Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chuggy on October 16, 2011, 01:09:11 am

Title: Two tube switch
Post by: chuggy on October 16, 2011, 01:09:11 am

How can a switch in a twin reverb be wired to select two or four tube operation?
Thanks
Jim R

Title: Re: Two tube switch
Post by: eleventeen on October 16, 2011, 01:51:24 am

The easiest way is to just lift two of the cathodes from ground. Make sure they are 6L6's on opposite sides of the output tranny. (duh)

If the amp is stock, just an SPST switch will do. If the tube cathodes are sitting on top of custom-installed bias-check resistors, then you should use a multiple pole switch and keep the cathodes of the lifted tubes separate.

I have done this, by the way, without drilling additional chassis holes by using a center-off switch (eg; a 3 position with a detent in the middle) which is the AC switch on one half and 2/4 cathode switch on the other half. The switch ends up being
(1) AC on 40 watts /
(2) AC off /
(3) AC on 80 watts.

Title: Re: Two tube switch
Post by: stratele52 on October 16, 2011, 03:19:52 am

Quote from: eleventeen on October 16, 2011, 01:51:24 am

. Make sure they are 6L6's on opposite sides of the output tranny. (duh)


  ??? 

Use both outside  ( V7, V10 ) or both inside tubes, ( V8, V9) or one inside and one outside  ( V7, V9 or V8,V10) . Tubes must stay in pushpull operation