• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6CG7 Bias Current?

I plan to use a 6CG7 with an Ebb of 240v as the gain stage for a SE 6BQ5 amp. I'm having trouble determining what bias current to use.

I have seen schematics with it as low as 2.3 mA. The datasheet (GE) lists 9 mA as "Typical Operation. The Resistance Coupled chart has Ebb 300v and a R L of .1 meg. That's 3 mA.

When I model it in Tube Cad at about 2.3 mA it says the current is to low and will distort.

What should it be?
Sorry "Idle Current" Newbie mistake. Thanks for the imput. 6-7 mA does seem more logical.

Right now I'm working with the voltages that are calculated when I model the PS in PSU2. I expect (and hope) when I get the amp on the borad, voltages will be higher.

What is CCS Loading? I have seen the term before but haven't researched it. By the way, I'm a tube and electronic Newbie.
Newbie mistake.

Don't worry, a lot of people who aren't exactly newbies are pretty sloppy with those terms as well.

STRONG recommendation: Get a copy of Morgan Jones's "Valve Amplifiers." He covers all of these issues (and many more) very thoroughly and in an extremely readable style. It's absolutely the best investment you can make at this stage in your progress.


2010-02-16 9:00 am
So what should I design to 3mA or something closer to 9mA?

It is most obvious that GE has very carefully considered what data they publish about their products. Therefore I am sure that the data is valid and correct, irrespective of what Tube Cad says.

But what is your idea about your amplifier, how should it perform ?
(gain, input level, used load impedance etc.)
All these have effect to used circuit and bias/current value.