[R-390] Got my R-390A working great.

[Larry H]

Dave,  Good deal on all those nice receivers.  And, good work on getting
your A working.  Those pesky caps will do it every time.  Did you replace
the C553 (filter killer cap)?  One thing to consider about which one to
keep would be that the A has a lot of spare parts available.

As for the stiff IF transformer cores, any powder that would absorb
moisture would not be good (IE: talcum, etc.).  Any liquid that the coil
form could absorb would also not be good.  I've used powdered graphite with
good success.  Be careful with too much torque on the cores, as that can
split them.

Have fun.

Regards, Larry



On Sat, Nov 30, 2019 at 5:41 AM David Olean <k1whs at metrocast.net> wrote:

> Hello BA enthusiasts
>
> I have been slowly working on getting an R-390A running.  I was side
> tracked for a short time with some carpentry, but had everything working
> except the carrier meter. The meter was pegged to the left at all times.
> Funny thing because when I first started work on the R-390A, that meter
> worked. (?)  Well I finally got some time to work on it again, and found
> the problem with the meter,  a bad bypass cap in the cathode circuit of
> the 4th IF amplifier. I did not suspect it as this was a 1967 EAC
> contract unit and it had modern poly caps in it. Of course I assumed
> those new looking parts were fine and so I looked everywhere else at
> first.   The shorted cap looked like a 3 ohm resistor.
>
> After getting everything running, I decided to tweak up the IF
> transformers. Just about every slug was badly stuck. I managed to get
> them sorta loose, but there must be something that can be put on them to
> make them turn more freely.  Any ideas? Tuning the 455 kHz IF strip
> improved things a bit.  Going on the higher bands, at 26.5 MHz, I was
> seeing -125 dBm at 1 kHz BW, and -123 dBm at 2 kHz bandwidth for a 10 dB
> S/N ratio. This is better than 0.3 uV.
>
> I listened on the BC band and with an 8 kHz filter, that carrier meter
> was always up near 100! It hardly ever moved. I had a good beverage
> antenna on it and could not believe the signal strength. So now I have
> an R-1051B, an R-390 and a 390A finished. The next step is to work on a
> couple of R-392s. When I get those running I have to choose which one I
> will keep as I don't have much room for all of them. What a quandary! I
> am leaning towards keeping the R-390 from the first Collins contract.
>
> Dave K1WHS
>
>
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