[R-390] They followed me home <GRIN>.

[DCrespy@aol.com]

Phil, a few notes (I hope will supplement Barry's good advice):
> 
> QUESTION 1: Seeing as how these units have the rectifier tubes in place,
> how high do I need to bring the Variac before they will start conducting
> enough to start forming the caps, at least some?


You can reform the caps outside the unit.  I think this is easier, especially 
for the plug in caps found in mil receivers.  Let the cap charge through a 10 
to 30 K , 5+ watt resistor, connected to a 200 to 300 volt DC source.  If you 
watch the voltage across the cap.  It will rise very slowly as the cap 
reforms.  Leave it on this rig for an hour or so.  Then discharge it, plug it 
in and fire up the rig.  BE VERY CAREFUL, A CHARGED CAP IS VERY DANGEROUS 
(experience based advice!).

> QUESTION 2:  One unit has what appears to be a Collins PTO, the other a
> Cosmos unit.  Assuming they both work well, which one should I put in "my
> keeper"?

Cosmos can be externally adjusted for linearity.  Collins requires a special 
fixture to set up the "corrector stack".  I'd go with the Cosmos, long term.

> 
> I intend to run both units up and give them a thorough checkout before
> doing a complete re-cap.  They were supposed to both be playing when put
> in storage two years ago, though he said both had problems on certain
> bands.
> 

Regarding recapping.  If the radios used Black Beauty plastic encased caps or 
their Brown equivalents, then I'd go ahead an replace them.  I find some of 
them cracked allowing mosture to screw up the paper dielectric.  If they are 
the metal and glass versions, I've had yet to find a bad one.  Frankly, in 
either case, in my R-388 / R-390A (and other Collins) restorations I have had 
more trouble with defective postage stamp micas, than with the 
coupling/bypass caps most folks replace.  Look for bad mica caps anywhere 
they are in the B+ line (in plate circuits).

Regarding trouble with certain bands, you got some great advice from Barry on 
this.  Check the band crystals, their connections and their trimmers.  Also, 
if the problem is all bands below 8mHz, it is the crystal oscillator on the 
RF deck.



Good luck and 73 
Harry  KG5LO


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