- 2025
- Nov
- 24
An Unknown 2-dial TRF radio part 3: Things inside identified.
When last we met, I had identified where the tubes went, so now it’s time to figure out where the power supplies need to connect. This looked very complex at first, but once I started reading about this type of radio, it became obvious how things were supposed to connect. But first, some other things to take care of.
There are a number of broken connections here. The original builder used some very precise bent wires in spots, and made “meh it has to connect” connections in others. Some of those have broken because they were just laid on their connection point without any kind of mechanical connection, and hit with a blob of solder. There’s even some solder blobs in the case indicating repairs were made in situ at times.
The first is the RF amp. This one was just laid on it’s terminal and soldered.
This one was resting against it’s connection point and poorly soldered.
And the final one is just a wire that pulled out of a poorly crimped fork. This one is the 90V supply feed for the final AF amp, and uses the headphones as it’s bias.
With that out of the way, it’s time to move on to identifying the battery connections. I’ve already identified the tube layout, so it was mostly a matter of tracing back to see where the plate of each tube went. It threw me for a minute that the detector and final AF amps both connection via one of the interstage transformers, but that’s how these were built.
I found it interesting that the unit has two 90V connections, but then it occured to me that the builder was trying to keep RF out of the AF to prevent squealing. If you’ve ever had a radio with a bad AGC capacitor, you know what I mean…
Before applying power, there’s going to need to be some substantial cleanup. All connections are oxidized to the point of insulation - the power switch, for example, doesn’t even read resistance when closed. The tuning gangs are locked up tight, and the battery cables are no longer conductors.
The next step is to check coils and transformers to make sure all are giving a useful reading. Stay tuned!
Next part of this series: https://wereboar.com … io-part-4-full-stop/
Previous part of this series: https://wereboar.com … fying-things-inside/