[GreenKeys] [External] off topic - vacuum tube lamp

[Jones, Douglas W]

From: Nick [creativegardening at hotmail.com] -- Tuesday, April 5, 2022 1:21 PM

> I acquired this tub a few years ago online from a Russian seller. It is a GM-100 triode tube, the biggest one ever built. 

The overall dimensions look similar to the Eimac 750TL, which also measures 18 inches tall but has a spherical body and a grid cap sticking diagonally out the side.  I had one, see this photo:
-- https://commons.wikimedia.org/wiki/Category:Eimac_vacuum_tubes#/media/File:JAN-750TL-tube.jpg

I ended up donating it to the U of Iowa Physics Department, which has a small museum of such stuff.

One noteworthy feature is that, in use, the plate would typically be red hot, heated in part by the filament, but moreso by the electrons slamming into it.  The Eimac 750 was rated at 750 watts DC power, 1KW RF.  Applications in the data sheet included running DC servomotors and running stadium PA systems.

I have seen a power triode that was close to a yard (meter) long, so your tube and the one I had are hardly the largest ever made.  My father used to have one in his office with a plate cap that was perhaps 18 inches long and 4 inches in diameter.  The plate cap was the plate electrode, with the filament and grid cantelevered from the base to hang inside the plate.  The cap was designed to be water cooled, so you'd clamp the cooling coils to the plate to make both electrical and thermal contact with the plate.  The body was a thick glass globe with a short stubby grid cap poking out the side and pins on the base for the filament power.  That tube is now in the departmental collection of the U of Michigan physics department.  It used to power a cyclotron back in the 1950s.

Here's a modern datasheet for a 20 KW tube.
-- https://s1.manualzz.com/store/data/014170404_1-19303e27fee3cc4f35e343c26e397d5d.png
I love the fact that the filament power on this tube is 750 watts.  Like other water cooled tubes, of course, it would make a lousy lamp, since the filament is inside the solid metal plate assembly, and in this and other modern examples, the insulating parts are all opaque ceramic.

          Doug Jones
          jones at cs.uiowa.edu