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Post subject: Amp cutting out?
Posted: Fri May 14, 2010 5:18 pm
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Hello all! Can't seem to figure out why my amp is cutting in and out. Sometimes she'll work great all day and other times the volume just goes all the way down and rarely comes back up:( Is this a problem within the amp? Problem within the electronics of my guitar? Cheap, expensive? Any advice will help guys thanks!


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Posted: Fri May 14, 2010 5:21 pm
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Sounds like a power tube going out. I'd look there first....Hope this helps....... 8) Mike

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Posted: Fri May 14, 2010 5:34 pm
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What model amp???

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Posted: Fri May 14, 2010 7:17 pm
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Vox Valvetronix AD15VT

If it were a power tube what would that run me?


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Posted: Fri May 14, 2010 8:19 pm
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stratattak wrote:
Vox Valvetronix AD15VT

If it were a power tube what would that run me?

only one tube in the valvetronix. 12AX7 in the preamp... and trust me, it ain't the tube.
these amps are very finicky. i had an AD60VT that was giving me the same trouble. if you're running it from a power strip, yank the plug out and plug it directly into a socket that has nothing else plugged into it. voltage is the key to these buggers. if your manual says the amp draws 120V and your outlet is only delivering 115 it'll drop out.
i got tired of fiddling and diddling. last gig i did, the light guy plugged his setup into my strip (which i had only my amp plugged into). immediately my amp started dropping out. managed to get it going... ran through the first set... second set - nothing. lucky i had my 25W FENDER automatic with me as a back-up.

too bad. i really loved the sound of that amp, but i had to click the vox on and off sometimes 10 or 15 times to have it make noise. i traded it in last week for a fender hot rod deluxe. turn it on, it's on, i can hear my strat and tele loud and clear. play it every day and it doesn't drop out.

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Posted: Fri May 14, 2010 8:21 pm
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From what I see it uses a 12AX7 (ECC83) dual triode valve. They're usually under $20.

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Posted: Sat May 15, 2010 12:06 am
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Thanks a lot guys this has helped a lot!


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Posted: Sat May 15, 2010 9:05 am
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No problem. Your amp is pretty much a hybrid. It may or may not fix the problem, but I think the tube would be the weakest link in the chain.
I don't know much about hybrid amps, they're strange beasts. Vox has this in the manual.

"The Valve Reactor power stage is, to all intents and purposes, a bona fide valve (tube)
push-pull power amplifier, but in miniature. It utilizes a 12AX7 (ECC83) valve (a dual triode
device — meaning “two valves in one”) and is equipped with an output transformer,
just like a “real” valve amp."

I'm not getting it. Maybe Art or Arjay know something about them.

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Posted: Sat May 15, 2010 9:37 am
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A old Marshall Valvestate I had years back did the same thing. Output transformer was on the decline. I tried a valve swap and noticed that all the drive channel still worked without the 12ax7 in. The clean channel didnt work at all without the valve in.
Yet it was marketed as a hybrid amp with a real ecc83 valve to give that unmistakable marshall drive. And a Bipolar output transformer that responds the same way a valve power amp would.

Bipolar eh??? :lol:

In truth it wasnt that bad, there was a good bit of compression added as the volume control was turned up.

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Post subject: Re: Amp cutting out?
Posted: Tue Feb 25, 2020 7:12 pm
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I have a Super Sonic 60 head on a matching 4 x 12 cabinet that will occasionally drop out and the jewel will go out while the channel indicator lights stay on and, if I give it a whack on top, like the Fonze, it'll turn back on. I opened it up a couple of times and looked at the fuse just before the jewel only to find that it was fine, all before I discovered that I could just whack it. Second time in my life I made that discovery I suppose... anyway, I'm going to take it to my tech and get him to check it out while installing new tubes. I'm not sure if it needs tubes but it can't hurt. Maybe upgrade it a bit from the GTs in it.


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