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

[2002tii]

>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


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