The modulation/delay crashed on my vox valvetronix vt40, the amp sound from the guitar, disappeared. Everything else works. What to do?
Do the lights of the channel selectors still work?
If so, change the tube in the amp - whatever 12AX7 would work, it's only a buffer and it alters the sound veeery little.

If they don't then factory-reset the thing, and then substitute the tube if the amp still doesn't work.
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All lights works. And I have restarted couple of times. If I connect my cd player through the line in socket, no problem it sounds, same if i put on the headphones. But no guitar sound. The only thing is that the modulation/delay switch "filtron" have no light, and "tape echo" switch turn on the light and stays red, no matter what I do. The rest of the effects work, even though they mixed themselves up, they came up on the wrong place. This started the day before the amp stopped work. And the tube, seems fine.
"Seems fine" and "actually fine" are two different things. It could be fried and you wouldn't know it from first glance.

Your problem definitely sounds like it's the 12AX7. I think the out ports bypass the 12AX7. Replace it. c:
Last edited by Will Lane at Feb 18, 2015,
Actually I doubt it's the tube. The tube in that amp isn't a regular maintenance thing like a regular tube amp, I really don't think all that much is required of that tube. If there's no sound out of the amp but you do get sound out of headphones I would think the speaker cable/wire has a short. It could be something to do with the headphone jack as well, maybe its not bypassing it. I don't know, I'm not a tech and I'm just guessing but I would take it as an excuse to get a new amp anyways.
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Well, the tube "glows" orange as always...and there is sound from the speaker when the amp is connected to the cd player. The tuner works. The sound stops" somewhere in its way to the speaker.