David, it sounds like the cutoff bias is not operational. Most amplifiers
have a resistor in series with the zener bias that develops cutoff bias when
in standby. Then a relay or solid state switch shorts that out when in
transmit leaving only the zener bias.
Maybe whatever took out the original zener bias also damaged the cutoff
switching circuit like welded relay contacts or shorted switching transistor.
Without cutoff bias you can expect some broadband noise while receiving.
This is a total guess on my part as i have no direct experience with your
amplifier model.
73,
Gerald K5GW
In a message dated 4/20/2013 7:33:30 A.M. Pacific Daylight Time,
K1TTT@ARRL.NET writes:
Ok, got parts in and replaced most of the bias circuit. Now I have 9.7v
on
the cathode on rx and 8.7v on tx. Would those be reasonable for bias when
cutoff and tx in ab2 operation for the pair of 3cx800a7's?? I have a
feeling the cutoff voltage is a bit low as I am seeing a bit of plate
current, at least its just barely moving the needle instead of the 400ma I
had before.
David Robbins K1TTT
e-mail: <mailto:k1ttt@arrl.net> mailto:k1ttt@arrl.net
web: <http://wiki.k1ttt.net/> http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or <telnet://k1ttt.net/> telnet://k1ttt.net
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