Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: KDakaWalt on June 13, 2010, 09:55:52 am

Title: Hammond B3 Percussion Effect
Post by: KDakaWalt on June 13, 2010, 09:55:52 am

I know there are some Hammond B3 folks here. I have been asked by a friend to look at his B3. The percussion effect is weak. It seems to be there when you activate the switch but only momentarily. I plan to replace the tubes in that section first.

I searched and found references to “hair” that can grow on some leads in this section and cause a similar problem, but no specifics.

Any help and guidance is greatly appreciated. KD       

Title: Re: Hammond B3 Percussion Effect
Post by: GroundhogKen on June 13, 2010, 03:12:46 pm

Start here:

http://www.dairiki.org/HammondWiki/PercussionTroubleshooting

Don't be in a hurry to do any zapping.

Schemes:
http://theatreorgans.com/hammond/faq/schematics.html


Ken

Title: Re: Hammond B3 Percussion Effect
Post by: topbrent on June 13, 2010, 03:18:38 pm

Read over this so you can understand the AO-28 preamp:  http://www.bentonelectronics.com/AO28.html

Regarding zinc hair:  http://www.bentonelectronics.com/percussion.html

http://www.dairiki.org/HammondWiki/ZincDendrites

http://www.dairiki.org/HammondWiki/PercussionTroubleshooting

Check/replace the 12au7 tube associated with the percussion effect.

Since you are his repair guy now....read up on, and be prepared to rebuild the scanner someday.  
-   if it isn't giving the helicopter vibrato now......it will be someday.  They all do eventually.

Title: Re: Hammond B3 Percussion Effect
Post by: KDakaWalt on June 13, 2010, 04:31:56 pm

Great info! Thanks so much.  :grin: