Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: catnine on July 04, 2011, 09:14:37 pm

Title: Since I raised the value of the cathode bias resister from 470 ohm to 680 ohm
Post by: catnine on July 04, 2011, 09:14:37 pm

to get my AA764 champ to set the 6V6 at close to 14 watts , this is when the line voltage is the highest I get here which is 118.5 VAC , if the line is 115.2 the 6V6 runs at close to 13 watts. I did raise the bias cap to a higher voltage cap yet I read that some even use a high value cap , instead of 25 uf they use a 50 uf . What does the higher uf cap do in this position , pass more lows like it would on the bias of the 12ax7 cathode?

Title: Re: Since I raised the value of the cathode bias resister from 470 ohm to 680 ohm
Post by: phsyconoodler on July 05, 2011, 10:30:00 am

It allows more of all frequencies to pass.It may tighten up the bass a tad,but you really won't notice much until you up the bypass cap to about 500uf or more.
  I've used as high as 1000uf and they sound great.I've tried ever increment of cap from 25uf to 1500uf and it depends on the amp as to what you get out for tones.
  Experiment and listen to the differences.

Title: Re: Since I raised the value of the cathode bias resister from 470 ohm to 680 ohm
Post by: Tone Junkie on July 05, 2011, 03:17:37 pm

Thanks phyconoodler once again I have learned something usefull related to tube amps. If I wanted to build a switchable cap box just to test these out what would be you recomended voltage for the cap, 100volt.
thanks Bill
PS. gotta love this place