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Post subject: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 10:12 am
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Joined: Mon Nov 01, 2010 10:31 pm
Posts: 154
Need help in finding out why and how to fix this issue..

Custom Vibrolux Reverb (Printed Circuit), has an issue with the volume.. It seems that there is no real sweep in turning the Bright side Volume knob.. This thing is at 2 and sounds like its at 10!! I went as far as to switch out the Bright side Volume knob with a 250K linear pot and the result was the same.. How can we get this to function properly? Please help!!

The things that have been done to this amp are as follows:
F&T Electrolytic power caps.
JJ Tesla Set of new tubes installed.
Tone stack mod with a .022, .047, and a 250pF silver mica.
100pF silver mica on the Bright Volume from the left to center pins as Fromel does
in his MOD kits.
Reverb tank changed to a MOD three spring tank

Also even with the three spring tank the reverb is still a bit weak for my taste.. Is there anyt MOD that can be done to make it more lively?

Thanks
Pooch


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Post subject: Re: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 11:38 am
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Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
"This thing is at 2 and sounds like its at 10!! "

This sound like a linear pot :lol:

To go slowly you need a logarithmic pot or audio not a linear or B pot . Sound funny hey !

1 M ohms Audio pot as schematic show.


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Post subject: Re: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 12:27 pm
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Even with the factory 1M pot that was in the amp it still had the same effect.. So i figured to change to the other style pot.. Would lowering the resistance of the audio pot make the volume sweep more controllable?


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Post subject: Re: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 1:01 pm
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" Tone stack mod with a .022, .047, and a 250pF silver mica. "

Did the amp have normal range of volume control before the mods? If so, I'd go back and look at your tone stack. Seems that something may have been wired incorrectly.

Or that Bright Switch cap is miss-wired. Try reverting the wiring back to OEM. See if that solves the problem. Then, alter the circuit one-by-one, with each mod. Check for volume issues after each modification.

Good luck! Keep use posted.


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Post subject: Re: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 1:15 pm
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Location: Province de Québec, Canada
BMW2002Ti wrote:


Did the amp have normal range of volume control before the mods? If so, I'd go back and look at your tone stack. Seems that something may have been wired incorrectly.

.



+1


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Post subject: Re: Custom Vibrolux Reverb Volume Issue
Posted: Tue Sep 30, 2014 4:42 pm
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Joined: Fri Jun 20, 2014 2:07 pm
Posts: 303
michaelbpuccio wrote:
Need help in finding out why and how to fix this issue..

Custom Vibrolux Reverb (Printed Circuit), has an issue with the volume.. It seems that there is no real sweep in turning the Bright side Volume knob.. This thing is at 2 and sounds like its at 10!! I went as far as to switch out the Bright side Volume knob with a 250K linear pot and the result was the same.. How can we get this to function properly? Please help!!

The things that have been done to this amp are as follows:
F&T Electrolytic power caps.
JJ Tesla Set of new tubes installed.
Tone stack mod with a .022, .047, and a 250pF silver mica.
100pF silver mica on the Bright Volume from the left to center pins as Fromel does
in his MOD kits.
Reverb tank changed to a MOD three spring tank

Also even with the three spring tank the reverb is still a bit weak for my taste.. Is there anyt MOD that can be done to make it more lively?

Thanks
Pooch


Just to clear, what year is this amp?

I have the new 68 CVR and it's got nice reverb but a little weak compared to the DRRI and TRRI.
I swapped in a 12ax7/ECC83S pre for the OEM 12at7/ECC81, and got a bit more reverb at the same settings as before.

But, the reverb shouldn't be "weak" from this amp.
There is plenty of verb in it. Cranked verb produces a LOT of reverb on this amp.
Maybe something is wrong. Perhaps something is wrong with the send and/or return pre tubes? Swap in some known good ones and take a listen.
If it's not the tubes, then maybe check out the send/return cables from the amp to the spring unit.


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