I got this set of radios from Charl ZS1ZZ sometime near the end of 2024. They are all-vacuum tube radios from the 1960’s. They both somewhat worked when I plugged them into my current limiter, but not fully. The receiver (FRDX400) only received on some bands, and not very well on the ones that it did work on. The transmitter (FLDX400) didn’t work on any band but did turn on. I first gave both radios a thorough clean and sanded the rust off of the panels. I checked all the valves in both radio and they all looked fine. All of the valve filaments turned on in both radios. I then sprayed contact cleaner into all of the potentiometers and switched I could find on the radio. After cleaning the receiver all of the bands sprung back to life, but it still didn’t work very well. It wasn’t as sensitive as it was spec ’ed to be. I ran through the alignment procedure from the service manual and re-aligned the rf and if sections. It then worked perfectly on all bands and had a sensitivity of 0.5uV.
I then had a look at the transmitter. I pulled out the finals and checked them for shorts. They were fine. I then measured the plate voltage on the finals and that was also good. Since the voltages on the finals looked OK, I started signal tracing the rig. I lost the signal after the 1st mixer. It took me ages to work out that the mixer balance potentiometer wasn’t making good contact. I had missed it with the contact cleaner earlier on when I was cleaning. I sprayed contact cleaner into and re-balanced the mixer and it started transmitting. I also performed a full alignment on the transmitter, and it works perfectly now.
I plan for these radios to be paired with my linear amplifier when its all set up, or my fl-101 and fr-101 set (or possibly my ft901d), I am not quite sure yet.
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