[R-390] Receiver Sensitivity

Roger Gibboni rgibboni at dulye.com
Sun Feb 1 08:29:16 EST 2009


Hey- I could use some help. Picked up a Collins 390a and when I powered it
up on the bench, the sensitivity was terrible-between 200 and 700
microvolts. So I started checking the usual stuff; tubes, front end
alignment, etc---nothing. Then while I was tuning and testing, I found that
the receiver had good sensitivity---less than 1 microvolt at 3.88 MHZ. Only
at that frequency! 100KHZ either way and the sensitivity died. So I checked
the frequency alignment of the 2nd LO and that seemed fine. It would also
appear that the lower 3/4 of the 0 MHZ band is dead---really dead!

Needless to say, I'm at a little bit of a loss here. I should also add that
this radio had a Miltronix makeover (well done) so I see that caps, etc have
already been replaced.

Thanks- Roger WA3YTM

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