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previous: SteveG Ray,Thanks for the ... -- 7/9/2000 2:17 AM

Re: Peavey Deuce Amp Tube Theory Question

7/9/2000 1:23 PM
Ray Ivers	Re: Peavey Deuce Amp Tube Theory Question Steve S., Mitch's post (thanks, Mitch!) to me says it all. The Peavey's a cathode-drive circuit, probably using close-to-Class-B biasing conditions and reduced screen voltage, looking for more power, extended tube life, and reliability. I personally like this design for a master-volume amp's power amp, PROVIDED that the preamp sounds good; if this Peavey has the multi-colored knobs, I know I probably wouldn't like the preamp's sound, but that's me. If you're going to overdrive the power amp, Mitch's suggestion of a different driver stage design, perhaps a long-tail driver, will give you much more of a conventional power-amp overdrive sound. Remember, you're also going to have to build a bias supply; if I'm not mistaken, right now there probably a positive voltage of between 20 and 30 volts on the output tube grids. In fact, you will basically have to completely redesign the entire power amp, from the phase inverter on out. I think I would leave the screen supply/voltage as is, although you could go hog-wild and install a choke and cap in the B+ line and tap off the screens from the 'downstream' side of the choke, using 470 or 1K ohm screen resistors. Steve G., The power supply series dropping resistor between the OT center-tap B+ and the screen's connection IS, in effect, the (shared) screen resistor, so your amp does have current limiting for the screens. This should work just fine - no additional screen resistances are needed. I imagine the series dropping resistance is probably 1K ohm or less. Ray

7/9/2000 1:23 PM

Ray Ivers

Re: Peavey Deuce Amp Tube Theory Question

Steve S.,

Mitch's post (thanks, Mitch!) to me says it all. The Peavey's a cathode-drive circuit, probably using close-to-Class-B biasing conditions and reduced screen voltage, looking for more power, extended tube life, and reliability. I personally like this design for a master-volume amp's power amp, PROVIDED that the preamp sounds good; if this Peavey has the multi-colored knobs, I know I probably wouldn't like the preamp's sound, but that's me. If you're going to overdrive the power amp, Mitch's suggestion of a different driver stage design, perhaps a long-tail driver, will give you much more of a conventional power-amp overdrive sound. Remember, you're also going to have to build a bias supply; if I'm not mistaken, right now there probably a positive voltage of between 20 and 30 volts on the output tube grids. In fact, you will basically have to completely redesign the entire power amp, from the phase inverter on out. I think I would leave the screen supply/voltage as is, although you could go hog-wild and install a choke and cap in the B+ line and tap off the screens from the 'downstream' side of the choke, using 470 or 1K ohm screen resistors.

Steve G.,

The power supply series dropping resistor between the OT center-tap B+ and the screen's connection IS, in effect, the (shared) screen resistor, so your amp does have current limiting for the screens. This should work just fine - no additional screen resistances are needed. I imagine the series dropping resistance is probably 1K ohm or less.

Ray