Carvin VTX100 Head Diagnostics Help

[g1]

From the operators manual, sounds like ring is return. So if you plug halfway in and connect to signal generator, you bypass early preamp stages.
The jacks are shown on schematic called 'CH1 Break-In', 'CH2 Break-In'.
You could also plug a cord full way in and scope it. It (tip) will act as a FX send or pre-out to a board, etc.

[glebert]

Should I connect a speaker and see how it sounds?

Just noticed this. Do you have a load hooked up to the output? Tube amps always need a load, either a speaker or something to represent it like a power resistor.

[misterc57]

Yes it is connected to a dummy load. I will be scoping the send and return scenarios next. Thank you!

[misterc57]

Fully inserted phono plug into 'CH1 Break-In'. Connected scope to the phono plug. 1K 500mV sinewave coming off the signal generator.

Sustain switch in the OUT position. Reverb and Drive pots at zero. Master volume at about 20%.

Not a clean sine-wave. Also the peak to peak is not stable and drops after a short amount of time then rises back up.

[misterc57]

Good news! New stuff have come to light!

Channel 2 is working great. Clean sine wave all the way to the output. Last time I checked Channel 2 I did not realize I had to use the Channel 2 input jack, my error.

So Channel 1 has issues that need some debugging,

[glebert]

Nice! Always nice to have one working channel to use as a baseline to compare the broken one to.

[misterc57]

Channel 1 is having issues in the 7 band graphic EQ block.

Signal is going in and not going out. I see this at IC 4558, signal comes in at pin 6, no signal at pin 1, 2 or 3.

I swapped out the 4558 with a NE5532. Problem fixed. Channel 1 is working. Got to love socketed ICs.

Are dual op-amps pretty much interchangeable? I would like to add a few to my next order. Any recommendations on a most commonly used one?

Thank you