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

[Steve Toth]

DaveCongratulations on getting the R390A up and running!
Personally i would like to know how you found the bad bypass cap.  I have a "blue striper" R390A sitting in the closet that I have to eventually get to.
And, IIRC, you can use small amounts of talcum powder to lube the tuning slugs.  Check the R390A info page and Wei Lee's "Pearls" to verify that - I'm reaching way back in the gray cells here.
P.S.  I've always been tempted by the R392 - they are so funky they are absolutely cool!  But then I would have to buy an old military truck/command car/jeep (personally I like old Dodge Power Wagons) to put it in.  I have no problem going down that rabbit hole, but the wife..............;-).

- Steve  W7SJT

"Always look for a positive solution then Improvise, Adapt, and Overcome"

- adaptation of the U.S. Marine Corps motto




"Every day is an opportunity to challenge the achievement of your dreams"




"Success is not final, failure is not fatal.  It is the courage to continue that counts."

- Winston Churchill










 
 

    On Saturday, November 30, 2019, 06:43:03 AM MST, 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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