[Joeztech]

Today I finally solved the problem with the radio being very slow to produce audio and being very distorted at first when it did. I started by checking the audio at the detector diodes of the 7C6 using my oscilloscope. I had good audio there. I moved on to the grid of the 7C6 and had good audio there. There was also good audio at the plate of the 7C6 1st. audio tube - this all was done from a cold start. Yet the audio output would not come on for nearly two full minutes. I kept going with the scope moved further along the signal path, turning the set off until a cold start could be initiated again. Finally I reached pin 5 of the 6J5 Phase Inverter tube. When I placed the scope probe on the end of the .01 coupling capacitor to pin 5 I saw the lead move physically on the socket pin. I had forgotten to solder that end of the coupling capacitor when I had replaced it probably over a month ago! I suspect that what happened was that I interrupted my work and continued on later and just did not spot the loose connection until today.

The 265 ohm candohm resistor seems to work just fine now with adequate audio output, so it will stay in the set. It is working with two new 6V6GT output tubes in place of the OEM 6K6GT tubes, so things look normal from the standpoint of audio output level and distortion seems minimal. Jcassity mentioned that his set had a somewhat higher candohm negative bias resistor in it and worked well. At first I wondered if this set needed a 150 ohm resistor after changing to 6V6GT tubes, but that turned out not to be true.

There is no substitute for good troubleshooting techniques and a step by step procedure to follow. Proving good audio from the detector on was the key to establishing where the problem was happening.

Now I will be able to wrap this set up soon and present it to the owners.

Joe