Twin Reverb Reverb issue

djbarker · December 21st, 2006, 03:50 PM

I've got a beat up old SF Twin Reverb that I've put a bunch of work into that now sounds fantastic. However, I've lately been having some issues with the reverb. With the bass up the spring tank rattles to the point that it's almost unlistenable. Additionally, with the reverb cranked I get a feedback that doesn't go away unless I turn the reverb off. That is, I can have the guitar volume all the way down and the feedback persists. Any ideas of what might be up?

TY · December 21st, 2006, 09:28 PM

Sometimes a microphonic reverb driver tube will howl on its own. Swap some tubes around and see if it helps.

Welcome to the board.

djbarker · December 21st, 2006, 10:34 PM

Thanks TY - can I simply switch them or do they need to be replaced with something that isn't microphonic? If I just need to switch them, does it matter which 12ax7 I switch them with?

Telenator · December 22nd, 2006, 06:56 AM

It doesn't matter as long as the tubes are all 12ax7's. If I recall that amp may have a couple 12at7's in it which look exactly the same but will not sound the same.

I agree with TY, it's probably just a microphonic tube.

Stan Martin · December 22nd, 2006, 08:24 AM

should be a 12AT7 not AX7, the recovery tube should be a 12AX7. Also the phase inverter is a 12AT7.

djbarker · December 22nd, 2006, 10:56 AM

Thanks everyone - this is some great help for my first post. What about the rattle I'm getting? It's pretty much an exaggerated version of the sound you get when you stomp the floor next to an amp with a spring reverb. I can't play the wound strings without that noise when the reverb is on.

Stan Martin · December 22nd, 2006, 05:02 PM

some foam weather stripping to the tank cardboard bottom(shock absorber) and put back in the bag, also do NOT tighten the reverb bag down all the way. There needs to be some freedom of movement, if the bag is tightened down all the way, then every little motion will trigger the springs to rattle.

stevedenver · December 23rd, 2006, 05:46 PM

Quote:

Originally Posted by Stan Martin

some foam weather stripping to the tank cardboard bottom(shock absorber) and put back in the bag, also do NOT tighten the reverb bag down all the way. There needs to be some freedom of movement, if the bag is tightened down all the way, then every little motion will trigger the springs to rattle.

exactly

djbarker · January 9th, 2007, 11:17 PM

I have done the weather stripping trick - worked beautifully. Unfortunately, the squeal with the reverb still persists at high reverb settings. I checked out the tubes, they're all a-okay. I've heard a couple of ideas from techs around. It's either: a bad reverb tank (looked good to me when I had it out of the bag to add the weather stripping), corroded reverb tank lead(s), or the reverb transformer. Let me know what you think.

Clive Hugh · January 9th, 2007, 11:57 PM

I just had a similar thing with my Fender twin, the guy replaced the reverb transformer plus something else but it fixed it, it's the second time I have had the transformer go like that.

December 21st, 2006, 03:50 PM	#1 (permalink)
djbarker NEW MEMBER! Join Date: Nov 2006 Location: Wisconsin Posts: 8	Twin Reverb Reverb issue I've got a beat up old SF Twin Reverb that I've put a bunch of work into that now sounds fantastic. However, I've lately been having some issues with the reverb. With the bass up the spring tank rattles to the point that it's almost unlistenable. Additionally, with the reverb cranked I get a feedback that doesn't go away unless I turn the reverb off. That is, I can have the guitar volume all the way down and the feedback persists. Any ideas of what might be up?

December 22nd, 2006, 06:56 AM	#4 (permalink)
Telenator Friend of Leo's Join Date: Sep 2005 Location: Connecticut Posts: 4,403	It doesn't matter as long as the tubes are all 12ax7's. If I recall that amp may have a couple 12at7's in it which look exactly the same but will not sound the same. I agree with TY, it's probably just a microphonic tube. __________________ Dogs have the right idea!

December 22nd, 2006, 08:24 AM	#5 (permalink)
Stan Martin Tele-Holic Join Date: Mar 2003 Posts: 799	the reverb driver tube should be a 12AT7 not AX7, the recovery tube should be a 12AX7. Also the phase inverter is a 12AT7.

December 22nd, 2006, 05:02 PM	#7 (permalink)
Stan Martin Tele-Holic Join Date: Mar 2003 Posts: 799	add some foam weather stripping to the tank cardboard bottom(shock absorber) and put back in the bag, also do NOT tighten the reverb bag down all the way. There needs to be some freedom of movement, if the bag is tightened down all the way, then every little motion will trigger the springs to rattle.

December 21st, 2006, 09:28 PM	#2 (permalink)
TY Tele-Meister Join Date: Mar 2003 Location: Hell-A Posts: 304	Sometimes a microphonic reverb driver tube will howl on its own. Swap some tubes around and see if it helps. Welcome to the board.

December 21st, 2006, 10:34 PM	#3 (permalink)
djbarker NEW MEMBER! Join Date: Nov 2006 Location: Wisconsin Posts: 8	Thanks TY - can I simply switch them or do they need to be replaced with something that isn't microphonic? If I just need to switch them, does it matter which 12ax7 I switch them with?

December 22nd, 2006, 10:56 AM	#6 (permalink)
djbarker NEW MEMBER! Join Date: Nov 2006 Location: Wisconsin Posts: 8	Thanks everyone - this is some great help for my first post. What about the rattle I'm getting? It's pretty much an exaggerated version of the sound you get when you stomp the floor next to an amp with a spring reverb. I can't play the wound strings without that noise when the reverb is on.

January 9th, 2007, 11:17 PM	#9 (permalink)
djbarker NEW MEMBER! Join Date: Nov 2006 Location: Wisconsin Posts: 8	I have done the weather stripping trick - worked beautifully. Unfortunately, the squeal with the reverb still persists at high reverb settings. I checked out the tubes, they're all a-okay. I've heard a couple of ideas from techs around. It's either: a bad reverb tank (looked good to me when I had it out of the bag to add the weather stripping), corroded reverb tank lead(s), or the reverb transformer. Let me know what you think.

January 9th, 2007, 11:57 PM	#10 (permalink)
Clive Hugh Tele-Holic Join Date: Sep 2006 Location: Western Australia Age: 63 Posts: 529	I just had a similar thing with my Fender twin, the guy replaced the reverb transformer plus something else but it fixed it, it's the second time I have had the transformer go like that.