[AMRadio] Modulator feedback


Rick Brashear rickbras at airmail.net
Thu Mar 16 22:42:54 EST 2006


I've posed a couple of questions on some other lists and received some 
good advice, but I am still in need of more.  My BC-610-E has a bad 
feedback or "talk back" problem.  I've placed a capacitor across the 
overload relay (RY-5) and that did eliminate a little of the talk back.  
However, with much audio gain at all, not nearly enough to attain 100% 
modulation, I get feedback.  Not just talk back, but feedback.  I have 
to assume it's coming from the modulation transformer.  The modulator 
bias is set for 40 ma as specifications state.  The bolts on the 
modulation transformer are all tight.  What am I over looking here?  I'm 
using a BC-614-E speech amplifier with a D-104 non amplified mic.  I did 
a few modifications to the dynamic input circuitry of the BC-614 to 
better match the D-104, but that is the only modification in either the 
speech amp or the BC-610-E.

Rick/K5IZ





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