[AMRadio] BC-610 talk-back

[D. Chester]

> Let's be a little more definitive. A noisy relay that has an almost 
> constant sound is not "talking" back.? A transformer/reactor that has 
> noise that follows the voice is "talking" back.? Relays do not "talk back" 
> but in all fairness, I have had some really noisy ones that I cured by 
> converting over to DC with a diode and small cap.? Hope this cleans the 
> conversation a little, hi.
>
> Mel, K6KBE

The overload relay in the BC-610 may indeed talk back with modulation.  The 
relay coil that triggers the overload function is wired in series with the 
HV DC plate supply on the negative side, to cause it to pull in whenever the 
total current drawn from the supply exceeds a pre-set level (via adjustment 
of a wire-wound rheostat in parallel with the coil).  In phone mode, the 
modulated DC passing through  the coil results in talk back that follows the 
voice.  Putting the capacitor from mid-tap of the plate transformer to 
ground by-passes the coil for audio, but still allows the full DC to pass 
through  the coil.

A lot of people assume the talk-back is from the modulation transformer, 
when that may not be the cause.  It is very unlikely that the potted 
versions of this transformer would talk back.

If that same relay is chattering with a constant buzz and not following the 
voice, there must be other issues.  A bad filter cap maybe? Or perhaps 
another relay in the transmitter that runs off 60~ a.c.?

Don k4kyv

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