Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tone Junkie on January 13, 2019, 07:38:34 pm

Title: Cathode bias question.
Post by: Tone Junkie on January 13, 2019, 07:38:34 pm

When going from a single resister per pair. To a single resistor per tube do I halve or double the amount of resistance . example 1- 400 ohm resistor  and cap to 2- 200 ohm resistors and caps.
I seem to have misplaced my notes on this.
Thanks Bill

Title: Re: Cathode bias question.
Post by: sluckey on January 13, 2019, 07:47:21 pm

Quote

When going from a single resister per pair. To a single resistor per tube do I halve or double the amount of resistance

double

Your example is wrong.

Title: Re: Cathode bias question.
Post by: Tone Junkie on January 13, 2019, 10:39:53 pm

Ok Thanks

Title: Re: Cathode bias question.
Post by: jjasilli on January 14, 2019, 08:31:26 am

Actually, you don't need notes.  A cathode R is not a unique situation.  There are no unique situations - instead there is a law of physics.  Ohm's law governs.  The cathode R provides bias voltage (relative to G1).  When current flows through a R, the R causes a voltage drop.  2 Tubes draw 2X the current of 1 tube.  If you halve the current draw through the R, you need to double the R value to get the same voltage drop.