Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on May 21, 2021, 09:59:32 am

Title: Traynor bass amp running hot/bias resistor
Post by: Diverted on May 21, 2021, 09:59:32 am

Hi,

How would I increase the negative bias in this Traynor bass amp? It's non-adjustable fixed bias and currently the 6AC7s are running at about 80 percent. Would I want to reduce the 33K (R32) just prior to the bias diode, or would I be better off adjusting the 47K (R31) after the diode? Thanks.

Title: Re: Traynor bass amp running hot/bias resistor
Post by: sluckey on May 21, 2021, 10:16:31 am

Put a 50K pot in series with that 47K.

Title: Re: Traynor bass amp running hot/bias resistor
Post by: Diverted on May 21, 2021, 10:48:43 am

Can't do a pot on this one, he doesn't want it. So instead, I guess just try upping the value of that resistor ... maybe 51K, 56K, etc.? Thanks for the tip.

Title: Re: Traynor bass amp running hot/bias resistor
Post by: sluckey on May 21, 2021, 10:57:13 am

Tell him that he may have to go through this every time he changes tubes unless he submits to the pot.   :icon_biggrin:

Changing the value of a resistor is just as much a mod as adding a trim pot.   :think1:

Title: Re: Traynor bass amp running hot/bias resistor
Post by: 2deaf on May 21, 2021, 11:03:42 am

Quote from: Diverted on May 21, 2021, 10:48:43 am

Can't do a pot on this one, he doesn't want it. So instead, I guess just try upping the value of that resistor ... maybe 51K, 56K, etc.? Thanks for the tip.

My money is on 51K.

36K in series with a 25K pot if you want to go that route.