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

[Barry Hauser]

Well, Phil, you may have another project on your hands .... time to
re-string and recharge that ballast tube.

There are several ways of cutting the glass open, but making all those tight
curlycues in the iron wire is tough.  Then you have to carefully drape it
over the insulators and spot weld the ends to the pins.  Use a torch to
re-fuse the envelope back together, open the nib, apply vacuum then quickly
infuse the hydtrogen and seal it with a torch somehow -- without exploding
the hydrogen.  Then check DC resistance, and if it's too far off, start over
again.

Yessss -- I'm joking.  Just an extended application of the Cosmos rehab
thing.

Anybody know:

1.  Is the performance degraded when the ballast tube starts to glow
brighter or show hot/thin spots?
2.  How long before total failure?

It would seem unwise to invest in used 3TF7's, unless observed in operation.
Someone (Hank?) is offering NOS 3TF7's at a (relatively) reasonable price,
so you might want to have one in reserve.  If you don't want to make that
investment, I'd suggest the power resistor option -- have one handy as you
can just stuff the leads into the tube socket at a moment's notice.  If you
subsequently want to convert to 12 volt tubes or whatever, you're not
tossing anything expensive.

(I know once you get into DXing and monitoring mode, you don't want to be
down long -- even though you have that VR-5000 as backup.)

Barry



----- Original Message -----
From: "Phil Atchley" <k06bb@elite.net>
To: "'rbethman'" <rbethman@comcast.net>; <r-390@mailman.qth.net>
Sent: Wednesday, July 16, 2003 3:31 PM
Subject: RE: [R-390] My 'new' '67 EAC is now "on line" 8^) Ballast Tube
question.


> Well, to reassure myself and others who have expressed concern I borrowed
> some tubes from another receiver here (my homebrewed longwave beacon set)
> and subbed both the PTO and BFO tubes at the same time (and yes, they are
> 6BA6's, not 3BA6's 8^).  No change, the ballast glows the same.  I've just
> come to the conclusion that this one may be drawing close to the end of
its
> lifespan.  I can't find it in my archives, but I KNOW I read somewhere in
> the past that is an indicator that either the ballast tube filament is
> getting "thin" (worn out) OR that possibly the inert gas has leaked out of
> it around the seals.
>
> I also tightened up the ground screws on the applicable tubes, though I
> would suspect that a loose one would open up the filament line or at least
> present a high impedance that would actually REDUCE current rather than
> increase it.
>
> 73 de Phil, KO6BB
> DX begins at the noise floor!
> k06bb@elite.net
> Merced, California
> 37.18N  120.29W  CM97sh
>
> -----Original Message-----
>
> Phil,
>
>     Experience has shown that the filament of the ballast tube SHOULD
> only partly glow when all is well.  The symptoms you describe SHOULD
> mean that the circuit that it regulates is drawing too much current.
> Either one of the tubes has some form of a short, or something else is
> causing excessive current draw.
>
>     It's probably going to be painful to track down, but will be worth
> it in the long run.  As mentioned in an earlier post, if the PTO tube
> came from the same lot, it could be a bad lot.
>
>     Try swapping the two tubes that R510 regulates from another R-390A.
> If the ballast tube goes down in brightness, then one or both of them
> are problem children.  IF NOT, then something else is awry.  Perhaps a
> bad or flaky ground.  These radios are notorious for this with the MFP
> coating
>
>
>
>
>
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