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Fender Quad Reverb issues
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Fargonof
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#1
5th February 2013
Old 5th February 2013
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Fender Quad Reverb issues

A while back i bought a Fender Quad Reverb, and when i got home the vibrato channel produced some horrid broken speaker-esque distortion when you pushed the preamp past about 4. I took it to a shop to get it fixed, but they told me that it was caused by how the circuit was designed.

According to them, the reverb/vibrato pulled a bunch of energy since they are never properly bypassed, hence the problem-free normal channel. Now i'm pretty new to the tube amp game and i don't know much about electrical engineering or circuitry, but that just sounds weird to me. If it's an inherent flaw in the design, why haven't i read about it anywhere? It's a pretty respected amp doctor, but it just sounds absurd to me.

I've found one guy on the entire internet with a similar problem, it doesn't seem like a common thing. Does anyone here mind enlighting me on whether or not it's fixable? It's pretty frustrating since i can't use any amp distortion at all
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5th February 2013
Old 5th February 2013
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I have a Quad here and no problems. Not sure what your amp guy is talking about. If I want amp distortion this is not my first choice. I normally use this amp when I want a creamy/drippy type of sound. This one is a 70's Quad and my amp tech has no problem fixing anything on it. (so far)
Good luck!
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5th February 2013
Old 5th February 2013
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If you haven't already tried different tubes in it, I'd try that. Otherwise, I'd find a different tech.
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5th February 2013
Old 5th February 2013
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Yep, the tech you took it to has no idea what they're talking about. Avoid him.

Fender Quad Reverb is the same circuit (mostly) as the Showman and Twin; the tremolo is an optoisolator. They do wear out, but are available here:

Black Widow Tremolo Bug [Black Widow] - $26.00 : Austin Amplifier, Custom Guitar Amplifiers, Parts and Repair


I'd also substitute a known good 12AX7 in V5, which in that amp is the tremolo tube.

Properly biased and checked for the usual (dried out filter caps, etc.), a 70's Quad Reverb will give you lots of Fender clean.

If you post your location, people may be able to suggest competent amp techs who know silverface Fender amps. Another great resource is the Fender Forums (FenderĀ® Forums • View forum - Vintage Guitar Amplifiers (anything before 1985)) and for specs on your amp, Ampwares: Fender Silverface Twin Reverb | Ampwares (yours is the same except it's a 4x12 instead of 2x12).

If you haven't already, I'd get a convertible hand truck for transport - your back will thank you.
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#5
6th February 2013
Old 6th February 2013
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+1 on getting a new tech - this amp(quad) is a twin w/ 4x12's
Fargonof
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6th February 2013
Old 6th February 2013
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Quote:
Originally Posted by nedorama View Post
Yep, the tech you took it to has no idea what they're talking about. Avoid him.

Fender Quad Reverb is the same circuit (mostly) as the Showman and Twin; the tremolo is an optoisolator. They do wear out, but are available here:

Black Widow Tremolo Bug [Black Widow] - $26.00 : Austin Amplifier, Custom Guitar Amplifiers, Parts and Repair


I'd also substitute a known good 12AX7 in V5, which in that amp is the tremolo tube.

Properly biased and checked for the usual (dried out filter caps, etc.), a 70's Quad Reverb will give you lots of Fender clean.

If you post your location, people may be able to suggest competent amp techs who know silverface Fender amps. Another great resource is the Fender Forums (FenderĀ® Forums • View forum - Vintage Guitar Amplifiers (anything before 1985)) and for specs on your amp, Ampwares: Fender Silverface Twin Reverb | Ampwares (yours is the same except it's a 4x12 instead of 2x12).

If you haven't already, I'd get a convertible hand truck for transport - your back will thank you.
Thank you all for confirming this, i thoght it sounded like a funky explanation. I'm located in Stockholm, i do know of another amp tech that is pretty well respected but i'll take any suggestions.

And yeah, i'm planning on finally getting that drivers license because of this amp, it's just ridiculously heavy!

Also, i've tried switching the preamp valves around with a new 7025, as well as switching the set tubes around to see if maybe one of them was worn out, but it didn't realy do anything. It seems improbable that it would be the power section concidering the normal channel works just fine.
#7
28th February 2014
Old 28th February 2014
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Ronalda is offline
quad reverb problems

I have had a 70's quad reverb for about 22 years but didn't use it untill a few years ago. It had some rumbling problems which I had fixed but then a little over a year ago while playing at low volume all of the output power seemed to get sucked out of the amp. I had it at my tech for over a year and he can't figure it out. It seems all voltage and current are correct if you bypass the choke, but replacing it didn't fix the problem. He said he checked all caps and bias circuit, which he had previously blackfaced. Still can't find the problem, he said it's the first time he has failed to fix any amp and is completely puzzled. Transformers check good, all caps good, changed the choke twice and still the same. Desperate to find an answer, any ideas ?
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