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Fender Twin - Crazy Squeal!! What??
Old 21st December 2010
  #1
Lives for gear
 

Fender Twin - Crazy Squeal!! What??

Whoa.... okay.... my heart is still pounding. I plugged my fender twin reverb reissue into the wall just now, and flipped on the power. Waited an appropriate 30 seconds or so and flipped on the standby. I had my little labs red eye "reamp out" plugged into the input, being fed by a line level signal down the chain. Immediately when I flipped it out of standby, it made a crazy squeal / siren sound I've never heard in my life. *So* very loud. The channel volume was all the way down to zero. (I performed an idiot check and the volume wasn't all the way up or anything. Fully off.) Frantically I dove for the power switch and killed power as quickly as possible. (siren noise "winds down", dropping in pitch and volume until it's off a few seconds after I killed the power)

Regroup.

Okay, my LL is wired through some newly-configured patchbay routing, so I figure maybe I made a mistake in the wiring. Alright, unplug the 1/4" input from the amp. Nothing plugged in.... nervously, I reach for the power switch. Engaged. Wait a little bit, doublecheck that all reverb and gain knobs on both channels are fully down, and flip it out of standby. Regular "amp in idle" sound, slight noise, normal sound. I reached for my little labs to plug it back in, and bump it *slightly* against the top of the amp, on the tolex - squeal again! I don't think the LL had anything to do with this, but *WTF*?

I'm terrified to try again - that noise was truly horrific, especially at 2am. Maybe I'll grab my earplugs and work up the courage during the day tomorrow to do some further testing.

In the meantime, has anyone experienced this? I mean, WTF??? I can't describe how loud and jarring this sound was.

Thanks in advance!

(ps: I've had this amp for about a year and it's been fine, no major issues. Light duty with a handful of gigs, mostly in my studio though, not a ton of hours on the amp)
Old 21st December 2010
  #2
Lives for gear
 

PS I'm thinking it's got something to do w/ the reverb unit in the amp.... like the reverb gain is up very very high and feeding back. I dunno, just an instinct. When you bump this amp the reverb can rattle around some, but if its level was really high for some reason it'd feedback like this??
Old 21st December 2010
  #3
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Most likely cause is that one of your valves has gone microphonic, most likely a preamp valve. Get a new valve and swap them out one by one, starting with the first one in the signal path. Or, wear some earplugs, turn up the amp a little and gently tap each preamp valve one by one with a pencil......you'll soon find the problem if it's a microphonic one

First place to check for almost any problem is the preamp valves, then the power valves; although it is unusual that it squealed with the gains turned down.

http://www.geofex.com/ampdbug/ampdebug.htm
Old 21st December 2010
  #4
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Fender Twin - Crazy Squeal!! What??

Quote:
Originally Posted by timlloyd
Most likely cause is that one of your valves has gone microphonic, most likely a preamp valve. Get a new valve and swap them out one by one, starting with the first one in the signal path. Or, wear some earplugs, turn up the amp a little and gently tap each preamp valve one by one with a pencil......you'll soon find the problem if it's a microphonic one

First place to check for almost any problem is the preamp valves, then the power valves; although it is unusual that it squealed with the gains turned down.

http://www.geofex.com/ampdbug/ampdebug.htm
Thanks for the input! I will research further tomorrow with my -20db sensephonics in lol

Just to be clear, the input gains were *fully* down! So strange. I turned it on again after my previous post (wearing some closed-ear cans) and didn't have the squeal. But I wasn't brave enough to leave it on for more than 10 seconds....

So far, the problem has only happened with the LL present nearby - it sounds crazy but is it possible the LL and the twin are affecting eachother by physical proximity without being connected? I feel silly just saying that - surely can't be right??

I think I have some spare ax and at7s around, will try to reproduce the problem and try replacing tubes.

With microphonic tubes is it common to have a fully turned down amp squeal at what seemed like maximum possible volume? I don't understand how that could even happen...
Old 21st December 2010
  #5
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Scott Whigham's Avatar
 

Crazy! That would scare the bejeebus out of me lol. I'd be rattled as hell for hours.

If you plug your headphones into the reamp out jack on the Red Eye, do you get that squeal?

Can you play your guitar through the amp when plugged directly in without issues?
Old 21st December 2010
  #6
Lives for gear
 

Quote:
Originally Posted by rcb4t2 View Post
With microphonic tubes is it common to have a fully turned down amp squeal at what seemed like maximum possible volume? I don't understand how that could even happen...
I've never had an audible microphonic valve with all gains off, but I'm not sure.....it might be possible. It's the part about you bumping the top of the amp that makes me think it's a valve-gone-rogue. It could also be a loose solder joint shorting against something, and the bump could have tweaked the connection.

