Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blueznet on August 15, 2011, 09:41:57 am

Title: 25K - RA POT?
Post by: blueznet on August 15, 2011, 09:41:57 am

Trying to replace a worn out intensity pot on a 67 Fender Vibro-Champ.

Anyone know of a Vendor that would carry this pot? I looked at Doug's pots and he does not have them.

I have searched for the 25K Reverse Audio and can't seem to find one either.

Thanks,
Darrell

Title: Re: 25K - RA POT?
Post by: John on August 15, 2011, 10:43:23 am

http://www.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=184223688 (http://www.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=184223688)

If Mouser doesn't have 'em, dunno who would. Good luck!

Title: Re: 25K - RA POT?
Post by: jeff on August 15, 2011, 12:19:11 pm

There's a way using a bigger pot with a resistor to "trick" a linear pot into thinking it's a reverse audio pot. It won't be exactally the same thing at full rotation but it may a way to get a better responding control if you can't find a RA pot.

Good luck.

http://www.geofex.com/article_folders/potsecrets/potscret.htm (http://www.geofex.com/article_folders/potsecrets/potscret.htm)

Title: Re: 25K - RA POT?
Post by: blueznet on August 16, 2011, 07:10:42 pm

Can't believe why no one has the 25k RA pot. Would a 50k RA work for the intensity on this Blackface Vibro-Champ?

Title: Re: 25K - RA POT?
Post by: OldHouseScott on August 17, 2011, 12:24:59 am

Yes, it should work fine. You might want to change the cathode resistor it's connected to down to 47k to keep the total resistance at about 100k when cranked all the way up, but it's not necessary.

Title: Re: 25K - RA POT?
Post by: stratele52 on August 17, 2011, 03:46:45 am

blueznet , you can't fix the pot ?

Title: Re: 25K - RA POT?
Post by: blueznet on August 20, 2011, 06:45:25 am

Quote from: OldHouseScott on August 17, 2011, 12:24:59 am

Yes, it should work fine. You might want to change the cathode resistor it's connected to down to 47k to keep the total resistance at about 100k when cranked all the way up, but it's not necessary.

You mean the 68k down to 47k?

Title: Re: 25K - RA POT?
Post by: OldHouseScott on August 22, 2011, 08:02:50 am

Yes, that's the one, although it's not strictly necessary to change it.