmitter that is easy to use, reliable, ample power capabilities and allows high quality audio in the AM mode and a very stable CW mode. The 32V-2 was replaced by the 32V-3 in 1952.

National Company, Inc.  - HRO-60R

Introduced in 1952, the HRO-60 was the last of the evolution of tube-type HRO receivers from National. The power supply is built-in but, to the last, National retained plug-in coil assemblies and the famous micrometer dial (it wouldn't have been an HRO otherwise.) The HRO-60 is double conversion above 7MC, has two RF amplifiers, three IF amplifiers and P/P audio output using 6V6s - 18 tubes in all. The selling price was high at $480 but by production's end, in the early sixties, the price had escalated to nearly $750! Coil assemblies were available for frequency coverage from 50-430KC, 480KC-35MC and 50-54MC. The linear dial uses removable plastic scales that are mounted to a rotatable drum for single band-in-use readout. Two accessory sockets are provided for the optional NBFM adaptor and optional 100KC-1MC Crystal Calibrator. Shown in the photo is the unusual HRO-60R, a rack mount version that included the MRR-2 table rack and the SC-2 speaker panel featuring storage for extra coil assemblies behind the doors.

Some Ham AM ops consider the HRO-60 receivers inferior in performance when compared to the earlier HRO-50 (single conversion, two IF amps) though this opinion is usually based on the audio response which is more restricted on the HRO-60 due to its increased selectivity. The HRO-60 (and the HRO-50-1) used two "double" IF transformers to increase the passband selectivity and added an extra IF stage of amplification compared to the earlier HRO-50. The HRO-60's increased IF selectivity was necessary due to the crowded band conditions of the fifties. Another issue with the HRO-60 is the alignment instructions contained in the National manuals. Many HRO-60s are incorrectly aligned due to the confusion of at least two different first conversion oscillator frequencies used at various times during production. National published at least two different manuals with different first conversion oscillator frequencies, 1990KC and 2010KC. Also, hand-written in one of my original HRO-60 manuals says "1995kc - per National" which appears to have been an owner notation based on a response to a question to National. Generally, the early version HRO-60s use 2010kc and the later versions use 1990kc. When aligning this particular section of an HRO-60, use a specific amplitude input signal for alignment and accurately measure the receiver output. Try both frequencies using the same level input signal. You should find that one frequency or the other provides slightly higher output which would be the proper first conversion frequency for that particular HRO-60. When meticulously aligned, the HRO-60 has tremendous sensitivity with low noise, impressive selectivity (QRM is rarely a problem) and "respectable" audio from the P/P 6V6s. Due to the lack of a true speaker enclosure, all rack mounted HROs sound a little "thin" when used with the SC-2 type of speaker panel.

I've owned this particular HRO-60R twice. The first time was in 1990 when I purchased it from a ham in New York state. It was shipped to Nevada and I set-up the HRO-60R to run with a Johnson 500 I had at the time. After a couple of years, I traded the HRO-60R to NU6AM for a really nice National FBX receiver with the band spread coil sets. Sometime later, NU6AM traded it to K6DGH who in turn sold it to KG6YV. All of the trading and selling took place over a period of several years. Around 2003, I asked NU6AM if he knew the whereabouts of the HRO-60R. Jim told me that as far as he knew Greg, KG6YV, still had it. A telephone call to Greg set up the deal and a trip down to California was made for the pick up. I couldn't believe that after ten-plus years absence, I was able to find my old receiver so close by and was able to purchase it back. I now use the HRO-60R as the station receiver with the Johnson Desk KW.

If you want a good laugh and happen to have some older issues of Electric Radio magazine, check out the cover of ER issue #27 - July 1991 - for a photo of this HRO-60R shown above along with your's truly, WA7YBS. If you don't have issue #27 and still want a good laugh, CLICK on:  ER Cover Boy

The E. F. Johnson Company has been in business since the 1920s and is still active in the component business. During the post-WWII period up to about 1974, Johnson was a major builder of ham transmitters, ham accessories and other communications equipment. The Viking Navigator was introduced in 1957 and was available for about four years. It could be purchased as either a kit or fully assembled. The transmitter-exciter is only 40 watts input power with a little over 25 watts of output power on CW only. Coverage is 160 meters through 10 meters. The PA tube is a 6146 with about 400vdc on the plate.

The Navigator featured a fairly standard Johnson VFO, although regulation is somewhat different than their standard VFO as found on the Ranger, for example. Also, a keyer tube is used which provides adjustability of the CW keyed waveform shape. The "Iron Vane" meter is a source of many problems and its accuracy is always in question. The slide switch that selects Grid or Plate current is also somewhat problematic. Many times, Navigators are found with these two parts replaced. A great QRP CW transmitter that is very small and light weight. Original selling price was $199.50 wired and $149.50 as a kit. Only 840 Navigator transmitters were produced. The Navigator shown was donated to the museum by K6QY.

