These cold days are made a little more pleasant now with the warm glow of tubes in the shack. This radio was given to me as part of an estate purchase. It’s been years since I worked with tubes, so I decided to try getting it to work. It took quite a bit of cleaning – all the tubes were removed and shined up, the pots were cleaned, and layers of dust were blown out. The circuits looked in good shape, so I checked for common failures. Nothing major was found, but plenty of minor items needed attention.
I haven’t had a tube tester since the mid 1980′s, so I had to have a little faith that the valves were still performing as intended. The transmit relay was pretty burned, so I swapped it with the VOX relay. Several other small parts were changed, and the power supply was looked over. The power cord didn’t look too good so I installed a new one, and touched up some of the solder joints.
When I applied power, things lit up, and before long I had audio. But I didn’t have transmit. The tone oscillator was intermittent, which turned out to be a misadjusted transistor bias control. I had to connect the scope and fix the balanced modulator since too much carrier was present. Several small and time consuming problems later, and I was able to tune up full rated power.
Finally, I connected the antenna and tuned her up. The receive audio was very nice and full. Drift wasn’t too bad after it warmed up. And my signal reports were great considering the antenna I’m using. It is particularly good on 80 and 40 meters. I missed the adjustable IF width and shift from my FT-757 when dealing with noisy conditions (making 20 meters a challenge), but it was easy to listen to, without listener fatigue. Signals were moving the S-meter to levels I don’t see on the FT-757, with low internal noise.
I’m thrilled to have a functioning vintage tube radio in the shack, and pleased to have been able to service it without curling my hair. My next challenge is a Swan 250C for 6 meters, with the 2 meter transverter. It needs a little more work, and I want to add FM capability.