Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fred on April 03, 2020, 03:38:36 pm

Title: Vibro champ ? Switch on intensity pot
Post by: fred on April 03, 2020, 03:38:36 pm

Hi , I have a pot switch on my deluxe reverb  . when turned off it gives the amp more gain , would this mod work on a  vibro champ .
Its a 80s black  face
Thanks for any input
Fred

Title: Re: Vibro champ ? Switch on intensity pot
Post by: shooter on April 03, 2020, 04:05:23 pm

Quote

when turned off it gives the amp more gain

from what I see on the schematic you should get the same "gain" with the pot on 0 and no switch.

Title: Re: Vibro champ ? Switch on intensity pot
Post by: sluckey on April 03, 2020, 06:07:33 pm

Quote from: fred on April 03, 2020, 03:38:36 pm

Hi , I have a pot switch on my deluxe reverb  . when turned off it gives the amp more gain , would this mod work on a  vibro champ .

No. The deluxe reverb tremolo circuit is quite different than the VC circuit.

Title: Re: Vibro champ ? Switch on intensity pot
Post by: fred on April 03, 2020, 06:19:13 pm

Thanks for the fast answer back.

Title: Re: Vibro champ ? Switch on intensity pot
Post by: shooter on April 03, 2020, 06:37:14 pm

Guess I missed something
"Switch on intensity pot"
does it short to ground the intensity pot, like if pot set to 0?  :dontknow:

Title: Re: Vibro champ ? Switch on intensity pot
Post by: fred on April 04, 2020, 10:47:36 pm

Hi , my understanding is the intensity pot turns off all passing electric , gain and increases gain in the pre tubes .
Something about the regular stock pot takes away some gain from the preamp tube circuit even on 0 .
So on a deluxe reverb if you have a switched pot and it's turned off it adds gain .
I was lookin at the vibro champ wiring , it's not as complex as the deluxe is .
So thanks for the input ..

Title: Re: Vibro champ ? Switch on intensity pot
Post by: sluckey on April 05, 2020, 06:25:02 am

The 50K INT pot in the AB763 amps puts a heavy load on the signal path. When you disconnect the INT pot with the switch the signal increases because the 50K pot is no longer loading the signal. This results in the signal boost. Of course you no longer have tremolo. This is a popular mod for the AB763 amps.

The VC trem circuit is quite different and this switch mod will not work.

Title: Re: Vibro champ ? Switch on intensity pot
Post by: shooter on April 05, 2020, 08:20:22 am

Quote

puts a heavy load on the signal path

my missing link, thanks  :laugh:

Title: Re: Vibro champ ? Switch on intensity pot
Post by: fred on April 05, 2020, 09:44:34 pm

Thanks sluckey you explained it well .
It is a great mod on the deluxe reverb . I also have the NFB control , called soul control . and if you pull v1 it adds more gain too .
Amps are amazing .
Sluckey , I have that 1940 National amp all up and working great . the field coil does sound nice . I did the rat nest wiring .
It's not pretty , but looks like the 1940s  . thanks again