Amp Doctors, I Need Your Help Please

Hi there,

Here is a link (I'm trying to figure out how to upload it, but still having trouble). Anyway, my Vox AC15CC1 has been acting poorly. The troubles start around 20 seconds or so.

http://www.youtube.com/watch?v=wosOnkYDxf8

This happens no matter where it's located in the house, no matter which input, guitar or cable I use.

It takes a minute or two of sounding fine until it cuts in, so I'm guessing it has something about the tubes warming up. A while back I had the house to myself and really cranked it up, but not anything extreme, that's the only unusual thing I've really done.....no falls or drops, etc.

I'm hoping it's an easy fix, because any experienced tech is a long way off.

Thanks for any advice....

Do the EL84's glow really red, perhaps with a blue light as well, as soon as the noise starts ? - ie. red plating ??

Hi! Have you built an amp or do you have experience repairing? (I'm new here so don't know if you have a bunch of exp.)
1. Has this ever happened with other amps at your house?
2. Can you swap tubes? New ones or known good ones.
3. If ,and ONLY if, you can drain the power with amp unplugged and know it's safe to poke around (don't forget standby), get a thorough look inside for any cooked parts (resistors or bad caps or whatever).
And that's all I got....(ive not seen inside one, does it have a bunch of chips etc?) Be careful and good luck
I've never heard an amp make that sound, it's like a message from outer space!!!

Thanks for replying guys,

The tubes aren't glowing very red, seems like a normal glow.

I don't have much experience w/ amp repair. but my other amps sound fine in the house. And no parts look fried or anything, so I think I'll re-arrange the tubes, see what happens. If that works or not, I'm gonna order some replacements.

And if ya think that's weird, I used to live in an old building apartment in Champlain, NY. I had a Fender 112 Plus solid state, that would allow me listen to the flight tower in Plattsburgh, 30 miles away.

Thanks again,

Confirm that you have good tubes before going any further, don't guess or assume.
Always start with the simplest solution first and work forward, you can do a lot of damage before you find out it was something simple.
You didn't say whether you knew how to test inside a live amp or not, if not don't do anything. Amps can be very dangerous, sometimes lethal.

Wow, that's a disturbing sound.

Any links or ideas on troubleshooting with a multi-meter? You mentioned confirming good tubes? I'll start Googling and You Tubing!

What I meant was, confirm the tubes are good by having them tested, most of us would swap out known good tubes to confirm a bad tube. In your case you need to find someone with a tube tester. A local electronics store would be a place to start.
Normally in trouble shooting you check:
Inputs
Outputs
Tubes
Yours doesnt sound like it's inputs or outputs
So next is tubes, but you have to be certain that its not a bad tube before moving on.
Neither google or YouTube will be any help in testing your tubes, unless they shw you the nearest place to get tubes tested.

I spend enough time in North Dakota to know you ain't going to find a tube tester or any kind of electronics store. Just buy a new set of tubes and try those you need to have spares anyway.
If you want a tube tester buy another amp. Spare amps make great tube testers.

I spend enough time in North Dakota to know you ain't going to find a tube tester or any kind of electronics store. Just buy a new set of tubes and try those you need to have spares anyway.
If you want a tube tester buy another amp. Spare amps make great tube testers.

:lol:

I'm just gonna have to spend some time on amp forums and get hooked on building those too!

Sure looks like that tube on the right is glowing red to me.

Well I overlooked the North Dakota thing, probably don't have techs around either.
I've lived in Sou Cal all my life so I guess took some things for granted, my mistake.

Heck man if you live in ND you must own an oil well or two just buy a new amp. :lol:
Or stop by on the way to your lake home I'll take a look at it.

No such luck with the oil well. But I do keep pestering my sister to get the MN lake house! Nah, in fact I better go to bed to be a little rested for the j.o.b. in the morning.

No such luck with the oil well. But I do keep pestering my sister to get the MN lake house! Nah, in fact I better go to bed to be a little rested for the j.o.b. in the morning.

Keep us posted on the amp. Try the tube thing first I think that may be it.

Or you could work it into the song. :/

Sounds like some paranormal activity!

Classic symptom of output tubes on their way out. Tubes are like lightbulbs, you have to replace them with fresh ones every so often, because they blow. EL84s wear out faster than other common geetar amp output tubes (to do with their relatively miniature packaging). If you don't replace old worn-out output tubes with a fresh set, then they will eventually get to the point where they cause other problems. In this case you have probably left the old tubes in there too long and one of them is clearly red-plating and has probably already taken out that tube's screen resistor (or worse).

Try a completely new set of EL84s (its better to replace the whole set - if one is bad, chances are the others will be getting there too), but if a new tube red-plates in the same position, then I'd say the damage will already be done elsewhere in the amp, and you'll need to take it to a tech.

Classic symptom of output tubes on their way out. Tubes are like lightbulbs, you have to replace them with fresh ones every so often, because they blow. EL84s wear out faster than other common geetar amp output tubes (to do with their relatively miniature packaging). If you don't replace old worn-out output tubes with a fresh set, then they will eventually get to the point where they cause other problems. In this case you have probably left the old tubes in there too long and one of them is clearly red-plating and has probably already taken out that tube's screen resistor (or worse).

Try a completely new set of EL84s (its better to replace the whole set - if one is bad, chances are the others will be getting there too), but if a new tube red-plates in the same position, then I'd say the damage will already be done elsewhere in the amp, and you'll need to take it to a tech.

Thanks for the good info. I'll be ordering a new set this week. I hope it hasn't got too bad. I never pushed it when the screeching started, just tested different cables, inputs, control levels, etc and shut it back down so the tubes never got too hot. And no tube looked any brighter than the others to me.

I'll post again after a new set comes in and is tried. I'm keeping my fingers crossed. To my ears, humbuckers sound better thru the VOX than my PRRI. And it looks so cool too :cool:

Any news on the new tubes ?