[R-390] Re: IERC tube shields and tube temps...a field expedient...
Bob Camp
[email protected]
Tue, 22 Apr 2003 22:20:23 -0400
Hi,
Even with an indirectly heated cathode the contact between the filament and
the cathode is very good. The insulation (vacuum) around it is also really
good. The result is that the cathode gets to the filament temperature and
isn't affected very much by what's around it. The self regulation of the
filament still keeps things going at a constant temperature. Given that then
tube shields aren't going to have much of an affect.
The getter (hopefully ....) stays nice and cold through the process. By that
I mean that you don't want it to melt or worse yet vaporize. Generally you
pick getter material so that this is not going to happen in any reasonable
combination of conditions. As long as you stay below melting temperature
it's hard to say exactly what the getter will do as a function of
temperature. It's affinity for crud goes up as temperature increases, but so
does the tendency of the crud to turn back into a gas. Is it better hotter
or colder ? - depends on the material and what you are trying to "get". You
hope the guy who made the tube knew his stuff. If he did have a choice then
I'd guess he optimized for a bare tube with no shield.
Take Care!
Bob Camp
----- Original Message -----
From: "menges" <[email protected]>
To: "Bob Camp" <[email protected]>
Sent: Wednesday, April 23, 2003 12:22 AM
Subject: Re: [R-390] Re: IERC tube shields and tube temps...a field
expedient...
> Directly heated element/Filament. How about the indirectly heated
element.
> How about the getter??
> Al
> ----- Original Message -----
> From: "Bob Camp" <[email protected]>
> To: "Darryl Jones" <[email protected]>; "Kenneth G. Gordon"
> <[email protected]>; "R-390 List" <[email protected]>
> Sent: Tuesday, April 22, 2003 6:01 PM
> Subject: Re: [R-390] Re: IERC tube shields and tube temps...a field
> expedient...
>
>
> > Hi,
> >
> > Enormous chunk of wasted bandwidth follows ..... 1200 baud modem users
> > proceed at your own risk :)
> >
> > This gets a little complex. On the thermometer question it depends on
what
> > you want to measure. An IR thermometer will measure the temperature of
the
> > inside of the tube IF the glass used is transparent at IR AND you know
the
> > emisitivity of the thing you are pointing at. Since the thermometer
> responds
> > to light you have to know how much gets through the glass and "what
color"
> > the thing you are looking at is. You can check both things out, you just
> > have to break a couple of tubes to do it. If you want to measure the
pin
> to
> > glass seal temperature then you need a nice little thermocouple.
> >
> > Now for the complex part. Tubes wear out for a bunch of reasons:
> >
> > 1) Filaments go open circuit
> > 2) Gas
> > 3) Filaments loose emission
> > 4) A grid goes open or short.
> >
> > In receiving tubes (rather than rectifiers or power amp tubes) filament
> > emission is not usually a big deal. The tube will work pretty well even
> with
> > a well worn filament.
> >
> > Gas can come from the stuff inside the tube, but in modern (post WWII)
> tubes
> > usually if it's gassy it's because it leaked.
> >
> > Grid open and shorts usually are from shock and vibration.
> >
> > Filament open's are a function of how often the tube is turned on, and
> > exactly how power is applied. A fast power on *may* actually be better
for
> > some tubes than a slow power on.
> >
> > Still with us .....
> >
> > High temperature affects outgassing from stuff in the tube, and leaks in
> the
> > glass to metal seal. Unless it is combined with shock and vibration it
> > should not affect grid problems. This assumes the grid is not glowing
> orange
> > ....
> >
> > Filament opens and cathode emission don't seem to correlate well with a
> > modest change in the tube temperature. The filament is running in a
> fashion
> > that it self regulates it's temperature. Once it is at temperature it
will
> > run there for a good long time. Again provided that there is little or
no
> > shock and vibration.
> >
> > All the yack above about filaments assumes that you run them to the same
> > voltage each time *AND* that it is roughly what it should be. The
filament
> > has a bit of a memory affect so varying the filament voltage all over
the
> > place does some weird things.
> >
> > Finally the tube shields (at last ...)
> >
> > Tube shields will affect the temperature of the upper glass bulb and of
> the
> > plate. Indirectly the grids may be cooled a little. The temperature at
the
> > glass to metal seals may not change much at all with black versus shiny
> > shields. A full contact shield might reduce the temperature a bit, but
it
> > could also raise it a little. Air flow would have an affect on the
outcome
> > here.
