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Hoffman Amps Forum image Author Topic: Weird voltage problem  (Read 2605 times)

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Offline Leevi

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Weird voltage problem
« on: February 20, 2017, 12:59:12 pm »
I'm modifying a 5F2-A based amp to which I have added tremolo and reverb.
Both tremolo and reverb work fine alone. But when I connect (i.e. solder) voltage
for reverb tube and reverb transformer tremolo stops working, Reverb works always fine.

Actually the circuit is very close to Vibro champ + reverb


http://www.thevintagesound.com/ffg/schem/champ_vibro_aa764_schem.gif


I have tried to take voltage for reverb from different points without success.
I have never met this before,


/Leevi


« Last Edit: February 20, 2017, 01:30:41 pm by Leevi »

Offline sluckey

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Re: Weird voltage problem
« Reply #1 on: February 20, 2017, 01:21:46 pm »
Show us a schematic.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Leevi

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Offline Leevi

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Re: Weird voltage problem
« Reply #3 on: February 20, 2017, 02:06:09 pm »
Updated schematic
/Leevi

Offline pompeiisneaks

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Re: Weird voltage problem
« Reply #4 on: February 20, 2017, 02:38:56 pm »
I think that tremolo works by doing a bias wiggle type change.  The cathode follower on the second half may be impacted by you sharing the same anodes.  I'm not sure of an easy fix, other than maybe you could separate a new B+ line with the same 1k resistor and anew 20uF cap for the reverb section after the first +355V  node? 

Someone with more experience on that may have better insight.
--
Phil Davis
tUber Nerd =|D

Offline Leevi

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Re: Weird voltage problem
« Reply #5 on: February 20, 2017, 02:45:34 pm »
Yes, this is probably the next action I'll do.


Might be that there is a mismatch somewhere


/Leevi

Offline shooter

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Re: Weird voltage problem
« Reply #6 on: February 20, 2017, 05:31:47 pm »
Quote
But when I connect
Measure VDC at C then hook up both and re-measure.

with Both hooked up and reverb pot at 0 and intensity at 10, can you hear any trem?

Went Class C for efficiency

Offline Leevi

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Re: Weird voltage problem, Solved
« Reply #7 on: February 21, 2017, 05:08:37 am »
I found a wrong connection there, my mistake.


I had grounded the reverb tube cathodes to the foot switch point in the tremolo sector
and didn't find that after several checks. There is now so much stuff in a small chassis
that it is difficult to manage.


Thanks for your replies
/Leevi

 


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