This radio came to the shop all the way from California. It had visited several shops for a irritating hum and buzz on both receive and transmit functions. This radio shares a 6L6 as both audio amp and modulator, so I new to look in that area first. This is the early model that was mostly hard wired with a few plug in boards. I guess you could call it a Hybrid. I found several components that were incorrect, plus some added capacitors that were an attempt to dampen the noise. I remove all of that and returned those circuits to stock. Still the buzz remained. Then I discovered a very sensitive area, if I simply applied pressure, the buzz would subside. Turned out that the cause was weak grounds around the 6GH8 tubes (preamp).I ended up directly soldering their bases to the chassis and added slip on shields to each tube. Problem solved. Im sure this was stress/wear over time, the pop riveted based loosened or slight corrosion set in. Interesting project, thought it would be a great tech tip.
6 окт 2024