Quote:
Originally Posted by rcb4t2 View Post
So far, the problem has only happened with the LL present nearby - it sounds crazy but is it possible the LL and the twin are affecting eachother by physical proximity without being connected? I feel silly just saying that - surely can't be right??
I don't know....they both have transformers in, which are magnetic. Though I'm also not sure if it's possible that they could affect each other, let alone enough to cause that loud of a problem.
Old 21st December 2010
  #7
Gear Maniac
Quote:
Originally Posted by timlloyd View Post
Most likely cause is that one of your valves has gone microphonic, most likely a preamp valve. Get a new valve and swap them out one by one, starting with the first one in the signal path. Or, wear some earplugs, turn up the amp a little and gently tap each preamp valve one by one with a pencil......you'll soon find the problem if it's a microphonic one

First place to check for almost any problem is the preamp valves, then the power valves; although it is unusual that it squealed with the gains turned down.

Tube Amplifier Debugging Page
Definitely do this! You also have preamp tubes in your amp that are specifically made to drive your reverb. Check those too. This problem definitely sounds like a microphonic tube issue. Good thing is that 12ax7 and ECC83 tubes are fairly cheap. Best of luck in getting it fixed.
Old 21st December 2010
  #8
Gear Addict
Do you have the Reverb knob turned up at all? If something was wrong there, you would still hear it even if your gain knob(s) were all the down.

Make sure the cables are seated firmly in the reverb unit itself.

Dan
Old 21st December 2010
  #9
Lives for gear
 

Consider yourself lucky when my twin goes it starts smoking and then something inside explodes. It's normally a cap and the pcb needs to be fixed. Every time I get it fixed it costs 400 dollars. Every time it explodes and I get it fixed it sounds better and better though. Great amps well worth the up keep.
Old 22nd December 2010
  #10
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Well, so far I haven't been able to reproduce the problem today. After a few nervous moments starting it up today there was no abnormal noise. I plugged a guitar in with nothing else involved and it worked fine, sounded normal. I hooked up my LL the way I was intending to last night and it worked fine - didn't change any patch connections either. Played for about an hour straight with no issues....

This is almost worse, now it's a waiting game to see if it crops up again... (and I'm sure it'll wait until an important session to rear its ugly head.... )

I happened to speak to an amp tech today and he said it sounded like a problem with the reverb unit - that the connectors can become corroded to the point where intermittent contact is being made. I haven't actually gotten in the amp to check this out - I just felt back there and the plugs are fully inserted, not loose at all.

When I get a moment I'll try to inspect individual tubes and connections and see if there are any visible suspects.

While we're on the twin..... any suggestions for taming the percussive / bassy sound? I know that's part of the sound, but it's not always desirable....
Old 22nd December 2010
  #11
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Quote:
Originally Posted by Beefy View Post
Consider yourself lucky when my twin goes it starts smoking and then something inside explodes. It's normally a cap and the pcb needs to be fixed. Every time I get it fixed it costs 400 dollars. Every time it explodes and I get it fixed it sounds better and better though. Great amps well worth the up keep.
Yikes! This one is just a reissue of the '65 - made in '03 I think but not 100% sure. Is yours an original?
Old 22nd December 2010
  #12
Lives for gear
 

I date mine at like 94 or 95 lol. They will be considered vintage classics of the reissues 30 years down the road.

Seriously though for the priced of 500 used and 900 dollars since I have spent on repairs. I can't get it's tone anywhere else (custom explosions) and 15 years of great service. It's way more than a deal on an amp that sounds exactly the way I want.
Old 21st March 2017
  #13
Here for the gear
Speaking of Twins. I have a 75 Silverface which has been blackfaced. Due to its age, from day one of me having it, theres always been a considerable level of white noise which doesnt bother me as when the amp is being played all I hear is the beautiful sound of my guitar working with it, however as of last week, upon releasing standby , its now making a very peculiar sound or two, the first is the sound of something like a powerplant reactor or something powering down, not volume related, just about standard volume and it turns into a staggered kind of beating sound and gets slower and slower, it usually eventually stops but from there on sporadically there is an awful sort of "wind in a condensor mic" sound and some "tape recorder like sqeaking" sounds that proceed to invade the amp. Does anyone have any clues at what that might be. I'm near certain its a job for an amp specialist, my real concern is cost. Could it be the capacitor? My level of knowledge inept of basic. Any suggestions or info would be much appreciated as this amp is a collector and I pain to think it will need major surgery. Many Thanks
Old 21st March 2017
  #14
Gear Addict
 
