Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: worth on August 29, 2012, 08:04:16 pm

Title: What's the bias dealio ?!
Post by: worth on August 29, 2012, 08:04:16 pm

Straight Bandmaster build with Dougs 50K bias pot... can't get above 20 ma. I thought with a 50K pot , I could pretty much dial in about anything. I'm using the 470 ohm range resistor.. Heyboer Pt 350-0-350.

Title: Re: What's the bias dealio ?!
Post by: triode on August 29, 2012, 08:29:32 pm

I don't know which bandmaster build you are looking at... but most of the AB763 boards use the 10k pot.

If its the bandmaster AB763, use the 10k, if you want to stick with the 50k, change the bias range resistor.

Title: Re: What's the bias dealio ?!
Post by: worth on August 29, 2012, 08:53:19 pm

AB763 Bandmaster... thought a 50K pot would cover me more than a 10K.

Title: Re: What's the bias dealio ?!
Post by: tubeswell on August 30, 2012, 01:24:41 am

Quote from: worth on August 29, 2012, 08:04:16 pm

Straight Bandmaster build with Dougs 50K bias pot... can't get above 20 ma. I thought with a 50K pot , I could pretty much dial in about anything. I'm using the 470 ohm range resistor.. Heyboer Pt 350-0-350.

Its not just about the range of the pot, its more about where the whole resistive divider for the bias supply is putting the ballpark bias voltage, and what the power source voltage for the bias supply is