Power xfrmer wire color? Help!

[ManRay]

I am reassembling a peavy valvking 100W head but cannot find the wire color codes for the power transformer. I have a schematic, but it gives me nothing. I have emailed customer support at Peavey and they have politely said nothing in return for about a week. I have a multimeter and can perform volage tests, but I have no clue where to begin. If anyone could give me a hand I would appreciate it.

Thanks,
MR.

[Jazz P Bass]

Peavey ValveKing

Can you post the schematic?

[Enzo]

Sure, no wire colors. One really should mark the wires before disconnecting them.

You have three secondaries - high voltage, bias, and low voltage. APply power to the primary and measure AC voltages at the groups of wires.


The entire Peavey company was on vacation the week of Thanksgiving

[ManRay]

Happy Turkey Day Peavey

Ok,

All 8 of the wires are coming out of the same side of the transformer, but I have duplicates of every wire color except Black and Blue. I am supposing that these are the primaries. How am I to determine which is Hot and which is Neutral? And once I have established this, do I just measure the AC Volts coming from one wire to another of the same color or measure from the wire to ground?

Thanks,
MR.

[Enzo]

It is a power transformer, not a signal transformer, so the absolute phase of the voltage is not important. I would choose black for hot, blue for neutral myself, but it shouldn;t matter.

You would power the primary - I would connect it through the amp circuit so you have teh fuse and power switch in place. Then measure the secondary voltages. With the wires disconnected there is no ground, so you can't take meaningful measurements to ground. measure wire to wire.

I'd expect something in the area of maybe 300VAC, maybe 40VAC and maybe 20VAC. SHould be easy to determine which is the high voltage, and the low voltage winding serves the heaters, so it will probably have the heaviest wire.

[ManRay]

I got ~350VAC, ~80VAC, and ~25VAC. So I have plugged these wires into the High Volt, Bias, and Low Volt respectively, but I get no sound out of the amp. I have heater glow when I power the amp up and the tubes glow blue when I switch off standby but no sound. I have tried plugging into the effects loop return and I get some noise when I touch the tip of the cable but that is the extent of it. That leads me to believe that the power section works, and my problem is in the preamp. Any clues? I really appreciate all of the help so far Enzo.

Thanks,
MR.

[Enzo]

Plug your guitar into the FX return, get sound from the speaker? it won't be loud, but maybe practice volume.

I guess my voltage estimates were close on a couple of them anyway.


Send the FX send signal to some other amp and speaker. Is ther signal happening? If so, they try plugging a cord from FX send to FX return.

If the preamp out if silent, then I have to ask, why was the amp disassembled in the first place? it is all tube in there, so if the preamp doesn;t pass signal, I go down the row of tubes verifying plate voltage and enough on the cathodes to verify tube conduction.

If all those are present, then apply a signal to the input, and trace it stage by stage through the amp until you find a point it disappears.

[ManRay]

I do get practice volume when I'm in the effects return, and I get barely noticeable sound from the regular input when I'm cranked. I ran from the send to a working amp and got no volume.

Enzo, you mentioned measuring plate voltages across preamp tubes until it stops. How can I measure for plate voltages and cathode conduction with meter?

Thanks,

[ManRay]

Plate voltages are not steady?

Ok, I measured my plate voltages on my preamp tubes by running the meter from plate to chasis ground. I got about 150 volts DC, but the meter never settled anywhere. Is this normal? I got voltage from all 4 plates from the first 2 tubes, and I didn't measure from the 3rd because I think that it is the phase inverter and comes after the FX return. I am not exactly sure what I am looking for at this point. I swam out of my depth on this one long ago.

I appreciate all the help thus far Enzo. I am a hell of a lot closer to getting this one back. If anyone else has any thoughts or guidance, then I am open to suggestion.

Thanks,
MR.

[52 Bill]

Follow Enzo's advice.

You need to check the voltages on the plates and on the cathodes to see if the tube is conducting.

On a 12AX7 the plates are pins 1 and 6 cathodes are 3 and 8. If you have voltage on pin 1 but no voltage on pin 3, the tube is not turning on. Same thing for pin 6 and pin 8.

Look for maybe 1-2 Vdc on each cathode in the preamp stages.

If the voltages are ok, then plug a signal into the front of the amp and trace it through stage by stage until it stops, and there is your problem area.

[Enzo]

I'd say if you get 150v more or less on each plate then the tube is conducting. If the tube stops, then the plate voltage will rise to the B+ voltage. Ohm's Law - no current, no voltage drop.

Your preamp is obviousl;y not working right. SO what Bill said is next. APply a steady strong signal to the amp input and follow it through the stages. A scope is ideal, but we are dealing with sound being either present or missing, so you can use your meter set to AC volts to follow the signal. You can connect a CD player or something to the input to keep your hands free. Or a keyboard. Stick a book of matches between keys to wedge one down for a steady tone.

[ManRay]

Footswitch magic

UPDATE:

I measured the plates and cathodes and got measurements close to what you guys suggested. Then on a whim I plugged in the footswitch and got full on volume from this sucker. It appears that toggling the first button brings my amp back down to miniscule volume again and the second button switches channel like normal...Any thoughts? I suppose that I can live with this quirk, but I would prefer to get the amp running normally.

Thanks again for all of the help!!!

[Jazz P Bass]

Peavey Gain Boost

Your footswitch is selecting either gain boost or normal signal.
This may be a hint.