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

[rbethman]

That's why I commented over the weekend about using my Johnson T-R 
switch and the Break-in circuit.

Also, run the SM-220 Monitor w/BP-8 from the R-390A IF out.

I watch what is going out, see what the signal looks like coming in, and 
the T-R Switch handles what the BC-610 can dish out.

Bob - N0DGN

On 7/25/2011 3:28 PM, Don Heywood wrote:
> 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.
>>
>>
>>
>>
>>