[AMRadio] Modulator feedback

Rick Brashear rickbras at airmail.net
Fri Mar 17 20:58:43 EST 2006

Thanks Don.  I used a 100 uf capacitor at 160 vdc, so it should be 
sufficient.  I hooked it up exactly as you stated, positive to ground 
and the negative lead toward the center tap of the HV transformer.  I 
wish I could say it stopped it, but I still have problems.  It did stop 
a lot of the talk back, but the feed back is still there albeit not 
nearly as prevalent since I switched the 2A3 driver tubes.  I made a 
couple of modifications to the dynamic microphone input to better 
accommodate the non amplified D-104, but I can't see how that would have 
anything to do with it.  I can move the mic several feet away (it has a 
long cord - possibly too long) and turn the audio up enough to get 100% 
modulation on the scope.  The 614 has a pretty high output and it takes 
little to overdrive the modulator.


Donald Chester wrote:

> How much capacitance did you use?  It should be at least 20 mfd.  A 
> cheap electrolytic should do ok, since there is only a few volts 
> across it.  Put it between the midtap of the plate transformer and 
> ground.  The positive side should go to ground, and the negative side 
> to the transformer.  In all the BC-610E's I have ever seen, that 
> capacitor eliminates 95% of the chatter.
> Don k4kyv
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