Vox AC50 CPain in the &^%

[drewl]

That's what the "P" must stand for.

This is a brand new unit, fresh out of the box.

Okay, had no reverb, no FX return, and no voltage on the footswitch 'ring" connector which is used to power the reverb LED on the footswitch, or "B" control.

First, there's a little mod where the input jack grounds the input to the 4th preamp tube, so no FX return unless there's something plugged into the input.

The reverb switching voltage was being dragged down by a bad circuit board trace running too close to the FX send ground. It was marked with some kind of red ink, but nothing was done about it, so I had to cut the trace and rerun a wire to the footswitch jack.
I've seen the FX/reverb/low voltage power supply board have problems with older units where the traces have shorted or the pc board material had broken down/become conductive.

And lastly the reverb signal was being loaded down by some type of foreign material inside the channel two reverb pot, loading the reverb signal line down to about 30 Ohms.

Since the reverb pots for both channels are tied together it was killing the reverb to both channels.

Hope this helps some other idiot.

[Jazz P Bass]

Yowza!

[soundguruman]

I have found that pretty much all of them need to be entirely re-soldered.
Other than that, looks like you found other fun stuff.

The name badge says: "Vox" But the inside is nothing like a real Vox...

[Gtr_tech]

Its nothing more than a new Mar$hall inside. *Any* amp that is ROHS needs to be resoldered to be reliable.....

[g1]

there's a little mod where the input jack grounds the input to the 4th preamp tube, so no FX return unless there's something plugged into the input.

Saw the same issue in another amp last year, sorry I can't recall right now which make and model. It had one of the input jack switch terminals running to a mute circuit at the FX return. So you couldn't use the power amp by itself without sticking a dummy plug in the input jack.
Very annoying when you are trying to narrow down whether a problem is in the preamp or power amp. I guess they don't expect anyone to be using the power amp separately, but it makes for a bit of a diagnostic headache.