Cap to bypass bias battery

[dsavitsk]

I am using 2x 9V batteries in series to bias the grid of a tube to 18V. Should I bypass the batteries with a capacitor, and if so, what value would people recommend?

 

[kevinkr]

I am using 2x 9V batteries in series to bias the grid of a tube to 18V. Should I bypass the batteries with a capacitor, and if so, what value would people recommend?

I usually use something in the range of a few uF, to avoid cap leakage currents from running the batteries down I generally use low voltage films for this. It may take a combination of several caps in parallel to achieve the best results..

 

[Gluca]

well my experience is that I don't need any cap ... but I am deaf. I tried many caps (type and value) but couldn't notice any difference

OH! Me too, I am using 2x9V to bias 211's.

Gianluca

 

[bigwill]

I would personally put a resistor in series with the battery (outside of the loop of the transformer and load resistor)

So then it just becomes a high impedance biasing source

 

[bequerel]

Speaking of battery bias. This schematic which comes from the site of Troels Gravesen uses a battery in series with the grid. I have also seen this type of bias arrangement in a linestage or phonostage from an American company.

What are the voltage requirements of the cap that bypasses the battery?
Is it full B+, only a few volts, or...?