[R-390] R390 Restoration

[Chuck Rippel]

I restored my Collins R390 over the long weekend.  I had it traded to me on a 
"it worked the last time I tried it" basis.  Basically, that means it was broken 
and the "seller" pretty much knew it. 

Very, very oblique problem.  It would develop a 60 cycle hum as soon as a 
station was tuned in and superimpose that over the received audio.  Tune 
away, it would "sound" fine.   Although I have never operated one let alone 
repaired an R390, knowing the power supplies in those things are the source 
of 70% of the problems and basically cook themselves due to the heat 
generated by the 6082 regulator tubes, I went there first.

As soon as I got the power supply removed, I knew I was in the right 
neighborhood.  There was plenty of nip and tuck work that had been done 
under the regulator module including some modifications.  No cooked parts or 
wiring.  The 47 ohm (?) resistors looked like new.  Noted the hum balance pot 
so knew the supply had to be balanced out.  Replaced some out of spec 
resistors but found the real problem to be a 100pf mica cap from one of the 
6082's to ground that turned into about a 900K resistor.  I will have to come 
up with some solution to the heat generated by that module though.  A CPU 
fan over one of the holes in the side might go far to help.

My guess is that the leaking capacitor was pulling on the supply just hard 
enough that when a station was tuned in and the power supply subjected to  
further load, would add enough additional stress to overload the supply just 
enough to make not regulate and hum.  That's my theory, anyway.

Its not a full restoration but was about 80% of what I imagine one would entail. 
Didn't pull the gear train and put it in carburator cleaner as I normally would 
and looking back, it really should be done.  I have heard of a green gear that if 
you pull or move, thats pretty much it.  I didn't see it and decided to leave that 
phase alone.  Left the gears in the RF deck and scrubbed them down with a 
long bristle brush, a toothbrush and carburator cleaner.  Got probably 70% of 
the old grease out, rinsed the carb cleaner out and followed that with a 
scrubbing with 50/50 Simple Green and water solution then a thorough rinse 
with hot water.  Blew out the gear train with compressed air and let it sit in 
the 100 degree heat we had one day.  Once dry, I re-lubricated everything, of 
course. 

Pulled each slug rack out and dipped the bearing in the carb cleaner and gave 
them a twist.  Cleaned everything but the actual slug with a toothbrush then 
submerged the bearing ends a final time and moved them.  Gunk came out 
and the bearings on the racks move nicely now.   Lubed the bearings and 
faces of the racks with 90W oil and placed them back in the radio.

No wholesale replacement of capacitors in the IF deck but noted there are  
certainly plenty of them.  I imagine they could give you a fit if one started 
leaking.

Anyone out there in List Land have information on which ones commonly fail 
in this radio?  Other common problems that I ought to chase down before 
they become serious issues?

Found the 1st RF tube replaced with a 6AK5 v/s a 6AJ5 as are all the 
oscillator tubes.  Also, there is a 6BH6 as the last IF amp.   I wonder if these 
are helpful mods AKA: W3HM and the 75A-4 mods or did someone popped 
some tubes and just stuck those in 'cause they fit?

Repainted and re-lettered the front panel.  Stripped and painted the knobs, 
cleaned all the sub-chassis, set the PTO length, balanced the upper and 
lower band end over-run and set up the mechanical alignment for the cams.  
Tied it all together by setting up the Cam Position/PTO length/electrical 
relationships, centered the Antenna Trimmer and then did a full IF and RF 
alignment.

To put it bluntly, the radios performance is impressive.  I did not do a full 
sensitivity test but knew it was very hot.  For some reason, I had it tuned to 
15.400 and heard Radio Kuwait with no antenna connected other than the 
shielded BNC cable going to the HP-8640B generator.  I did a spot check at 
the 3.8 mhz RF deck alignment point and was floored.

Ben Wallace and Mike Harris (just finished his) are currently tied for "most 
sensitive R390A's I have yet to restore."  This one beats both by a hair but, 
keep in mind, its a different radio.  Much higher build quality in the non "A" 
but I am not sure there are performance differences between the non "A" and 
the "A" that would justify what must have been the cost difference.

I'd like to find out the various problem caps and maybe pre-emptively replace 
them.  Also, the filter caps seem to be either papers a-la the 32V-3 HV cap or 
are oil filled's.  They could also probably stand to be replaced, again on a pre-
emptive basis.

This does not make me an R390 expert and I have no plans at present to 
start restoring them.  Having no real parts stock and little direct experience 
makes that idea one who's time has not yet come.  However, its a start.

-73-


-----------------------------
Chuck Rippel, WA4HHG
R390A List Co-Administrator
Reply to: R390A@R390A.com

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1968 Contract Dittmore-Friemuth R390A #38
1967 Contract EAC R390A #2808 with outboard Sherwood SE-3 Sync. Detector
1967 Contract EAC R390A #5295
1967 Contract EAC R390A #5591
1967 Contract EAC R390A #1023

All in regular use as premier Shortwave Broadcast DX Receivers
       -and-
Vintage AM Amateur use
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