[Boatanchors] Grounded Gid Amp Bias?

[Carl]

The TL-922 uses series filaments.

Carl
KM1H


----- Original Message ----- 
From: "Keith Densmore" <densmore at ntl.sympatico.ca>
To: <Boatanchors at mailman.qth.net>
Sent: Saturday, May 30, 2009 7:28 PM
Subject: [Boatanchors] Grounded Gid Amp Bias?


> Hi All,
> I am working on refurbishing  a homebrew grounded grid amplifier. It runs 
> 2
> x  3-500Z's. I would like to be able to cut off the tubes idle current
> during no drive condition but with HV applied.
> I see the Heath SB-200 amp uses a positive bias on the filaments  to cut 
> off
> tube current. I like this idea but here is my question. The way this set 
> is
> wired is that the filament transformer is 10 volts not 5. The center tap 
> of
> the filament transformer is grounded and each of the other two  legs go 
> via
> an rf choke to one side of a 3-500 filament. The two other filament
> connections  are joined, but not grounded. Filament voltage is nearly
> identical on each tube.  My guess is that if I lifted the center tap off
> ground and fed 100 VDC to this point, the tubes will stop conducting. I
> obviously don't want to experiment so maybe someone could tell me if this
> will work, won't work, is insane????
>
> Thanks All,
> 73,
> Keith ve3ts
>
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