Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Latole on September 22, 2020, 05:52:08 am

Title: Twin Reverb 100 watts, volume pots scratch resolve
Post by: Latole on September 22, 2020, 05:52:08 am

The solution has been found. Filter caps

My approach

Problem at the origin; the volume knobs are noisy when turning them and on both channels.
The master volume is correct

1- Contact cleaner; without success (deoxit)
2- All the signal capacitors (coupling) are good and do not let the DC pass
3- New pots are only slightly better.
     I put the old ones back.
4- I intended to replace the old filter caps with F & T
      Once done; no more noise problem at the volume potentiometer

Moral of this story; always replace old filter caps as mentioned regularly

Schematic ;  https://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_sf_100_schem.pdf

Title: Re: Twin Reverb 100 watts, volume pots scratch resolve
Post by: Leevi on September 24, 2020, 07:42:19 am

I have had the same issue sometimes with FMV tone stack. Thank you for sharing this.

/Leevi

Title: Re: Twin Reverb 100 watts, volume pots scratch resolve
Post by: Latole on September 24, 2020, 07:51:48 am

Quote from: Leevi on September 24, 2020, 07:42:19 am

I have had the same issue sometimes with FMV tone stack. The problem is caused by the DC even the caps are fine. Unfortunately I didn't find the reason. 


/Leevi

Did you replace all filter caps ?

Title: Re: Twin Reverb 100 watts, volume pots scratch resolve
Post by: Leevi on September 24, 2020, 08:50:06 am

No, I changed my previous response since you had a solution there. Sorry I did not properly read your message.


/Leevi

Title: Re: Twin Reverb 100 watts, volume pots scratch resolve
Post by: Latole on September 24, 2020, 10:13:53 am

Quote from: Leevi on September 24, 2020, 08:50:06 am

No,

/Leevi

New filter caps may fix the issue