1. That's suppressor (as Tauno noted), or even more accurately, beam forming
plates.
The transconductance to the suppressor is approximately zero. It's only of
significance when it comes to capacitance. (Which, obviously, is quite
important for GG operation at radio frequencies!)
2. I doubt you're going to get /anything/ of advantage out of either of
those tubes, by going GG. Even if the suppressor feedback weren't a burden.
That's the whole point of having a tetrode (or beam tetrode, or pentode)!
3. If you're operating at such high frequencies that you can't go with GK,
you're at the same frequencies where inductance screws you over. And these
sweeps don't even have multiple pin connections -- like most novar and
compactrons do (often, "undocumented" pins; find out by inspection). You're
barking up the wrong tree, forcing these tubes into this service. :-(
4. For tubes that should work higher, look for the short, late model sweeps
like 17GV5 and whatnot (B&W TV deflection). The electrode structure is
physically short, while the leads are the same length and size as any other
type; therefore the self-resonant frequency will be higher. Because, hey,
if you're trying to force >50MHz out of the poor things, every little bit
helps.
And they're cheaper, so you can use more of them, in parallel (or in any
other combination, if you like..), to get the same total plate dissipation.
5. As for actually burning up connections? Geez... As the other Tim W.
mentioned, CO2, umm, "ain't gonna cut it". You could maybe use a SS diode
laser in the near-IR or red spectrum (mind, the glass may be opaque in NIR
too), but you still have to solve for refraction due to the glass envelope,
which is a cylinder for one thing, but usually a bit wavy or lumpy besides.
Worst of all, vaporizing the connection will do two things:
a. Huge release of trapped gas. They bake them out during manufacture, but
I doubt they're 100% gas-free. They don't get them meltingly-hot. (Fair
point: if nickel does desorb fully at red or orange hot, then this won't be
a problem after all!)
b. That metal has to go somewhere. If you go carefully and melt it down,
you can get it to blob up, which will be better than vaporizing it outright.
Also, note that, in a vacuum, there's nothing to clear away melted gunk. It
won't magically *burn* a clean hole through the metal -- real laser cutters
use compressed air to blow away, and burn -- combust -- the heated material!
Probably, some evaporation will still occur, whether due to thin webs
getting superheated, or simple evaporation off the surface of the blobs.
(Checking, it seems nickel's vapor pressure, at the melting point, is
~fractional pascals, which is quite a lot higher than the pressure in a
normal vacuum tube. So it will evaporate noticeably.)
Any evaporated metal will deposit, well, pretty much anywhere it can,
line-of-sight. It'll go on the mica insulator (don't put the poor tube into
a TV receiver again!), it'll go on the envelope (maybe breaking it, because
that will absorb laser power?), it'll go on the grid and cathode (through
any holes nearby), contaminating them...
The surest way to proceed, would be to do it under maintained vacuum. Weld
an exhaust tube onto the glass nipple and pump it down. Ah, but at this
point, you might as well cut the whole thing open, go in there with diagonal
cutters and cut the damned thing by hand (sorry it's not as cool as Frikken
Lazers ;-) ), and seal it back up and re-pump (and re-getter--oh right,
you'll need to replace the getter too, and flash it later).
But at least if you're going to that trouble, you can put an actually-useful
base on it, like a compactron, and add more leads to the critical
electrodes.
Reworking a sweep tube... well... that'd be one hell of a *hack*, that's for
sure. :D
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Post by Phil HobbsPost by John CohenThe vacuum tubes are 26HU5 and 36LW6.
Both vacuum tubes have an internal connection between the cathode & screen.
I noticed Laser engravers on Ebay and the heads are sold separately.
I would like to use these tubes in Grounded Grid configuration.
Vacuum tubes operated in this manner the screen is grounded and the
cathode is excited.
Cannot do that with these tubes due to this visible from the outside of the tube
internal connection. The wire connection internally is very thin. Maybe a low
power Laser might just cut it.
Lasers are used to engrave metal. It seems one of these Laser heads might do it.
Any suggestions help appreciated.
Best John
I cross-posted this to sci.electronics.design because there are some old
time tube guys there.
Doing that with a laser will be difficult and dangerous for an amateur,
and then you still have the problem of how to ground the screen, which
would then be floating with no external connection, right?
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net