Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bugman3183 on January 18, 2021, 01:26:17 pm

Title: Extend bias range
Post by: Bugman3183 on January 18, 2021, 01:26:17 pm

Hello all,. Recently came into possession of a 68' custom deluxe reverb, and decided to swap the gz34 with a 5y3 ( just personal preference).  Using a probe (type that goes between socket and tube)  the highest I can adjust the tubes to is 12 ma.  My question is can I increase the range of bias by lowering the value of r59 from 22k to around 15k or so.  Or is there something else that needs to be done.  Thank you.

Title: Re: Extend bias range
Post by: sluckey on January 18, 2021, 02:03:59 pm

Quote

can I increase the range of standby by lowering the value of r59 from 22k to sound 15k or so

Yes. I would not go below about 10K.

Title: Re: Extend bias range
Post by: Bugman3183 on January 18, 2021, 02:21:44 pm

Thanks for the reply slucky.  I'm cracking up at myself after reading my post( damn auto correct).  I've edited the post and it's hopefully easier to follow now.

Title: Re: Extend bias range
Post by: glass54 on January 18, 2021, 03:43:41 pm

Hi Bugman
You could fit 1R Metal Films on Cathodes (Pin 8) on V7 and V8  :icon_biggrin:
Really easily monitoring of currents without fitting/removing probes.
Kind regards
Mirek