Jake's Avatar
 

Quote:
Originally Posted by Dave Mallon View Post
Speaking of Twins. I have a 75 Silverface which has been blackfaced. Due to its age, from day one of me having it, theres always been a considerable level of white noise which doesnt bother me as when the amp is being played all I hear is the beautiful sound of my guitar working with it, however as of last week, upon releasing standby , its now making a very peculiar sound or two, the first is the sound of something like a powerplant reactor or something powering down, not volume related, just about standard volume and it turns into a staggered kind of beating sound and gets slower and slower, it usually eventually stops but from there on sporadically there is an awful sort of "wind in a condensor mic" sound and some "tape recorder like sqeaking" sounds that proceed to invade the amp. Does anyone have any clues at what that might be. I'm near certain its a job for an amp specialist, my real concern is cost. Could it be the capacitor? My level of knowledge inept of basic. Any suggestions or info would be much appreciated as this amp is a collector and I pain to think it will need major surgery. Many Thanks
I have no idea, but the beating sound makes me think it might be something in the tremolo circuit?

I wouldn't hesitate to take a SF twin in for service as they tend to be some of the least expensive amps to service and repair. I've owned a '73 SF Twin for 20 odd years and have had it serviced numerous times, I don't think I've ever spent more than $200 - $300 on it.
Old 22nd March 2017
  #15
Here for the gear
Yo Jake

Quote:
Originally Posted by Jake View Post
I have no idea, but the beating sound makes me think it might be something in the tremolo circuit?

I wouldn't hesitate to take a SF twin in for service as they tend to be some of the least expensive amps to service and repair. I've owned a '73 SF Twin for 20 odd years and have had it serviced numerous times, I don't think I've ever spent more than $200 - $300 on it.
Hey Jake, cheers bro. The thing is, it does it after standby is released and then kinda drops slowly and evenly in pitch until its at a beating pulse kind of speed. I used bright channel and normal channel but it makes no diff. Ive contacted an amp technician and as you say, its better to have it seen by them and serviced and or repaired as these amps are too important to allow to rot not that any or most of us in the ownership of 40+ year amps would do but money is not everyones strength. Im fortunate in as much that i have the money to do it but I may not eat for a month to fix this issue. Ho hum, amp comes first ☺️
Old 22nd March 2017
  #16
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enorbet2's Avatar
All runaway oscillation us caused by a positive feedback loop, whether mechanical or strictly electrical. Seek and destroy the loop and oscillation is nipped in the bud. This is what a qualified tech will do by process of isolation and elimination.

Last edited by enorbet2; 23rd March 2017 at 11:07 AM..
Old 22nd March 2017
  #17
Quote:
Originally Posted by rcb4t2 View Post
Whoa.... okay.... my heart is still pounding. I plugged my fender twin reverb reissue into the wall just now, and flipped on the power. Waited an appropriate 30 seconds or so and flipped on the standby. I had my little labs red eye "reamp out" plugged into the input, being fed by a line level signal down the chain. Immediately when I flipped it out of standby, it made a crazy squeal / siren sound I've never heard in my life. *So* very loud. The channel volume was all the way down to zero. (I performed an idiot check and the volume wasn't all the way up or anything. Fully off.) Frantically I dove for the power switch and killed power as quickly as possible. (siren noise "winds down", dropping in pitch and volume until it's off a few seconds after I killed the power)

Regroup.

Okay, my LL is wired through some newly-configured patchbay routing, so I figure maybe I made a mistake in the wiring. Alright, unplug the 1/4" input from the amp. Nothing plugged in.... nervously, I reach for the power switch. Engaged. Wait a little bit, doublecheck that all reverb and gain knobs on both channels are fully down, and flip it out of standby. Regular "amp in idle" sound, slight noise, normal sound. I reached for my little labs to plug it back in, and bump it *slightly* against the top of the amp, on the tolex - squeal again! I don't think the LL had anything to do with this, but *WTF*?

I'm terrified to try again - that noise was truly horrific, especially at 2am. Maybe I'll grab my earplugs and work up the courage during the day tomorrow to do some further testing.