When operating a Navigator as a CW QRP transmitter, the "Iron Vane" meter is constantly "banging" against the zero-stop. Sooner or later, this must have resulted in the meter needle breaking off and ruining the meter. That's probably why nowadays so many Navigators have replacement meters. It's very easy to install a jumper across an original meter's terminals to protect the meter and then use an external watt meter to load up the transmitter. A defective original Navigator meter will be next to impossible to replace so this easy protection assures a functional original meter will survive indefinitely.

That being said, I can't stress the point strongly enough that the original Johnson Navigator "iron vane" meter is a real "piece of junk" and is not really repairable if a problem develops in an original unit. The plastic cover is glued all around the perimeter of the meter scale backing plate and any attempt to cut away the glue cracks or breaks the plastic cover. Apparently, if a problem developed in the meter, Johnson wanted you to replace the entire meter instead of repairing it. That might have been okay in the late 1950s but now, 50+ years later, I don't think Johnson still stocks Navigator meters. I think it would be possible to fit a Johnson Ranger meter to the Navigator and that would then become an accurate and useable instrument which the original Navigator meter never was. 

E. F. Johnson Company -  Viking Desk Kilowatt, Viking Ranger, Viking KW Match Box

The Viking Desk KW was introduced in 1955 and was available up to around 1964. The "Desk" is a high power RF amplifier with a high power audio modulator, power supplies and all of the control equipment built into a fairly compact "pedestal." The Desk KW features continuous tuning from 3.5 to 30mc. The PA operates Class C and has two output levels, low power for tuning up or operation at 250 watts carrier output or high power for 1KW input power. Plate voltage is either 1300vdc or 2600vdc depending on the output power selection. Originally, 872 MV rectifiers were used for the Plate supply but many amateurs have replaced these with 4B32 Xenon rectifiers or with Solid State rectifiers. An external relay (operated by the exciter) must be used with the Desk KW for linear operation for SSB to allow switching between "Blocking Bias" and "Operating Bias." The PA requires 30 watts of drive for full output and the modulator requires 15W for full audio drive on AM. The PA tubes are a pair of 4-250A tubes (4-400 on later Desks) modulated by a pair of 810 tubes. The entire unit is on guides and rollers and is easily accessed for testing or adjustments. The desk itself was a $123.50 option that could be bolted to the side of the pedestal for complete operating station desk with room for the exciter and the station receiver. The Desk KW sold $1595 without the desk. The Desk KW shown is number 280 of the 402 built.

The Viking Ranger was a 75 watt CW or 65 watt AM exciter-transmitter that covered 160M to 10M and had a built-in VFO that was very stable. The audio section featured a special modulation transformer with a winding that was used for negative feedback resulting in excellent quality audio. The PA tube is a single 6146 and the modulator tubes are a pair of 1614 tubes. The Ranger had all of the outputs accessible to interface with the Desk KW for sufficient drive for full output from the Desk KW. Generally a small attenuator is inserted between the Ranger RF output and the Desk KW input to allow better adjustment of the Ranger's drive and output circuits. Rangers were very popular as a stand-alone transmitter also, especially for Novices since the power limit then was 75W on CW only, crystal control (you got to use the VFO after you up-graded your license.) Still today, the Ranger is a popular transmitter for vintage AM because of its excellent audio and "bullet-proof" construction. Over 14,000 Rangers were built. They were available as either a kit or fully assembled. Prices were $293 assembled or $214.50 as a kit. The later version was designated as the Ranger II and featured different modulator tubes, a two-tone gray paint job and dropping the 11M coverage in favor of 6M coverage.

The Viking Match Box was a heavy duty, balanced antenna coupler that was link coupled, used bandswitching and had two split-stator variable capacitors that allowed matching various kinds of antenna loads to a transmitter. The Match Box was specifically designed for balanced antennas but could also match coax fed loads or end fed wires. The SWR bridge required an external Directional Coupler to function but the Match Box was available without the SWR bridge option in which case there is no meter installed. A built-in antenna relay is included inside the box with access via an external terminal strip mounted on the rear of the unit.

