Working on a Peavey Windsor Studio that is a customer's. The complaint was the amplifier got weaker and has no headroom. After checking it I was only getting about 3-4 watts into 8 ohms with a good amount of negative clip at that. it had an EL34 in it I replaced and basically had the same results. I had also put a 6550 and only noticed a 1 watt improvement.
Here are the no signal DC voltages I am getting:
Plate: 450 Vdc, screen: 406 Vdc, cathode: 29 Vdc.
at ~ 8Watts out into 8 ohms:
Plate:450 Vdc, screen: 398 Vdc, Cathode 31 Vdc.
Of course this is about 25 - 30% THD and heavy negative clipping.
Couple of other things the 12AX7 driver tube seems fine and has plenty of headroom left when the output is distorting. I have replaced the OT with a new unit with the same results. Cathode resistor (400 ohms) and the bypass capacitor measure fine. Also I have checked and completely bypassed the output attenuator with no improvement. Nothing looks burnt or discolored..... no signs of arcing.
Anyone out there familiar with these single ended amp's? I cant get any info from tech support at Peavey they claim they have the same schematic I have which gives no information on the power amp section, no DC voltages or output spec's.
On the back of the amp it is marked "17.9 VRMS" and "20 Watts" next to the Impedance selector. I find this a stretch for a single ended amp, and at what conditions?
Any info would be greatly appreciated, Thanks!
Brad
Windsor Studio weak output
Moderators: pompeiisneaks, Colossal