DL6HA SSB Transceiver

Posted on January 29, 2024

A couple of years ago I was asked to have a look at an old 2m SSB Transceiver that Ross G6GVI had inherited from another amateur. It was in need of restoration and re-alignment. The transceiver was originally built in 1971 from a construction project in VHF Communications Magazine. it took me a while to get the time to get it on the bench and have a look at this transceiver, but have recently completed it. It is very well built and uses all discrete components of silicon transistors and FETs. The module boards were all built as kits taken from the original project.

When I tested the transceiver, it worked fine on receive and seemed quite sensitive. On transmit it gave about 4w output. I arranged a sked with Ross G6GVI so that we could see how the transceiver sounded. The audio seemed very muffled and flat, also the pre-selector was not peaking at the same time as the receiver. The AGC didn’t seem to working on receive, but the S Meter is working fine. Time to do a bit of fault finding…

Changing the microphone didn’t make much difference to the audio, but after looking at the circuit and audio board I spotted a 100n capacitor had been added across the mic input. This was removed and the audio sounded much better. The pre-selector tunes the RF stages on transmit and receive by using varicap diodes in each stage. I noticed that the tuning slugs on the coils were very loose and had obviously moved over time. I re-aligned the RF stages and brought the pre-selector back into sync again. Next is the AGC problem. The AGC works in conjunction with the RF Gain, a preset had been added in series with the AGC Control Voltage. Adjusting this caused the AGC to start working again, but it needs quite a strong signal for the AGC to kick in properly. This seems to be because of the characteristics of the old silicon transistors in the RF stages that the AGC controls. I decided to set the levels as near as possible and leave it as it is now quite acceptable. Finally, I peaked up the PA tuning capacitors to give a nice 9w output on 2m into my antenna.

Now that the transceiver is working fine, I now concentrated on the cosmetic part of renovation. The case had never been painted and finished off and was just plain scratched aluminium. The front panel was painted black, but looked very sad with it’s stick on lettering. I decided to paint the case grey and found a very nice textured light grey colour. The front panel was painted with black Hammerite spray. New lettering was added printed on decal paper. A set of new knobs finished off the project.