[R-390] Ballast Tubes

[Chuck Ochs]

One must keep in mind that the R-390 was a "general purpose" receiver, which
saw extensive shipboard use by the Navy during it's heyday. Power aboard
ships tends to be anything but stable. I know. I was a shipboard electrician
on an LST during that nasty little war back in the sixties. We had these
radios on board, as did nearly every other ship in the Navy at that time.
Using a ballast tube in the oscillator filament circuits was, at the time, a
clever way to maintain stability during all those periods where the line
voltage sagged from operating such heavy electrical loads as gun turrets.
The regulation of ships generators of the period was very slow by today's
standards. IMHO, there is little ( probably NO) need for this regulation
scheme given a radio running on modern "shore power".
A few years ago, the ballast on my VERY early R-390 died, and I simply
replaced it with a resistor. I did not notice any change in operation
whatsoever. It has been running this way for several years now.
Chuck N1LNH

----- Original Message ----- 
From: "Bob Camp" <ham at cq.nu>
To: "Forrest Myers" <femyers01 at bellsouth.net>
Cc: "r-390" <r-390 at mailman.qth.net>
Sent: Friday, July 02, 2004 7:24 PM
Subject: Re: [R-390] Ballast Tubes


> Hi
>
>  From what's been said here they are still available for something in
> the $30 to $60 range. Not quite a price that would encourage me to grab
> a couple dozen.
>
> One modification that has not been mentioned as part of this thread on
> ballast tubes is probably the oldest of the batch. Grab a plug that
> looks like a tube base and wire a resistor to it. The value needs to be
> right to get the filaments to run right but that's about all there is
> to it. It pulls no more power than the ballast tube and it's a totally
> reversible mod. When the bottom drops out of the ballast tube market
> you can plug one of those two dollar ballast tubes in there and nobody
> will ever know what you did.
>
> Somehow I doubt that ballast tubes will get cheap again unless there is
> a Chinese factory we know nothing about making them by the ton. They
> are not terribly high tech so it is a possibility. There may be a long
> forgotten warehouse in South East Asia with a few hundred thousand of
> them sitting on the shelves - stranger things have happened.
>
> If it was my radio I think I would do one of the re-wire mods to
> eliminate the beast. The filaments would be un-regulated but there
> would be less heat and no additional stuff inside the cabinet.
>
> The function of the ballast tube in the radio is questionable. With
> modern wall voltages the original ballast is running at best on the
> edge and at worst over the edge of it's ratings. It's not doing a real
> good job of stabilizing the filament voltages on a radio plugged into
> 120 to 125 VAC. Fortunately for all of us the filament voltage has a
> pretty small impact on the tubes in the radio. It's my belief that the
> problem comes in on the low voltage end of the equation. If you try a
> radio on 100 VAC then the ballast is probably a good idea.  Don't see
> much of that coming out of the wall outlets around here ....
>
> Take Care!
>
> Bob Camp
> KB8TQ
>
>
>
>
>
> On Jul 2, 2004, at 4:17 PM, Forrest Myers wrote:
>
> > Hello All,
> >  Came into the shack and found my r-390a dead. A quick check found the
> > ballast tube was shot. I've seen a lot going by on ballast tubes these
> > past
> > few days but am interested in getting a real ballast tube, if I can
> > afford
> > it, back into the radio.
> >  Anyone have a source for a 3TF7?
> >  If I must, I'll put in a mod to get around the 3TF7 but would rather
> > not.
> >
> > Thanks,
> > Forrest Myers
> > AG4ND
> >
> > -------------------------------------------------------------------
> > "Security is mostly a superstition.  It does not exist in nature...
> > Life is either a daring adventure or nothing."  -- Helen Keller
> > -------------------------------------------------------------------
> >
> >
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