Cap to bypass bias battery

dsavitsk · 8th October 2008, 07:06 AM

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 · 8th October 2008, 05:00 PM

Quote:

Originally posted by 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?

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 · 8th October 2008, 08:21 PM

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 · 8th October 2008, 08:38 PM

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 · 24th February 2011, 11:00 AM

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...?

24th February 2011, 11:00 AM	#5
bequerel diyAudio Member Join Date: Sep 2003	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...? __________________ Thanx!

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8th October 2008, 08:21 PM	#3
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	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

8th October 2008, 08:38 PM	#4
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	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

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