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Post subject: Re: 80-81 Deluxe Reverb: Silverface with black faceplate.
Posted: Fri Sep 06, 2013 8:49 pm
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Location: Tombstone Territory
BMW2002Ti wrote:
" 2000 pico-farad grid-to-ground stubbers on the 6V6GT. "

OEM should be 1200 pico-farads. In any event. I'd keep them in the circuit. Change the grid load on the phase inverter to 1meg-ohm resistors. See how the amp sounds like. You will need a good 12AT7 is this position with the 1-meg ohm resistors. I'd opt for a nice NOS Sylvania 12AT7WA. Have it check for balance across the triode sections. And low-noise.

If it sounds ok.. unsolder one end of the pico-farad resistors on the 6V6GTs. See if the bias becomes unsteady. If not... try the amp out. Any change in tone? If not.. solder the the caps back in place. They are there to help stop high-frequency induced instabilites. Which may cause problems with the 6V6GTs.

If the tone does change, for the better, without the caps. Try the amp out for awhile and see if the 6V6GTs seem ok. No red plating or overheating. If all is ok. leave the caps out. If you are using good 6V6GT (like RCA, GE, or Sylvania) --- you'll prolly be ok. As this is what most ppl used in this amp, back in the AB763 days. If you are using some modern Chinese or Russian made 6V6GT, the lack of pico-farad caps MAY reduce life of the tubes.


+1

I went through this drill with a client's '75 Deluxe Reverb a few years back and tried various scenarios involving those grid-snubbers on the power tubes. Ultimately I left everything in situ and merely selected a carefully-vetted set of glass and a nice speaker to keep everything on the chassis within spec. Which is why I left my '78 DR all stock (no sense in paying for the same real estate twice).

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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