Bill,
A much better way to deal with your 811a amplifier would be to ground the
tube grids with a low inductive straps, have a relay in the filament
center
tap with a large value resistor >50k in series. The relay shorts the
resistor
out of the circuit in the transmit mode. Cutoff for the tube(s) is
developed by
the voltage drop across the resistor in receive. A stud mount type
(high
watt) zener is often used to set the resting Ip. Metering of the grid
and plate
current is also done in this path. Much safer, no extra -B vdc supply
required.
Been doing it that way for many years...
cheers
skipp
:
{snip}
From: Bill Smith <shadow1@jnlk.com>
I'm confused. I've installed a Negative Bias supply in the amp and am
supplying about -100vdc to the 811A grids. The plate current as
indicated
on the meter is still 100ma. If I remove the negative bias from the
grids(ground it out) the plate current increases to about 120ma. The
manual says the "Resting Plate Current" is supposed to be 100ma. In the
troubleshooting section of the manual one cause of improper resting plate
current was noted as not grounding the bias terminal on the rear apron,
effectively removing the negative bias. I did this and the plate current
went up to 120 ma from 100ma. My question is: Is the HV inducing the
resting plate current and can not be removed by apply a negative bias to
the grid? I'm learning the hard way, trial and error.
73,
Bill KO4NR
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