[R-390] Receiver Sensitivity

[Jim M.]

Sounds like a clamp in the gear train has loosened or broken.  Do the slugs
move up and down?  If they do check to see that the PTO shaft underneath is
really turning as you tine.  It may be that the clamp on the PTO shaft is
loose and the PTO is not turning, but the preselector gears are, so it shows
best sensitivity at only one spot.

 

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From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Roger Gibboni
Sent: Sunday, February 01, 2009 8:29 AM
To: R-390 at mailman.qth.net
Subject: [R-390] Receiver Sensitivity

 

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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