** Stabilizing the screen supply with a series pass regulator is not
good engineering practice unless a screen supply bleeder is used to
protect against reverse screen current. Stabilizing the grid supply in
AB1 is of little value since there is neither forward or reverse grid
current.
>I have found problems when using high impedance supplies with 6146s,
>especially as they get older. Especially bad is the Yaesu 'anti flash
>over diode' in series with the screen grid - any negative screen current
>pushes up the screen volts, and the anode current runs away, with
>disastrous results for the valves.
>
>Grid bias and screen supplies should either both be stabilised, or
>neither. If neither supply is stabilised, variations in supply volts tend
>to cancel. I prefer to stabilise them both, and keep the supply impedance
>(at low frequencies, including zero frequency) low. I'm still using the
>original 6146Bs in my FT102, and after 20 years of hard work, they're still
>fine.
>
>73
>
>Peter G3RZP
>
>
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>
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