Tube Amp Archive

Resurrecting this thread because I really need help getting the schematic for the 500a. I picked up a nice one and would like to get it back into working condition.

100k resistor at cathode follower (pin 8 ) was reading 100k but when I finally got in there and messed with it, it shows an open. I replaced that resistor and buttoned everything up. Works like a charm now. I guess with voltage applied, it was opening and when I removed it would still show correct r...

Roe wrote: ↑Wed Sep 11, 2024 7:43 am

TNTim wrote: ↑Wed Sep 11, 2024 2:55 am So I think the issue is in the second gain stage and cathode follower. I have almost no voltage on both cathodes and over 400V across the 100k resistor attached to the plate.

try a new tube in v2

I tried that with 2 different good tubes.

So I think the issue is in the second gain stage and cathode follower. I have almost no voltage on both cathodes and over 400V across the 100k resistor attached to the plate.

Both output tubes can not be idling properly if you have that high of a plate voltage showing up. As posted check to see if the 470 ohm screen resistor on either tubes pin 4 is open. Yeah I agree. According to the schematic, at TP7 (Plate voltage for 6L6) it should be 257. It reads 487. 486V at gri...

I've got a 2000 era Bassman '59 reissue. New filter caps. High voltages look good. It's got a horrible distorted "fuzz" sound and low output. If you turn off the power, as the voltage goes down, the natural sound of the amp comes alive and then fades out with the power dissipating. I have about 487V...

Thanks!!

The intensity pot is crudely soldered to a small printed circuit board. One leg of that pot had a bad joint that only showed up when you tightened down the pot to the front of the chassis. I fixed that and that corrected the issue. I appreciate your help.

I tested the 4M intensity pot/switch Measures correctly throughout the range. The switch portion works as it turns on/off the "after beat". No bad solder joints.

I have a late 60's Ampgeg Gemini I G12. This one has the printed circuit board. The Tremolo works great...maybe too great. The intensity pot does nothing to turn down the intensity. I checked the functionality of the 4M pot and it is fine. The after beat works great too. What could cause it to stay ...