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Post subject: '73 Fender Twin Reverb acting strangely and making odd noise
Posted: Sun Jul 31, 2011 9:35 am
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Hello, I have a Twin Reverb that I've had for almost a year now. The amp was serviced back in 04 by the previous owner, and had just about everything gone over and touched up. I haven't had any problems with it at all.

Then a couple days ago, I got some NOS RCA and Raytheon preamp tubes at a sale. The guy I bought them from had marked on the boxes which tubes were good, and I made sure I only bought the 'good' ones. However, when I put them in the amp, it was really noisy, and the reverb wouldn't work anymore. I figured it was just the 12aT7's, and I replaced them with the tubes that had been in there. Worked a lot better, but there was still no reverb.

Then yesterday, after I'd been playing for about 30 minutes or so, there was this sort of bubbly leaking sound and a very strong chemical smell (sort of like rotten eggs or something). I turned off the amp and let the room vent. I turned it back on this morning to see if it was any better. The bubbly sound occurred just about as soon as the amp warmed up. I looked in the back, and there's this sort of pink wax that seems to have dripped from the small transformer by the 3rd preamp tube.

I just turned it on again, and left it on for about 5 minutes after it warmed up, and the reverb 'works'. I can hear it being overloaded by the pops and clicks and noise of the tubes, but it won't take a signal. Also, the bubbling noise is really loud now, and continues after the amp is shut off. I won't be turning it on again for a while.

Any help or advice is really appreciated. I know that this is a big post, but I figure that more info is better than not enough info.


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 9:41 am
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i would unplug the amp and not turn it back on until you've taken it to a competent Fender amp guy.

With a '73, your electrolytic filter caps are due to change; you may have had one pop as they can burst with age, possibly taking out components downstream. Turning the amp back on may have damaged more, but the only way to tell is by taking it to an amp tech.

If you post where you're from I'm sure you'll get some great recos on Fender amp repair shops.

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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 9:52 am
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Offhand it sounds like one of those "RCA or Raytheon" 12AX7 is shorted-out. A 12AX7 is used in the reverb circuit to "recover" the reverb tone. The "tranny" you mentioned is prolly the one that is coupled to the reverb circuit. Is it small and angled at 45-degrees, on the chassis?

Anytime you see ANY kinda ooze coming outta trannies or near filter cap areas.. it's bad news. Never turn the amp on until the issue is resolved. :(

Like Neo said, you need a good amp tech now. Sorry, couldn't be much help. Good luck with your amp.

(BTW: I would call the seller of those tubes. And NOT used any of the ones you bought, until they are fully tested, by another person. Not the seller).


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 9:55 am
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Fried reverb tranny.

This has happened to me three times over some 45 years. It's an easy task to replace and -- usually -- no other components were damaged when the tranny took a dump. You can find a replacement on Ebay for reasonable money.

HTH

Arjay

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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 10:15 am
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Thanks for all the help. I asked my dad, who used to be into electricity before he retired, and he says that the dripping is from the transformer getting to hot. He then said the only way that it would get too hot is from a short. Which is most likely from one of the tubes. 3 of the 12AX7A's are RCA, 1 12AX7 is a GE, then the 2 12AT7's are Raytheon.
Although, the last tube line-up in there was kind of weird. 3 JJ ECC83S, 2 Sovtek 12AX7A, 1 EH 12AT7.

I'm pretty sure it's not the caps. All the caps were replaced back in 04, and the amp hasn't seen all that much action anyways.

I'll look into a replacement transformer (it is the one at a 45 degeree angle), but I won't be doing anything with the amp until I know for sure. Looks like it's playing through the dumpy little back-up I have.

Thanks again.


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 10:47 am
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You might also yank the doghouse and see what filter caps lie beneath. If they're IC's I'd drop-kick them into the nearest dumpster and replace with some quality Sprague's or better yet, F&T's.

JMO, YMMV, KDTTAH, etc.

Arjay

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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 11:00 am
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AFiestofFriends wrote:
I'm pretty sure it's not the caps. All the caps were replaced back in 04, and the amp hasn't seen all that much action anyways.

Looks like it's playing through the dumpy little back-up I have.

Thanks again.
Well if the amp has not seen much action gives you all the reason to put new caps in there.If they are not used the chemicals inside of them harden up and short out an burst and make funny smells.That's why some of the cleanest vintage amps are some of the worst sounding ones.

But is does sound like your problem is the reverb transformer is shot.They really don't cost that much.Sounds like a shorted tube fried the tranny


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 12:30 pm
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Do caps really go bad that fast? I figured it'd take at least a decade or two, not 6-7 years.

Is the doghouse the metal cover immediately behind the preamp tubes?


And I looked at a replacement on ebay? Does brand matter much, or do they all perform the same?


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 1:51 pm
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I've had brand new 'lytics go bad. Of course you never really know how long they sit on a vendor's shelf before he sells them to a tech or you. So your 6-7 year old caps may really be 15 years old.

If an amp has been sitting unused for awhile, it's a good idea to reform the caps using a Variac or old light bulb trick. They can be more vulnerable to early failure, if not reformed. It doesn't hurt. I use a Variac with all amps on first fire up. Even on newly re-capped ones. It's also a good way to detect shorts and other issues before they fry your amp's guts.

That all said and done... I still think you got a bad 12AX7. As it fried the reverb section, only. At least from your description of the meltdown. But, it won't hurt to go through the amp. Esp with that much current flowing during the short. To see if other parts didn't get hurt. Unfortunately, you can have a 12AX7 short out and eat a section--- but not have the fuse blow. As it's really set to blow for bigger current shorts in the power sections (power supply and power tubes). 1-2 amps RMS through a gain stage or EFX stage can be enough to cook that section.

Good luck with your amp. Keep us informed.

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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Sun Jul 31, 2011 2:55 pm
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BMW2002Ti wrote:
That all said and done... I still think you got a bad 12AX7.


Possible. Probable, even. Whenever a tranny drips spooge all over a chassis it's a sure sign that something has gone seriously south. A runaway 12AX7 could be just the culprit.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: '73 Fender Twin Reverb acting strangely and making odd n
Posted: Mon Aug 01, 2011 2:41 am
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NEVER put power tube without checking bias


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