The Amp Garage

Hello Franco,
Can you describe the amp you wish to set the trimmer on? What kind of power tubes does it have? How many? Do they have 1 ohm resistors installed on the cathode?

What test equipment do you have available?

Been doing some work with this amp today. A while back I robbed the PT from it to replace the one in my SSS. I just received and installed the replacement from Amp Parts Direct. A Heyboer for a Fender 100Watt, but with 320-0-320 vs the 340-0-340 Heyboer from Mojotone that I removed. New voltages: 10...

martin manning wrote: ↑Sun May 26, 2024 4:33 pm

GAStan wrote: ↑Sat May 25, 2024 2:35 amThe bleeder is definitely a good idea.

I made a small tweak to the eyelet board .pdf on this. Increased the current limiter to 47R, and decreased the bleeder to 150k. Should have it drained in a minute or so.

Thanks for the heads up, I'll check it out.

Hope that solves it! The speaker output should be in phase with the PI input. Yours will be the first with the new resistors added to the bipolar supply. I’ll be interested to hear how that works in hardware. It did fix the problem, thanks. The bleeder is definitely a good idea. The +170 volt caps ...

Found a problem. Hopefully the problem. Circled 270k should be 270r. Voltages on V6 are much higher than on Viperdoc's schematic. Will work on this more tomorrow.

I've been working on an oscillation. It's only in the power section, from the PI to speakers. Goes away if feedback from speaker is disconnected. First three of the below are Channel 1: 8 ohm dummy load; Channel 2: PI (V6) Pin 6. 400 hz signal. 8 ohm dummy load. Refer to Viperdoc's schematic . Pic 1...

Completed installation of bipolar power supply. Amp is now working again with better B+ and other voltages. Question: with the decreased voltage the bipolar supply provides V7 does this limit the clean headroom? Volume? Is there a noticeable tonal difference between the original and bipolar supplie...

Completed installation of bipolar power supply. Amp is now working again with better B+ and other voltages. When plugging in 8 ohm dummy load had a déjà vu moment. I used Puretone jacks on the unswitched outputs because they have better contacts than Switchcraft. However they are a little harder to ...

Sockets are how i see new.. and Belton, so means high quality.. Never failed any in my life. So there is only 0.1% of chance that sockets are a problem.. Probably output tubes.. Yes brand new Belton sockets. I found nothing wrong, no signs of tracking and no residual carbon from the resistors that ...

This is bad tube problem.. pls measure resistance directly on the tube pins, between 2-3. Using a Fluke 87 DMM, one tube has no continuity on any pin to any other pin (open heater). The other three only have continuity from pins 2 to 7 (heaters), no other pins have continuity to any other pins. I'm...

Once you have an arc occur there may be carbon tracking on the tube sockets which must be completely removed to prevent more arcing. If the socket material has been burned, replacing the socket may be necessary. So what caused the initial arcing? I think it was most likely an oscillation in the pow...

Spent the morning putting a PT from Mojotone in. Now the B+ is 458vdc in standby. Put it to Operate and saw a MAJOR arc in V8 and inside the amp at the same time. V8 heater opened and evidently shorted to B+. Cut the power immediately. Both 100 ohm heater to ground resistors smoked. Replaced 100 ohm...

Hi Glenn Apologies if this is me being stupid. Given that the #102 is providing 428V with a 340-0-340 @400mA PT isn't it reasonable you'd get the lower B+ reading of 414V from the 320-0-320 @450mA PT in the SSS with the same wall voltage? Could it be the higher 440V reading you noted was taken unde...

I had the same problem in one amp, when inside the box.. chassis and power transformer were extremelly hot.. while outside on the table, chassis and PT temp was just moderate, nothing to worry about... Then i discover that there is no sufficient air circulation in the cabinet, and tubes were heatin...

102 amp is still on, Operate, idle-no input. Transformer is very warm, I can only keep my fingers on it for 2-3 seconds. Similar in temperature to SSS transformer. This is after nearly 4 hours operation.