[R-390] My 'new' '67 EAC is now "on line" 8^) Ballast Tube question.

[Barry Hauser]

Phil wrote:

>Well, it looks like all the trials and tribulations associated with this
PTO
>are over.

That's good news!  Now that your skill-sets are at their peak, let's
everybody send Phil a Cosmos to fix 'n tweak.

>The receiver alignment went very well,

By now the radio probably feels bad about running you through the ringer, so
went easy on 'ya.

>..a new 3 wire power cord
> has been installed and the unit placed in its CV-979 cabinet.   The
>alignment was already very close and just needed a light tweaking.  A
modest
>improvement in gain was noted when some of the Xtal oscillator trimmers
were
>adjusted.

>Only one minor glitch was noted during alignment.  The 28 MHz band was
dead,
>removing its Xtal and tightening up the pins of the socket cleared that
>problem.  Whew, thought I had a bad Xtal at first.

I've found the same thing as well as some bad xtals here and there.  The
crystal sockets vary, but not the greatest in the later receivers.  Probably
the stamped cupped type. Not much contact area and metal is none too
springy.  Fix is easy.  You probably just staked them down a bit.  Was it
just the 28 MC band?  Is that the one solo crystal -- usually two or three
bands are involved.  Anyway its fixed.  They tend to loosen up when the
radios are moved or shipped and the crystals actually wobble in those
holders.  Further compromised as a tiny bit of oxidation will cut them out.

<snipped>
>BALLAST TUBE QUESTION:  In all the R-390A's that I've had previously (that
>still had the ballast tube) I seem to recall the filament having just a
dull
>glow in only a small part of the filament.  This one glows fairly brightly
>over nearly the entire length of the filament and makes me feel uneasy in
>that I'm afraid it's nearing the end of its lifespan (seems I recall
reading
>that was an indicator).  No, my line Voltage is under 120 VAC, especially
>this time of day with everybodies A/C running.  Do I have cause for
concern?
>Perhaps I should start looking for a 12BH7 tube (I did the 12BH7 mod
>while recapping the IF strip).

My experience is that they don't glow much after power-up.  The ballast may
be good but you may have excessive current draw.  Since you replaced nearly
everything else that could affect that, I strongly suggest you check the two
tubes involved -- especially the one in the PTO.  Yes -- lightning
(element/filament shorting) does strike twice, (Phil found the previous PTO
tube shorted).  Two possible reasons,  offhand -- continued bumping/moving
of the PTO as you were adjusting the linearity and/or the replacement tube
may have come from the same lot with a latent defect.

Now that things are settled in, test those tubes again in the tester.
Normally it's not best practice to leave them in the tester too long, but
let them sit and tap as you go through the shorts test.  Another
possibility -- something in the wiring harness.  Maybe you should measure
the current draw with the ballast in place.

Do others agree about the bright ballast situation?

Barry