In the meantime, has anyone experienced this? I mean, WTF??? I can't describe how loud and jarring this sound was.

Thanks in advance!

(ps: I've had this amp for about a year and it's been fine, no major issues. Light duty with a handful of gigs, mostly in my studio though, not a ton of hours on the amp)

Quote:
Originally Posted by rcb4t2 View Post
PS I'm thinking it's got something to do w/ the reverb unit in the amp.... like the reverb gain is up very very high and feeding back. I dunno, just an instinct. When you bump this amp the reverb can rattle around some, but if its level was really high for some reason it'd feedback like this??
Probably a microphonic tube. The possibility that it might be reverb related is easy to test - turn the reverb down. If that doesn't affect the noise it's something else. Most likely neither V1 or V2 has gone microphonic. Pull the one at a time and see if the problem goes away. Try tapping on the other tubes, saee if it affects the noise.

There are other things that could cause a similar problem but they're beyond your capability to test, so if none of the above work, take it to a tech.
Old 22nd March 2017
  #18
Quote:
Originally Posted by rcb4t2 View Post
Well, so far I haven't been able to reproduce the problem today. After a few nervous moments starting it up today there was no abnormal noise. I plugged a guitar in with nothing else involved and it worked fine, sounded normal. I hooked up my LL the way I was intending to last night and it worked fine - didn't change any patch connections either. Played for about an hour straight with no issues....

This is almost worse, now it's a waiting game to see if it crops up again... (and I'm sure it'll wait until an important session to rear its ugly head.... )

I happened to speak to an amp tech today and he said it sounded like a problem with the reverb unit - that the connectors can become corroded to the point where intermittent contact is being made. I haven't actually gotten in the amp to check this out - I just felt back there and the plugs are fully inserted, not loose at all.

When I get a moment I'll try to inspect individual tubes and connections and see if there are any visible suspects.
Tap on the tubes with a pencil and seer what happens.

I've never heard reverb wiring cause a squeal, and if it did it would not happen with the reverb turned off.

Quote:
While we're on the twin..... any suggestions for taming the percussive / bassy sound? I know that's part of the sound, but it's not always desirable....
Turn down the bass knob?
Old 22nd March 2017
  #19
Quote:
Originally Posted by Dave Mallon View Post
Speaking of Twins. I have a 75 Silverface which has been blackfaced. Due to its age, from day one of me having it, theres always been a considerable level of white noise which doesnt bother me as when the amp is being played all I hear is the beautiful sound of my guitar working with it, however as of last week, upon releasing standby , its now making a very peculiar sound or two, the first is the sound of something like a powerplant reactor or something powering down, not volume related, just about standard volume and it turns into a staggered kind of beating sound and gets slower and slower, it usually eventually stops but from there on sporadically there is an awful sort of "wind in a condensor mic" sound and some "tape recorder like sqeaking" sounds that proceed to invade the amp. Does anyone have any clues at what that might be. I'm near certain its a job for an amp specialist, my real concern is cost. Could it be the capacitor? My level of knowledge inept of basic. Any suggestions or info would be much appreciated as this amp is a collector and I pain to think it will need major surgery. Many Thanks
I've encountered this kind of noise problem before - it's usually a sign that the amp has been worked on by a monkey.

It seems that there are a lot of idiots around who have the mistaken impression that blackface Fenders have increased gain and/or preamp distortion/boost, so they monkey around with the gain structure to make the amp "hotter", which has the effect of increasing the noise, often to an unbearable (to me, anyway) degree. A few months ago I had to rebuild a Bassman that had been "blackfaced" by one of those bozos. I found front end mods that made NO sense and had nothing to do with real blackface circuitry. Interestingly enough he had done nothing to the phase inverter and power amp stages to do a real conversion to blackface spec (which is a bit difficult on the early '70s Bassman, as the layout of the eyelet board does not match the AB763 circuit.)

I ripped out his "mods" and spent the better part of a week figuring how to implement the correct changes on the present circuit board (layout is critical on Fender tube amps.) Put it together, noise gone, amp worked great.

As to the new noise, it's a sign that your amp needs recapping. The thing is, changing the coupling caps can change your tone, so it's best to change only the ones that need changing. Changing the power supply caps and cathode (all electrolytic) caps won't so don't hesitate to replace those.

The "wind" type sound is probably tube related - either a tube going intermittently noisy from age or a dirty/loose contact in a tube socket.

Last edited by John Eppstein; 22nd March 2017 at 10:47 PM..
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