Collins KWM-2 Vintage Ham Radio Transceiver

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The Collins Radio Company sought to design and manufacture the best they could in every aspect and all their equipment was of a very high quality.

The Collins KWM2 was the ultimate example of their engineering philosophy and RF circuit design. It was seen as the market leader of the time which can hold its own even today even though it is now a vintage radio.

The Collins KWM2 was an HF amateur bands only transceiver which was able to develop 100 watts PEP output on single sideband. Offering ease of operation along with a high performance specification it offered the ultimate for anyone who could afford it.

The KWM-2 had a distinctive style with its rounded edges and leather effect on the front panel. Even today, this radio would not look out of place in a modern ham radio shack.

Collins KWM2 specifications

The Collins KWM-2 provided a very good specification and operated well as a result. The RF circuit design utilised many aspects like balanced mixers and other high performance circuits to achieve this performance. In many respects it was well ahead of its time and now leads the field when compared to many other vintage radios of its time.

    * Although the KWM2 was the basic transceiver used, the KWM2A was a later development used by the US MARS or Military Affiliate Radio Service and other military organisations. It had an additional crystal board which enabled the Collins KWM2A to use an additional 14 crystals to cover frequencies outside the amateur radio bands. A front panel indicator was provided to show which band was in use.

    ** Only one crystal was provided for the 10 metre band as the whole band extends from 28.0 to 29.7 Mc/s and this allowed the owner to select the required crystals for the frequency range they required.

Collins KWM-2 basics

The Collins KWM-2 was introduced in 1959 as a successor to the KWM-1. The radio was most successful ever produced by Collins and was produced for over 25 years, being used by the amateur radio fraternity around the globe. It also appears that well over 25 000 of these sets were manufactured during its long production life. It certainly had many industry leading aspects to its RF circuit design.

A version of the transceiver known as the KWM-2A was produced for MARS - military affiliate radio system use as well as for other military applications. This radio provided the same amateur radio band coverage as the KWM-2, but also gave access to other frequencies as well. It was widely used by MARS stations in Vietnam and other locations to give phone patch connections for the US troops back to home.

In terms of its performance, the KWM-2 provided remarkable stability for its day. It had a dial that was able to provide the frequency (accurately) down to 1kc/s and the drift was also minimal at better than 100 c/s per hour. These were remarkable figures for the day and gave the KWM-2 a good lead over the opposition and set the standard for others to follow.

The KWM-2 used an external power supply. Two were available from Collins. The PM-2 was the lower cost version and had only a limited duty cycle which limited the operation of the radio, but was suitable for much intermittent operation. For more intense use and greater flexibility the 516F was recommended as it enabled the fully operational specification to be realised.

Collins KWM-2 valves / tubes

The KWM-2 circuit design used a total of 18 vacuum tubes or valves. Most of them were small B7G or B9A types but the two output tubes were much larger in view of the power handling capability required.

The line-up within the RF circuit design incorporated the following devices: 6AZ8, 6U8A, 6AZ8, 6AZ8, 12AT7, 12AT7, 6DC6, 7543, 6CL6, 6146A, 6146A, 6U8A, 6U8A, 6U8A, 6BN8, 6BN8, 6EB8, 6BN8.

Note "A" and "B" in the "Use within circuit" column refer to the sections of the tubes / valves where a device has more than one section to it.

In addition to the tubes / valves used within the KWM-2, a number of semiconductor diodes were also used and these undertook a variety of functions within the overall KWM-2 circuit.

In 1959 when the KWM-2 was launched, semiconductor technology was reaching the state where some devices could be used in high performance RF circuit designs.

KWM-2 basic circuit description

The KWM-2 is an SSB and CW (no AM or FM) transceiver that operates between 3.4 and 30Mc/s. The receiver circuit uses a double conversion topology with a crystal controlled high frequency conversion (first conversion for the receiver) and a VFO controlled LF conversion.

The HF IF covers 200 kc/s between 2.955 and 3.155 Mc/s giving a flat response over 200 kc/s.

The low frequency IF is at the standard frequency of 455 kc/s.

In many respects, the the KWM-2 was a development that combined the Collins 75S-1 vintage radio receiver with the companion 32S-1 transmitter. However it used a technique called sidetone generation for CW which many thought was something of a compromise. Some modifications to provide carrier generated CW have appeared in the publications as the sidetone generation is not considered to be optimum for a variety of reasons.

In the design many circuits are common to the receiver and transmitter. The transmitter and receiver use common oscillators as well as a common mechanical filter and a common RF amplifier (but not the power amplifier). This reduces the number of circuits required and enables the power consumption as well as the size to be reduced.

As the KWM-2 was designed for mobile use as well as fixed station operation, size and power consumption were important aspects of the design.

The Collins KWM-2 rightly had an enviable reputation for performance and quality. Collins Radio aimed high in terms of overall performance and quality. With these radios still sought after today, it is clear that Collins succeeded with their KWM-2 making it a true classic vintage radio from the late 1950s which is still able to perform well today.

  Written by Ian Poole .
  Experienced electronics engineer and author.

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