...you misunderstood the schematic: the bias generator is supplying bias
just to the 2 opamps in order to set the trip reference.
The tube is controlled by the IRF 540 as a two state switch only, moving the
tube from STDBY to operate.
For setting the bias you need either a negative voltage source, like we did
with the dual 6146, or else connect a zenner in series with the cathode AND
the FET. Don't try to read in the schematic something that isn't there:
it'll only confuse you.
Get a copy of Will Orr's book: you have plenty of examples on how to.
BTW concerning the silver strip: guys, drop the nonsense! There is not
anything better than good old plain copper strip cut from flashing copper.
It will tarnish a bit in 20 years' time, so what?
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Radio WC6W
Sent: Wednesday, July 09, 2008 7:45 PM
To: amps@contesting.com
Subject: [Amps] A Grounded Grid biasing question
Has anyone ever seen a design wherein an 8877, or similar triode, operated
in grounded grid has the bias generator placed in the grid return line,
rather than in the typical cathode (grid + cathode current) location?
This implies that the HV return must be allowed to float at least as
positive as the bias value. The grid remains chassis grounded as usual. And
the advantage of this arrangement is that the bias generator need only pass
the grid current which is typically 1/10 of the cathode current.
A proposed circuit may be seen at:
http://wc6w.50webs.com/wc6wamps/index.html?fr40.html
73 & Good morning,
Marv WC6W
http://wc6w.50webs.com/
*
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