Peavey VK 100 Low Power

[Felton Pruett]

Hi. I have a Peavey Valveking100 head I bought used for peanuts to learn about tube amps. When I first got it it was only putting out about 60 watts. I've done several mods, removed the A/AB switch, changed a few caps and resistors here and there, re-tubed it and put in a new OT transformer. It sounds great and everything works but still no more than 23 VAC at the output should be around 30. Test tone in the preamp or the effects return same thing. 450VDC at the output plates. Any Ideas?

[The Dude]

We don't know what your load impedance is, so it's hard to tell if that output voltage is actually low or not. (P= V squared/R)

Can you tell us what your speaker or dummy load setup is? How many speakers, what impedance, series or parallel, etc.

[Felton Pruett]

I use a 8 ohm 100 watt resistor dummy load and a 1000 hz test tone off YouTube at 0 db at the mixer with everything at 12:00 through the clean channel. Turned up into distortion territory about 2:00 is where the max voltage is. Dimed it actually goes down to about 16 volts. The same set up with a Vox NT50H with two EL34s gets me 19 to 20 volts, dimes about 23. Am I measuring it wrong? I would think the Peavey with 4 6L6s would outperform the 50 watt Vox but they are real similar volume and headroom-wise.

[The Dude]

You say you changed the output transformer. Did you replace with an original part or something different. If different, what did you use. Might be a problem with transformer impedance.

You say, "Turned up into distortion territory about 2:00 is where the max voltage is. Dimed it actually goes down to about 16 volts." This makes me think you might have a problem with the NFB circuit "kicking back" too much.

[Felton Pruett]

I put in a Weber WOT100LHR OT which was an improvement sound wise but not much in watts. I'm going to play with some resistor values in the NFB and see what that does. I'm still learning but I thought it odd that the power would go down from 2:00 to full on. I thought it had something to do with the way the signal was clipping or something.