Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on February 20, 2017, 12:59:12 pm

Title: Weird voltage problem
Post by: Leevi 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 (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

Title: Re: Weird voltage problem
Post by: sluckey on February 20, 2017, 01:21:46 pm

Show us a schematic.

Title: Re: Weird voltage problem
Post by: Leevi on February 20, 2017, 01:26:16 pm

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


/Leevi

Title: Re: Weird voltage problem
Post by: Leevi on February 20, 2017, 02:06:09 pm

Updated schematic
/Leevi

Title: Re: Weird voltage problem
Post by: pompeiisneaks 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.

Title: Re: Weird voltage problem
Post by: Leevi 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

Title: Re: Weird voltage problem
Post by: shooter 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?

Title: Re: Weird voltage problem, Solved
Post by: Leevi 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