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Thank you guys. The story goes on: I have disassembled and cleaned Ultra Hi and Midrange switches, cleaned contacts and now I see how...

Okay, so here are idle DC voltages for the preamp tubes and filter caps. Grid voltages were too small to measure accurately. I noticed...

Yeah, had a 70s Twin Reverb come in with dead power tubes; after replacing filter and bias caps, still had ridiculous amount of hum. It...

https://reverb.com/item/29196508-schematic-diagram-package-for-jmi-era-vox-ac-30-4-and-ac30-6-amps-1960-through-1967 Read more... OS/056...

I think it would be considered a "grid leak resistor as it appears directly after the coupling cap, and is tied to ground. However... ...

No doubt, I just forgot to draw the coupling cap. So I did a little more work. According to the info provided by the datasheet, the...

Hey, Rajan. Got anything to contribute?

You asked ;)

It would be fun to have the audio of that ;)

Considering all the weird problems I've encountered with these due to intermittent preamp PC board connections, I think that might be the...

I did something this week while re-capping a AA165 Pro Reverb. While pulling the old 20uF filter caps at the same time, which I don't...

Some 12AX7 have a higher than desirable degree of (usually positive) grid current, an operating point with very low plate voltage seems to...

I've seen bad cathode caps do weird stuff like that. Can't hurt to try.

I don't advise shorting out Q4 & Q5, since you need their Vce drops to power Q2/Q2A. The 555 timer IC generates the delay-turn-on, which...

I think I may need some clarity. 270k would be very high for a "grid resistor" but very typical for a "grid leak resistor". And "grid...

https://www.youtube.com/watch?v=oQud4emaSek Vox Pop - The Story of Dick Denney and the AC30 amp ...

I don't advise shorting out Q4 & Q5, since you need their Vce drops to power Q2/Q2A. The 555 timer IC generates the delay-turn-on, which...

You may be onto it as well Helmholtz. I am running a "20W" OT, but I would think based on the sturdy power transformer, and the high plate...

Thanks Chuck, I will play with the values of the 6L6 tubes as you mentioned, I just may not use 150k owning to the fact of the .047uf caps...

Strange. Have you also tried different tubes in V2? Does the instrument connected have active electronics? Just excluding the DCV comes...

DC is positive WRT ground, and yes, vanishes when no plug inserted (input jack is properly grounding the tip).

I'm glad as well..The customer picked it up earlier this afternoon......and he was quite happy..... Cheers

I would think of OT core saturation caused by PI signal asymmetry (means net DC in the primary) and low frequency content. Only a...

I think the swirly distortion must be crossover distortion resulting from the bias voltage increase at the cathode resistor with conduction...

Correct, I missed this path. It was just a general remark. As shown without coupling caps the grid will see (high) positive voltage.

Well, still can't explain the stray DC on the input, but my main issue, nasty hum, was coming from a bad solder joint on the Lead channel's...

There's a DC ground reference through the feedback resistor and output load resistor.

Is the DC positive or negative wrt ground? I guess the voltage drops to zero without a plug inserted?

Not much known about "secondary emission" in small signal triodes. What's your source of information?

secondary emission is a byproduct of fairly low anode voltage ,especially on modern production tubes,if its annoying try add a 100n and...

Yesterday exactly the same thing happened to me with a DC3. The volume of the guitar creaked a lot with the lead channel selected. I took...

That resistor is part of a short feedback loop. Probably to stabilize the circuit? Such loops appear elsewhere in the amp too I notice. Not...

At least if you still have noise with the output stage out of the circuit. it will be narrow the search down. You could short out Q4 and Q5...