The Viking Desk KW shown was partially disassembled and was going to be "parted out" by the University of Nevada (in 1997.) A friend of mine that worked at UNR saw the Desk KW (disassembled) in the hall on the second floor of the Electronics Building. His phone call to me was something like,... "you interested in a Johnson Desk KW? Well you better get over here, they're throwing one away." When I got to the Electronics Building, I found the Desk KW apart and looking like it was destined for destruction. I asked around and finally found that the Wolf Pack Ham Club had gotten the Desk as a donation and they weren't sure what to do with it since they couldn't move it to the third floor where their ham club station was. I made a deal with them of cash for some equipment they wanted to buy and then the Desk KW was on its way to Virginia City. The KW Matchbox was included in the deal. I rebuilt the Desk KW and it is now fully operational and usually on the air on the Saturday Morning West Coast AM 75M Net (8AM Pacific Time, 3870 KC.) The Viking Ranger was the XYLs Novice transmitter back in 1975. We've always kept it in operational condition. Several years ago I replaced all of the aging capacitors. Other than increasing the wattage rating of the regulator resistor (but not changing its proper location in the VFO) no mods are installed  - Rangers sound very nice with stock audio.

One of the main problems with the Desk KW is that it was wired with solid conductor wire which has a real tendency to break when moved. Of course, Johnson thought you'd never be moving the harness around but you have to when going through the transmitter. Keep an eye on the wires while doing any rework as you're sure to break at least one wire during the process.

The four fans used in the Desk KW are also problems. The two main fans "push and pull" the air through the Desk chassis to keep everything cool. These open frame fans don't last forever and many have been replaced over the years. There are exact duplicates of the fan motors still available and many suppliers stock them. Reuse the original fan blade and be sure that you have the lower fan pushing air in and the upper fan blowing air out. The originals should be serviced every year or so. Oil the felts by saturation with light machine oil.

The Desk KW chassis rolls out but only so far until you are going to have to support the front. I use a $12 dolly that you can find at Home Depot or many other hardware stores. The dolly is placed under the Desk chassis and as you pull the chassis out you move the dolly more to the center of the chassis until the chassis is entirely out of the pedestal. Then you'll have a way to roll the chassis around for easy access to all areas. The chassis weighs close to 200 lbs with all of the iron installed, so the dolly helps a lot. When re-installing the chassis into the pedestal, I use a lever (a five foot long piece of 3/4" pipe) to lift each back edge of the chassis into the pedestal. Once both edges are in, then it's easy to push the chassis back in on the internal rollers.

I use 6156 tubes in the final PA because these RCA versions of the Eimac 4-250A are usually cheaper but have the same specs. The only difference is the 6156 doesn't have the metal base shroud to direct air flow around the tube. Since we only run the Desk KW in the "Tune Mode" it is never really running more than at just "an idle" and therefore the 6156s work fine. I also don't use the original 872 MV rectifier tubes but use 4B32 Xenon rectifier tubes.

photo above: Output Network with over-sized roller inductor and large air variable capacitor. Photo right: The finals - a pair of 6156 tubes which are the RCA equivalents of Eimac 4-250A tubes

photo above: The modulator section showing the pair of 810 tubes and the huge modulation transformer.

Central Electronics, Inc. -  100V Multiphase Transmitter

Central Electronics was founded by Wesley Schum W9DYV in the early 1950s. Their main products were phasing-type SSB transmitters-exciters, although some SSB-oriented receiving devices and monitoring equipment also were produced. Around 1958, Zenith Radio Corporation acquired Central Electronics. At about the same time, CE introduced the 100V transmitter. The design was by Schum and engineer, Joe Batchelor. Initially, several minor problems caused delays in delivery of the first 100Vs produced. Dealers were sent the first 100Vs to help promote the transmitter by actually using them on the air. Selling price was around $800. Eventually, around 1500 100V transmitters were produced before the 200V was introduced in 1961. About the same time, Zenith began to institute cost-cutting measures and eventually, in 1962, closed down Central Electronics due to low profits for Zenith.

The CE 100V design uses a phasing-type of approach to sideband suppression. In addition to USB and LSB, DSB-SC, AM, PM, FSK and CW modes can be selected. Unique to the CE 100V is the broadband output section that allows the operator to select a frequency and begin transmitting - no antenna loading or tuning is required. The broadband circuitry does require that a low SWR be presented to the transmitter output and an illuminated indicator warns the user if the SWR is too high. Most of the controls are located under the two doors on the front panel. These were considered "set and forget" type controls. A two-speed VFO tuning control allows very fine adjustment of the frequency. A monitoring CRT was provided and displayed a trapezoid pattern when the transmitter was properly adjusted. Typical output power was 100W PEP although the output was continuously adjustable down to 10W.

Today, the CE-100V is still a popular transmitter because of its versatility, excellent audio capabilities and incredibly ""good looks."

