[R-390] Ballast Tubes in Shipment

[Barry Hauser]

Hi James

Yes ... there have been reports of that happening from time to time and when
I've had '390's shipped to me, I've asked that the 3TF7 be removed,
bubblewrapped and stuffed in somewhere.  Way, way back, someone posted that
their ballast tubes would seem to last forever, but a failure, when it
occurred, tended to be after the receiver was moved around -- onto the bench
or whatever.  Others have sort of dismissed all that.

What's curious is that the last model series of the Zenith Tranoceanic tube
portables (600 series) and the military version of the 500 series (R-520)
all have 50A1 ballast tubes.  The construction of the tube is the same -- a
9-pin envelope with a long iron filament strung around almost "nonchalantly"
over the mica disks, like a poorly decorated Christmas tree.  These are
portable, luggage style radios with no shockmounting whatsoever.  There were
numerous clones and also mil portable gear with ballasts -- and some tube
testers.   So -- I dunno.  If they were prone to vibration damage, would the
mfr's go with them in portable gear?  Not sure, but I doubt ballast tubes
were ever cheap relatively.  Nowadays, it's a horse race as to which would
cost you more -- a 50A1 vs 3TF7.  Of course, those T/O's also have the very
pricey 1L6.

As for vibration/shock hot vs. cold -- the T/O's are battery portables, so
might very well be in motion while running -- and included the famous
removable "wavemagnet" with suction cups so you could attach it to the train
or car window while traveling.

I suspect failure-proneness may have to do with aging through use -- 
filament becomes more brittle with more heating and cooling cycles?

Barry


----- Original Message ----- 
From: "JamesMiller" <jmiller1706 at cfl.rr.com>
To: <r-390 at mailman.qth.net>
Sent: Saturday, July 03, 2004 9:48 PM
Subject: [R-390] Ballast Tubes in Shipment


> One or two 390a's I have bought in the past arrived with bad ballast
tubes.
> But they were presumably working before shipment.  The only reason I can
> think of is excessive vibration and breakage of the flimsy filament during
> shipment.    Solution?  Before shipping a 390, remove the ballast tube and
> wrap in soft foam and in a separate box inside the shipping carton.
>
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