11-30-2011, 09:35 PM
terry, you make me look stupid!! please take that as a compliment.
Tonight I dug into the tube voltages on the sub chassis and found o voltage at the plate of the 6a8 mixer and the 6k7 rf tube. I traced the lack of voltage to resistor #47 a 1000ohm that was open. I replaced it and now I have voltage to those tubes, that fixed the higher b+ voltage readings, now I'm about 10 to 15 volts less on the plates. Unfortunately that killed all my static now I 'm back to the low humm. I disconnected the wire from the 1meg ohm resistor to the #111 resisitor (tube top wire circuit 6r7) for now because it did not do anything but raise the plate voltage from 46 to 89 volts.
Now the voltage reading at resistors 115 &116 (134&135) is -15.4 instead of -25.4. I s that better or too low?
I still have feedback when touching the 6r7 top.
Is my next step to trace the plate wire of the 6r7 and try to find out why I'm 25volts low? There was a ground wire running to pin 3(plate) and I moved it to pin 8, did I look at the schematic correctly or should I move back to pin 3?
If I tack on a phono jack off the center tap of the volume control and it works, does that tell me my 6r7 circuit is working properly?
Bob
Tonight I dug into the tube voltages on the sub chassis and found o voltage at the plate of the 6a8 mixer and the 6k7 rf tube. I traced the lack of voltage to resistor #47 a 1000ohm that was open. I replaced it and now I have voltage to those tubes, that fixed the higher b+ voltage readings, now I'm about 10 to 15 volts less on the plates. Unfortunately that killed all my static now I 'm back to the low humm. I disconnected the wire from the 1meg ohm resistor to the #111 resisitor (tube top wire circuit 6r7) for now because it did not do anything but raise the plate voltage from 46 to 89 volts.
Now the voltage reading at resistors 115 &116 (134&135) is -15.4 instead of -25.4. I s that better or too low?
I still have feedback when touching the 6r7 top.
Is my next step to trace the plate wire of the 6r7 and try to find out why I'm 25volts low? There was a ground wire running to pin 3(plate) and I moved it to pin 8, did I look at the schematic correctly or should I move back to pin 3?
If I tack on a phono jack off the center tap of the volume control and it works, does that tell me my 6r7 circuit is working properly?
Bob
