The kilowatt SSB transmitter the made history.


This is a very nice example of a KWS-1 RF deck. There are several flaws in the photograph that are not on the transmitter itself. Namely, the blue lines and white "flecks" in the picture are artifacts from scanning snapshots. When I get a good digital camera, I'll get some really nice shots. Anyway, this transmitter is nearly flawless and as far as I can tell, it even has the original 4X150 output tubes. It has not been electrically restored and yet, even after more than 43 years, it still produces the smooth, rich audio the KWS-1 is famous for.

One of the reasons the KWS-1 produces such mellow SSB is the relatively wide 3.1 KHz mechanical filter used in the sideband generator. The wider bandwidth permits a wider audio bandwidth. Sideband selection is the same mechanical system used in the 75A-4. However, instead of passband tuning, there are detents at the proper settings for upper or lower sideband. The sideband generator and thus the mechanical filter has a center frequency at 250 KHz instead of the 455 KHz units used in the receivers.

Collins engineers though of just about everything when they designed the KWS-1 and 75A-4, but they didn't design in transceive operation. It was little (or big) missing features that always made me wonder what went on back in the engineering labs when these rigs were developed. For example, how could Collins have built a magnificent receiver like the 75A-4 and make major mistakes in the AGC system. Ditto for the noise limiter. They built an SSB/CW system and the ANL didn't work on anything but AM. Any why didn't they spring for a little better audio output transformer in the 75A-4 along with trimmer capacitors on the mechanical filter? But, they created a magnificent RF feedback and neutralization system which produces SSB with distortion products so low that I don't think there is a single rig made for amateur use that can approach the KWS-1's better than - 40 dB distortion products.

All of the engineering consistencies aside, the KWS-1 is an example of technical and mechanical excellence. In a single box is an SSB, CW, and AM generator, the excellent PTO frequency control, and a 1000 watt input linear amplifier. Remember, in 1955, 1 KW was the legal limit. I must admit that by today's standards, the transmitter drifts more than we would like. However, at the time it was considered quite adequate, though not as stable as the 75A-4. The reason is all the heat in that small cabinet enclosure. After an hour or two of operation, the PTO case is nearly too hot to touch. Still, if you allow the rig to warm up for half and hour, the drift will be only a few hundred cycles per hour. Since the matching 75A-4 is dead stable, a little transmitter drift gives you something to do during long QSO's or nets. I just consider it part of the personality of the rig.

One feature I especially like about the early model KWS-1's like this one is the front panel mounted ALC control. That is a handy feature, especially for a transmitter with a built-in linear amp. It gives you lots of control over signal compression and permits adding a little extra punch to the signal. Of course, you really need a monitor scope to assure proper adjustment of the ALC control. That could have been a problem back the 1950's because there were no matching monitor scopes. Monitor scopes were a Heathkit speciality that didn't make the scene for several years.

I suppose I should mention the power supply. The KWS-1 was a departure from previous thinking in just about every way but the power supply. It's big. It's heavy. With a combined weight of nearly 250 pounds (KWS-1 and power supply), the power supply is reminiscent of quality AM rigs. The transformers are BIG. The chokes are HUGE. The screen voltage supply is fully regulated, not with simple gas tubes (OA2's for example) but with a full featured, precision multiple tube series regulator. A stiff power supply, highly regulated screen voltages on the output stages, combined with RF feedback, proper multistage neutralization, and an effective ALC circuit all added up to a rig that was the lever that lifted AM off its pedestal and made everyone aware of the real potential of SSB.

Since there were only 1600 KWS-1 built, and many were destroyed by the military, it is a real pleasure to own a nice set of the Gold Dust Twins.