Blues Jr. reverb problem

Danglin' Fury · 07-03-2009, 03:08 AM

I'm working on an older blues jr.(green board). The guy who previously owned it did some "mods" to it and really screwed it up. I returned everything back to normal but my reverb still has alot of feedback. I went to Bill's blues jr mods and did the reverb mod for the green board. The reverb behaves much better but I can't get it to quit doing the feedback thing. One thing I have noticed is the tank is not original. It doesn't even fit in the amp cabinet. Could there be an impedence mismatch causing this? Is there any way to fix it without having to buy a new tank? Also, when I lay my hand on the reverb springs, the feedback stops. Any help is appreciated.

Twist · 07-03-2009, 04:33 AM

How is the tray mounted....screwed down or in a bag or just hanging?

Enzo · 07-03-2009, 08:10 AM

If it doesn;t fit in the cab, where did they put it?

Feedback is acoustic, not electronic.

The stock BJ reverb is not bagged, it is a short pan, screwd to the botton but with spacers in the grommets so you cannot crank it down tight. Of course if someone removed the brass spacers... Reverbs should never be screwed down tight to the wood. The screws are only in tight enough to keep it from flopping side to side in there.

We can take measures to isolate it from the speaker soundwaves.

Danglin' Fury · 07-03-2009, 07:17 PM

The tank is laying in the bottom in a bag. The feedback occurs even when the tank is lying on the carpeted ground beside the amp. Face up, and when I lay my hands on the springs, they are vibrating. When I push down a little harder, the feedback goes away. Should I just buy a replacement tank or is there a way to fix this. It still feedsback in the bag.

bluesfreak · 07-03-2009, 10:45 PM

Sounds to me like its time for a new (and correctly sized) reverb tank.
If you hesitate check if the coils at the spring ends are not loose, if they are loose it will feedback quite easy...

just my 2c
bluesfreak

HTH · 07-04-2009, 02:21 PM

I would look up the spec for the reverb tray and see if it's supposed to be mounted with the open side of the tray facing up or down.

Also make a note of the input and output impedance and compare them with the in/out impedance of the stock tray listed on the schematic.

Enzo · 07-07-2009, 02:10 AM

The Blues Junior reverb pan is mounted open side down. The only time a pan is mounted open side up is when it is mounted underneath the top of a cab. The proper type is 8EB2C1B.

07-03-2009, 03:08 AM	#1
Danglin' Fury Member Join Date: Jul 2008 Location: Tulsa, Ok. Posts: 45	Blues Jr. reverb problem I'm working on an older blues jr.(green board). The guy who previously owned it did some "mods" to it and really screwed it up. I returned everything back to normal but my reverb still has alot of feedback. I went to Bill's blues jr mods and did the reverb mod for the green board. The reverb behaves much better but I can't get it to quit doing the feedback thing. One thing I have noticed is the tank is not original. It doesn't even fit in the amp cabinet. Could there be an impedence mismatch causing this? Is there any way to fix it without having to buy a new tank? Also, when I lay my hand on the reverb springs, the feedback stops. Any help is appreciated.

07-03-2009, 08:10 AM	#3
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,161	If it doesn;t fit in the cab, where did they put it? Feedback is acoustic, not electronic. The stock BJ reverb is not bagged, it is a short pan, screwd to the botton but with spacers in the grommets so you cannot crank it down tight. Of course if someone removed the brass spacers... Reverbs should never be screwed down tight to the wood. The screws are only in tight enough to keep it from flopping side to side in there. We can take measures to isolate it from the speaker soundwaves. __________________ Education is what you're left with after you have forgotten what you have learned.

07-04-2009, 02:21 PM	#6
HTH Senior Member Join Date: Sep 2006 Location: Newcastle (UK) Posts: 310	I would look up the spec for the reverb tray and see if it's supposed to be mounted with the open side of the tray facing up or down. Also make a note of the input and output impedance and compare them with the in/out impedance of the stock tray listed on the schematic. __________________ HTH - Heavier Than Hell

07-07-2009, 02:10 AM	#7
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 9,161	The Blues Junior reverb pan is mounted open side down. The only time a pan is mounted open side up is when it is mounted underneath the top of a cab. The proper type is 8EB2C1B. __________________ Education is what you're left with after you have forgotten what you have learned.

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07-03-2009, 04:33 AM	#2
Twist Senior Member Join Date: Nov 2007 Location: Springdale, Arkansas Posts: 259	How is the tray mounted....screwed down or in a bag or just hanging?

07-03-2009, 07:17 PM	#4
Danglin' Fury Member Join Date: Jul 2008 Location: Tulsa, Ok. Posts: 45	The tank is laying in the bottom in a bag. The feedback occurs even when the tank is lying on the carpeted ground beside the amp. Face up, and when I lay my hands on the springs, they are vibrating. When I push down a little harder, the feedback goes away. Should I just buy a replacement tank or is there a way to fix this. It still feedsback in the bag.

07-03-2009, 10:45 PM	#5
bluesfreak Member Join Date: Jun 2009 Location: Germany Posts: 65	Sounds to me like its time for a new (and correctly sized) reverb tank. If you hesitate check if the coils at the spring ends are not loose, if they are loose it will feedback quite easy... just my 2c bluesfreak

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