[AMRadio] 813 Triode Connected Bias question.

Paul Baldock paul at paulbaldock.com
Fri Mar 20 22:37:23 EDT 2015

I'm think it will be just a few volts for the 813 triode configuration.

I could figure the voltage by putting a 1K pot in 
the center tap and adjusting it for 20mA, (this 
would allow 20V max). Then when I know the 
voltage, replace the pot with a zener or string 
of diodes with parallel electrolytic.

- Paul

>Hook up  a 9v battery,  reversed, in the 
>center tap of the filament transformer secondary 
>and put some voltage to it.  If that's not 
>enough, add another until you have too much 
>voltage, then wire a pot across the batteries.
>I did this without the pot on a pair of 810's... 
>I think I wound up with 5 or 6 9v batteries 
>strung together for 45 or 50v of bias.
>On Mar 20, 2015 5:16 PM, "Paul Baldock" 
><<mailto:paul at paulbaldock.com>paul at paulbaldock.com> wrote:
>I am building a 2x813 pp triode connected 
>modulator. This means the screen grid and 
>control grid are connected together for each tube.
>I haven't found any characteristic curves for the 813 in this configuration
>On a sample of one, with 0 volts on the grid I 
>measure about 40mA Idle Current (single tube). 
>40mA means about 100W per tube. Does anybody 
>have a guess at what negative bias I would need to reduce this to around 20mA?
>- Paul  KW7Y
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