[Johnson] "Viking II C-C" Modulation Saga...

[W4AWM@aol.com]

> As soon as I crank up the mic gain &speak into it, the audio system
> just "takes off"

Hi again Eddie,

You mentioned that you have checked voltages and resistances, but have you 
checked individual resistances and changed all the paper caps in the circuit? 
Haave you checked the mic element and cable, especially the ground 
connections?  On the Astatic "G" stand, if that is what you are using with 
the D-104, there are several places where you could have a bad ground 
connection and be picking up RF.

You say that with the gain control turned to zero, everything is normal.  
With the gain control being at the input to V2, that leaves me to believe 
that the problem is earlier than that, somewhere in the V1 stage or the mic 
or cable. It could be RF pickup causing oscillation.  If there are any 
ceramic caps in the stage, check them, replace any papers, check resistor 
values, the 6AUC and the tube socket.  You will hopefully find the problem 
somewhere there.

Please post yout findings.

73,

John,  W4AWM


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