[R-390] starting 390A restoration

[nryan at mchsi.com]

Hi, Ed,

It's all true what you say about the Motorola corrector stack.  One should avoid messing with it.  In my limited experience with them, I've found them to be within spec.  I think I read somewhere that a special jig was used in their manufacture and the factory's girls found it to be the most difficult part of assembling Motorola PTOs.

I should have made clear the reason for sending the PTO link was to give one a feel for what's inside a PTO.  If I remember right, the Motorola end point coil (where one might have to take off a turn) is similar, though not identical, to the Cosmos but the pics give an idea of what's inside.  They should help one decide if the work is too daunting to undertake.

While working on the PTO, it's a good idea to disconnect its heater wires so as to avoid the bad effects from inadvertently leaving the ovens switch on.  The PTO's thermostat can stick and the resulting overheating can totally cook the innards.  If the shack is comfortable for humans, ovens should be switched off in any case as they likely are intended for extreme climate conditions such as inside an unheated shelter or where maximum operational stability is required, say, for RTTY gear.

Use extreme care tearing down and reassembling an RF deck geartrain.  Take photos and make detailed sketches as you go.  Having another working geartrain handy is helpful.  I have found, despite my best efforts, that even my pics and sketches may have omitted something and have had to look at the working unit.

If you take extra pains, the geartrain should turn silky smooth.  Gently debur the split gear faces.  Load gear springs lightly, just sufficiently to eliminate backlash.  Lube lightly with Mobil One synthetic oil.

Both those links are worth clicking onto as their content is very well written and profusely illustrated.

Have fun!

73 de Norman

Any activity becomes creative when the doer cares about doing it right, or doing it better. -- John Updike


----- Original Message -----
From: djed1 at aol.com
To: nryan at mchsi.com, bobyoung53 at hotmail.com
Cc: r-390 at mailman.qth.net
Sent: Sat, 1 Dec 2012 15:06:33 -0600 (CST)
Subject: Re: [R-390] starting 390A restoration


 Good advice on replacing the black/brown beauties, but don't rely too much on the PTO article.  The linearity adjustment on the Collins/Motorola is substantially different than on the Cosmos.  My advice is to leave the linearity alone- adjust the endpoint and take a turn off if needed, but I don't recommend trying to adjust the corrector stack.  It usually is pretty good after you get the endpoint correct.
I've recapped mine, but I chickened out on disassembling the gear train.  I just flushed it with cleaner and relubed.  But mine wasn't real dirty to start with.
Ed  W2EMN


-----Original Message-----
From: nryan <nryan at mchsi.com>
To: Bob Young <bobyoung53 at hotmail.com>
Cc: r-390 <r-390 at mailman.qth.net>
Sent: Sat, Dec 1, 2012 2:40 pm
Subject: Re: [R-390] starting 390A restoration

Hi, Bob,

You're referring to the IF deck, not the RF deck, right?  The IF deck contains 
the "death cap."

You should replace any brown or black plastic-encased tubular caps, but keep the 
metal-encased ones except the "death cap."  That cap should be a high quality 
orange drop rated at 600VDC.

Replace out of spec resistors to optimize the unit and thus gain peace of mind.  
I use original carbon comp type resistors.

Here's a link to helpful photos of a geartrain teardown from a fellow (I think) 
r-390 list member:
http://militaryradio.com/R390A/R390RFDeck/

Your PTO make is Motorola, but this link to a Cosmos PTO rebuild may be helpful:
http://r-390.com/cosmos.htm

Good luck,
Norman

Any activity becomes creative when the doer cares about doing it right, or doing 
it better. -- John Updike


----- Original Message -----
From: Bob Young <bobyoung53 at hotmail.com>
To: r-390 at mailman.qth.net
Sent: Sat, 1 Dec 2012 12:42:50 -0600 (CST)
Subject: [R-390] starting 390A restoration


I have a Motorola R-390A I bought some years ago and have finally decided to 
start to restore it. It will be my first 390A rebuild. Everything worked last 
time I powered it up but it needs mucho maintenance. I plan on taking apart the 
gear train, lube it adjust it etc with the help of the Y2K manual (which looks 
really well done by the way), also see if the PTO (Motorola) can be brought back 
to within specs without taking a turn off (doubt it, it's more than 10 Kc off 
end to end), recap it, align it and do anything else that needs to be done. I am 
reading (and reading) the R-390A Frequently Asked Questions Page but am sure 
I'll have a lot of questions. The first is I pulled the RF deck today to see if 
it had the death cap still in it and it does. I also noticed three or four brown 
beauties in there, probably a stupid question but should I replace those also? 
Resistor checks also? Thanks,

Bob Young
KB1OKL
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