> >
> > But what about the data you ask ....
> >
> > Yup the data is out there and it's correct. The tube shields do have an
> > affect on the life of the tubes in an R-390. Good Navy data and no
reason
> to
> > doubt it. A couple of questions:
> >
> > 1) Does you radio see as much shock and vibration as the shipboard
radios
> > the Navy ran the tests on?
> >
> > 2) Did they toss the tubes when they failed on a tube tester or failed
in
> > the radio?
> >
> > 3) Do the tubes you use fail at the rate that the Navy tubes did?
> >
> > 4) Did the radios have tube or solid state rectifiers?
> >
> > The last question is the most interesting. Even in 24/7 type service I
> don't
> > see anything close to the Navy failure numbers. I also do not run tube
> > rectifiers so maybe all their failures were rectifier tubes.
> >
> > What's more to the point, back in the 1980's your government and mine
went
> > out and bought tubes for "essential equipment" to keep it running for
> > something like another 20 years. The good old R-390(both A and not A)
> *must*
> > have been on the list. The mountains of tubes we see on eBay are a
result
> of
> > them surplussing these tubes. You can find all the tubes except two -
the
> > ballast tube and the rectifiers. I can understand the ballast tube, it's
a
> > different category and probably didn't get covered in the order to buy
the
> > vacuum tubes. The rectifier may have been left off since the solid state
> > conversion was an approved modification. If that's the case then they
> didn't
> > go through anything close to the number of tubes they thought they
would.
> I
> > suspect that most of us on the list have more than ten sets of spares.
> Heck
> > I'm probably not that odd in having a couple hundred of some of them.
Hall
> > of fame land may be in the multiple hundred sets range. We're all out
> > grabbing these tubes and they are still dirt cheap. There have to be an
> > ocean of them out there. We don't run as many radios as the Navy did,
but
> > then they didn't plan on a 500 year supply of tubes either.
> >
> > Bottom line - fancy tube shields are neat and they do look slick. For a
> > truly presentation grade radio they are the only way to go. If you put a
> > couple hundred bucks into the front panel then they are cheap by
> comparison.
> > For a use it every day and I don't care what it looks like radio, save
> your
> > money ....
> >
> >
> >
> > Take Care
> >
> > Bob Camp
> > KB8TQ
> >
> >
> >
> > ----- Original Message -----
> > From: "Darryl Jones" <[email protected]>
> > To: "Kenneth G. Gordon" <[email protected]>; "R-390 List"
> > <[email protected]>
> > Sent: Monday, April 21, 2003 7:18 PM
> > Subject: Re: [R-390] Re: IERC tube shields and tube temps...a field
> > expedient...
> >
> >
> > > Well, I'm gonna give it a try and find out. Whats the worst that
> > > can happen? I lose a couple of tubes, of which with one or two
> > > exceptions, I have bucketloads :)
> > >
> > > Does anyone have a suggestion of how I can measure tube temps
> > > accurately?
> > >
> > > Darryl
> > > ----- Original Message -----
> > > From: "Kenneth G. Gordon" <[email protected]>
> > > To: <[email protected]>
> > > Sent: Monday, April 21, 2003 1:28 PM
> > > Subject: [R-390] Re: IERC tube shields and tube temps...a field
> > expedient...
> > >
> > >
> > > > I have had pretty good luck with simply spray painting the
> > > > inside and outside of a shiny tube shield with flat black paint
> > > > after masking off the lower part which would make electrical
> > > > contact with the grounding ring on the socket. My idea was that
> > > > the shiny interior of the tube shield was reflecting some of the
> > > > heat back into the tube, and by painting it black, some of that
> > > > reflected heat was absorbed instead by the shield and
> > > > transferred to the outside.
> > > >
> > > > Temperatures were noticeably lower for tubes with which I
> > > > tried this, although I didn't actually measure them.
> > > >
> > > > I have not yet tried to cut ventilation slots in them.
> > > >
> > > > I suppose I should try some sort of heatsink material around the
> > > > outside where it might fit.
> > > >
> > > > Ken W7EKB
> > > > _______________________________________________
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> > > > [email protected]
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> > >
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> > >
> > >
> > >
> >
> >
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