Collins Radio Co.  -  75A-4 

Considered by many radio amateurs to be the finest "ham bands only" tube-type receiver ever produced. The Collins 75A-4 was introduced in 1955 and manufactured up to about 1958 or so, with around 6000 total production. The 22 tube circuit featured a 3.1 kc mechanical filter and a product detector, making the 75A-4 ready for SSB - but it could also copy AM quite well since a separate AM envelope detector was also provided. For better AM copy an optional 6.0 kc mechanical filter could be purchased or, for CW, an 800Hz filter was available. Later, other filter frequencies were offered, e.g., 500 cycle for CW, 2.1 kc for SSB, plus others. Up to three mechanical filters could be installed, providing optimum selectivity for CW, SSB or AM. Frequency readout was "Collins accurate" and sensitivity was competitive. Audio was little better than communications grade. The 4:1 vernier knob was an early option that allowed for very smooth tuning and the later models had it installed "from the factory."  Earlier models had a fairly high hum level and problems with the AVC. Collins installed up-grades rather early in production to correct these problems, although there were many upgrades from Collins through most of the 75A-4 production. Collectors favor the later serial numbers (higher than 4000) since all up-grades were in place by that time. However, Collins offered service bulletins and up-grade kits which many owners installed themselves, so serial numbers alone do not tell you the performance capabilities of a particular 75A-4. Shown above is 75A-4 sn875 (with all up-grades.) I purchased this 75A-4 in April 1970 and it has been "paired" with a matching KWS-1 (sn616) transmitter since December, 1970. For the past 40 years, they have been my regular SSB/CW station.

Collins Radio Co.  -  KWS-1

The KWS-1 was an incredible transmitter when it was introduced in 1955. At a time when AM dominated the voice mode of communications, Collins introduced a high-power SSB transmitter that was so expensive, nobody could afford it - $2100. Everything about the KWS-1 is first-class. The construction was military-grade, the components first-rate and the design was "cutting edge" for 1955. Total production was around 1600.

The KWS-1 is capable of 1KW SSB transmission utilizing a 3.1kc mechanical filter and balanced diode-ring modulator to create the selectable USB or LSB signal with suppressed carrier. Further mixing in various stages coverts the signal to the proper output frequency. It is then routed into the Class AB-1 Linear Amplifier comprised of two 4X150 external anode, air-cooled tubes run in parallel (now 4CX250Bs.) Plate voltage is 2KV. The power output of a properly operating KWS-1 is around 650W DC. In the AM mode, the carrier is re-inserted but the signal is still kept in a single-side band mode. Operating a KWS-1 in the AM mode will usually foment some negative comments from "strict DSB AMers" but, unless mentioned, many never notice that only one sideband is being transmitted. Since AM is a 100% duty-cycle mode, the power has to be reduced to about 400W input. In the CW mode a full 1KW can be utilized since the duty-cycle is usually around 50%. Due to the 3.1kc mechanical filter, the KWS-1 sounds incredible on SSB today since most hams are used to hearing rather narrow SSB (2.1kc) and generally a QSO will garner positive comments on the audio.

The KWS-1 power supply is contained in the larger floor mount pedestal. Originally, a pair of 866A MV tubes were used as rectifiers but most have been replaced with 3B28 HV rectifiers or some even go SS rectifiers (I use 3B28s.) The regulated screen voltage is adjustable and so is the plate voltage to a certain extent (you can move the connections to different taps on the plate transformer.) The squirrel-cage blower is also mounted in the base of the pedestal. It is fairly noisy (bearings should be lubed every few years) and the air output is routed through a 2" diameter radiator hose (for lack of a better description.) The 2KV plate voltage is run through a cable made from RG-58U and the connector on the RF unit is somewhat problematic in its ability to stay connected. The remaining power is routed through a flexible cable with rectangular Amphenol multi-pin connector.

I purchased my KWS-1 SN:616 from K6RIM, Al, in December, 1970. Al had purchased the KWS-1 used in 1960 from Amrad Electronics in Burlingame, California (later Ham Radio Outlet.) SN 616 has been my main transmitter for many years and has proven to be a super-flexible unit capable of high power SSB and CW with reduced power AM and RTTY communications. The KWS-1 is mostly original with only routine maintenance having been performed over the years. I did have to repair a broken flex connection on one of the roller inductors a few years ago, also a broken wire in the microphone connector. Lately, I've been using the KWS-1/75A-4 on AM on the West Coast Military Radio Collector's Net where it provides a unique type of AM for enthusiasts to hear - one sideband with carrier. The KWS-1/75A-4 have a long association with military MARS stations and, of course, the SSB promotion that involved the Air Force in the mid-fifties. The KWS-1 is certainly one of the best from the "Golden Age of Ham Radio."