Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on July 22, 2016, 10:25:52 am

Title: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: punkykatt on July 22, 2016, 10:25:52 am

http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B12XY.pdf (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B12XY.pdf)

I  did a clean up/routine maintenance, replaced all E caps and out of spec R`s.   Everything on the amp works  and sounds beautiful.  I noticed that when the vibrato is activated and I turn the intensity pot I get a scratchy sound at the beginning and then at the end of the pot rotation. When the vibrato in not activated there is no scratchy sound.  What I have done so far:  Triple clean pot, replace pot, replace cc C-18, 19 & 24.  Scratchy sound still there????  Is that normal for this amp?  Thanks in advance Punky

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: sluckey on July 22, 2016, 11:01:34 am

Does the scratchy sound persist even when you quit turning the knob?

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: punkykatt on July 22, 2016, 12:02:20 pm

No.

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: sluckey on July 22, 2016, 12:31:30 pm

You've already changed all the obvious stuff. I'd just let it ride, ride, ride.

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: punkykatt on July 22, 2016, 12:44:54 pm

Let it ride ride ride.  Thanks Sluckey.  I guess it just is what it is what it is what it is.  I tried.  The customer will have to live live live with it. 

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: PRR on July 22, 2016, 10:24:04 pm

> replace cc C-18, 19 & 24

Replace C8 C10 C11 C12.

Try adding 0.02uFd from pot wiper to ground.

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: punkykatt on July 23, 2016, 01:53:38 pm

PRR, thank you for the suggestions. I tried them, scratch is still there.

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: PRR on July 23, 2016, 03:38:06 pm

Sorry!

I was trying to find ANYthing which could be leaking DC onto the pot wiper. As you had cleaned and changed(?) the pot, DC leak seemed likely. Wish it had helped.

Title: Re: Ampeg B-12XY Scratchy intensity pot (Sluckey) HELP
Post by: punkykatt on July 23, 2016, 06:00:03 pm

Thats ok.  I even tried several pots too, thinking I had defective new.  One of those rare mysteries.  Thanks again. :dontknow: