Rich said:
>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.
I didn't make it clear that the 'low impedance' screen supply means low
impedance both for source and sink - i.e good regulation for both source
and sink.. For 6146B's, I use zeners - not ideal, but the screen current
doesn't go very negative - rarely more than 1 or 2mA.
>Stabilizing the grid supply in AB1 is of little value since there is
>neither forward or reverse grid current.
Stabilising has a lot of value if the screen supply is stabilised.
Regulation is the parameter that has little value. Stabilising both is best
to get around mains variations.
Definitions:
'Regulation' is a measure of the variation of output voltage with load.
'Stabilisation' is a measure of the variation of output voltage with input
(mains) variation.
73
Peter G3RZP
"R. Measures"
<r@somis.org> To: "Peter C,"
<peter.chadwick@Zarlink.Com>, "Ian White, G3SEK"
<g3sek@ifwtech.co.uk>
05-Jan-2004 01:31 cc: " AMPS"
<amps@contesting.com>, <amps-bounces@contesting.com>
Subject: Re: [Amps] 3.5 kV 2A
REGULATED Power Supply: Schematic ?
** 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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