[Amps] hf-2500 again

[TexasRF at aol.com]

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 at 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 at arrl.net> mailto:k1ttt at 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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