Universal Guitar Amp with Vibrator and Reverberator

[tigerzilly]

Are you sure? I've not seen resistors or pots lower in value.

Yes Im sure. I measured multiple times. The pot says 100k but measures 10k. I was thinking perhaps the pot was improperly assembled when manufactured.

[tigerzilly]

Were you able to check how close your speaker line is to 0Vdc - that will be a simple indicator that your output stage is biasing up ok.

Was a signal on your scope looking fairly clean for mid-tone controls, and could you up the volume (perhaps with a resistor load instead of speaker) to show symmetric clipping?

Well I replaced four pots and re-powered. I was getting .18 volts at the speaker output. Sinewave looked good, but spiked with max treble....

...then my speaker output wires shorted. I smelled burning near the reverb pot. Now I have 29 volts dc at output and no sinewave. Ugh!

[tigerzilly]

Now I can believe itīs actually 10k, you measured 10k, and maybe you misread it as 100k.

Suggest you do not pull parts ar random, and even less having no schematic.

An accident waiting bto happen.

Absolute worst case, leave it aside for now.

Better unrepaired but original than *destroyed*.

It definitely reads 100k and measures 10k.

Too late! My speaker output wires shorted while testing. Something fried!

[Enzo]

Are you measuring the pot disconnected from the circuit? Or are you measuring it while it is soldered in place? While connected, there will be parallel current paths.

[tigerzilly]

Are you measuring the pot disconnected from the circuit? Or are you measuring it while it is soldered in place? While connected, there will be parallel current paths.

Hey Enzo. You're my hero! I started with a couple Peavey amps and reading threads with your recommendations have been instrumental!

I measured the pot both in and out of circuit. Its currently out of circuit now. See pic. I have a 100k replacement pot in circuit now. Its the reverb pot.

[J M Fahey]

When you do complicated things angry/extremely_tired/in_a_hurry (or all together) shit happens, thatīs why I suggested leaving it aside, at least for some time.

Too late

Pity is that it uses a huge "everything in a single PCB"; IF it had a separate power amp you might junk just that and mount a fresh LM3886 amplifier board, which matches that power supply (+/-25V) but now ...

Oh well.

[tigerzilly]

When you do complicated things angry/extremely_tired/in_a_hurry (or all together) shit happens, thatīs why I suggested leaving it aside, at least for some time.

Too late

Pity is that it uses a huge "everything in a single PCB"; IF it had a separate power amp you might junk just that and mount a fresh LM3886 amplifier board, which matches that power supply (+/-25V) but now ...

Oh well.

Well I wasn't angry, tired, or in a hurry...just careless.

So you're saying everything is fried? Is it time to trash it?

[shortcircuit]

So you're saying everything is fried? Is it time to trash it?

You won't know until you assess how much damage has been done. one step forward, three steps back .

[J M Fahey]

No, I say **the power amp** is fried and given the lack of schematic plus your lack of experience combined that **for now** you canīt repair it.

Leave it aside, maybe on your free time you properly draw then full schematic , no matter how long it takes .

Then in 1/3/6/12 months you post it here and we go on.

Just donīt hurry or get frustrated, that amp is nice and repairable, but we need to go through some intermediate steps.

What I said is we might have saved some time if power amp were on a separate board, because then full replacement was possible; if not then we have no shortcut and must walk the full path.

[tigerzilly]

I wired the vintage Jensen speakers for 8 ohms and installed a 1/4" jack. It makes an awesome sounding 2x12 speaker cabinet!