[AMRadio] Modulator feedback


Rick Brashear rickbras at airmail.net
Fri Mar 17 16:25:01 EST 2006


Wow!  Not exactly the news I wanted, Mike, but thanks for the honesty.   
It looks like I may have to move the speech amp and mic considerably 
further away from the "E" model.  I have an "H" and "I" model, but they 
are still in the refurb process.  Potted  modulation transformers or any 
modulation transformer for the 610 series is scarce.  I have a UTC that 
will work, but it's not potted and I have an oil filled military 
transformer that would work if I had room on the chassis.  I wonder what 
the guys in the SCR-399 did to contend with this issue since they were 
in such close quarters?  Anyway, back to the drawing board and thanks 
again for the info.

73,
Rick/K5IZ


Mike Sawyer wrote:

>Rick,
>    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.
>Mod-U-Lator,
>Mike(y)
>W3SLK
>----- 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.
>
>Rick/K5IZ
>
>
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