[R-390] break-in question, 390A and 390

[Don Heywood]

Hello All, I have been reading all the recommended fixes for using the R-390 
family in conjunction with a transmitter, opening RF GAIN, removing B+ etc.
The BREAK-IN circuit is all you need. On transmit a ground is applied to the 
rear terminal board Pin 9, and with the BREAK-IN Switch ON, the break in 
relay not only grounds the antenna but another set of contacts grounds the 
audio.  I used an R-390 with my KWS-1 several times on the 20M CCA net.
73
Don WC4G

No copyright, just RDFM
----- Original Message ----- 
From: "2002tii" <bmw2002tii at nerdshack.com>
To: <r-390 at mailman.qth.net>
Sent: Monday, July 25, 2011 2:03 PM
Subject: Re: [R-390] break-in question, 390A and 390


>
>>Would it be worthwhile to dump the B+ when in break-in mode or is the 
>>decay
>>of the B+ potential too slow to be effective?
>
> Not a good idea for multiple reasons.
>
> If you have modified the AGC to have a fast attack characteristic at
> all AGC speed settings, you can isolate the AGC circuit from the AGC
> line with a decently high resistance or some diode logic and bang the
> AGC line to, say, -50 V during tx to cut off the RF and IF.  The AGC
> circuit will recover to full gain during tx (since no signal is
> getting through the RF/IF to develop AGC voltage), but the fast
> attack of the modified AGC will do a fair job of suppressing the
> noise burst when you return to rx mode, and you can always sequence
> the AF muting to stay on a little longer to mask it.
>
> If you have not modified the AGC, the procedure above won't work so well.
>
> You can avoid having the AGC recover to full gain by clamping the
> pre-tx AGC circuit voltage with a sample-and-hold so it takes up
> where it left off when you release the AGC line clamp -- some newer
> SS radios did just that -- but adding sample-and-hold circuitry to a
> 390 would be way too kludgey for my taste.
>
> Best regards,
>
> Don
>
>
> Copyright (c) 2011.  Not for redistribution.
>
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