Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: skyclad on May 02, 2010, 02:33:37 pm

Title: Tremolux 6G9 adjustable bias
Post by: skyclad on May 02, 2010, 02:33:37 pm

Tremolux 6G9 (with EL84/6BQ5) has fixed, non-adjustable bias. Also the tremelo runs through the bias circuit. How would you configure a bias adjust control while maintaining the function of the tremelo?

p.s. the layout drawing for 6G9 at schematic heaven shows 6L6gc not EL84 - inconsistent with the schematic.

Title: Re: Tremolux 6G9 adjustable bias
Post by: tubeswell on May 02, 2010, 02:43:40 pm

replace the 56k bias resistor with a 50k pot wired as a variable resistor in series with something like a 27k-39k resistor. Keep the pot wiper shorted to one, or the other (but not both) ends of the pot, so you still have a load if the wiper contact fails.