[R-390] Waking up my non-A

[David C. Hallam]

In spite of all that has been written in various reflectors, etc. and
conventional wisdom aside, it is not a good idea to "bring up slowly with a
variac" a vacuum tube radio.  Vacuum tubes will not conduct until the
filament temperature reaches design temperature (or close to it).  Nothing
good can come from letting the tubes try to operate at a low line voltage
for any extended period of time.

If you want to reform electrolytics in place, risking your power transformer
in the process, you can remove all of the tubes and replace the rectifier
tubes with ss diodes.  Then raise the voltage slowly with a variac.
Fortunately the R-390 doesn't use an electrolytic in the power supply.

David
KC2JD

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of John Lawson
Sent: Friday, January 06, 2006 5:37 PM
To: R-390 at mailman.qth.net
Subject: [R-390] Waking up my non-A



  Some months ago, thanks to a botched listing header, I found (and was the
only bidder on) a 390 (non-A).

  It is a Motorola, sn 3585, MWOs 11-5280-294-35/1 and /2.
  It has a Collins PTO.

   Been modded a bit, mostly in the audio output wiring.

   I brought it up slow on a variac and ammeter - after a couple of hours
'soaking' at 60V on standby.

   After working up to full line voltage, and nothing
exploding/burning/complaining, I am now in a position to make 'er Work.

   So far - it's 50/50.  Overall operation is quite poor - but it is
working a little.  There is backround noise, controllable by the RF gain,
the BFO is working, and there appears to be recievable Calibrator signals
(every 100Khtz) above 19 or 20 Mhtz.  There is a birdie at 250kHtz and 710
kHtz on all bands.  So far the only band that seems to be paying attention
to the Outside World is 21 mHtz - faint sigs can be heard that respond to
the controls, and stop when the antenna is removed - I'm using the Unbal
ant for this quick-and-dirty test.

   Mechanically, aside from being in desperate need of Oily TLC, it seems
to be all there and working - nothing's binding, no coupler parts on the
bench, no stuck/broken slugs.  Even has the small green stamped gear
affixed to the front of the IF rack, with "MWO" stamped next to it.


   I have the Manual on CDROM, which I need to get immersed in, but I
thought to ask the Gurus and Pundits if there is a 'condensed' set of
tests or procedures I might undertake in the meantime, to narrow this down
a bit?

   I'm sending my R-388 panel off for re-furb while I fix it's PTO and give
it new tubes and a few new capacitors, so I was hoping to use the R-390 as
'companion' radio to the -390A I have as my main receiver.

  Cheers

John  KB6SCO


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