[AMRadio] Modulator feedback

Mike Sawyer w3slk at uplink.net
Fri Mar 17 15:47:44 EST 2006

    Unfortunately, you are plagued with the same problem dozens of -610 
owners have. The only way to resolve it is to get an I or H model modulation 
transformer. They are potted and hermetically sealed and don't talk back 
near as much. Other than that you are SOL.
----- Original Message ----- 
From: "Rick Brashear" <rickbras at airmail.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Thursday, March 16, 2006 10:42 PM
Subject: [AMRadio] Modulator feedback

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.


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