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Tube of the Week




 
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December 01, 2022, 07:32:42 PM *
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Patrick J. / KD5OEI
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« Reply #75 on: November 03, 2022, 01:07:09 AM »

How about the 2D21? Not much is said about these little Tetrode Thyratron control tubes, and I learned something new about them today.

The 2D21 has alternate numbers such as the 4G/280K from STC, CV797, and its rugged versions, the 5727 a.k.a 2D21W sporting a 720G maximum shock rating. Some uses are relay control and radar pulse modulators. They work well on 120VAC circuits.

HTR=6.3V/600mA
peak inverse voltage = 1300
forward voltage  = 650
peak current = 500mA
average current = 100mA
surge 0.1 second = 10A
ionization time = 0.5us
plate voltage drop = 8V

The interesting thing comes from a old book "Gas Discharge Tubes" - it's from the internet and I don't know who wrote it, but they included a cut-away view from Penta Labs.

Looking at a physical 2D21, you see the grey anode - but it's an enclosure, not the anode. The anode is inside it. (page 67, figure 40)
The second grid is not a screen grid, but G2 is called the shield grid. It runs at -10 to -100V relative to the cathode.
The internal elements are fairly rugged, with G1 being the main example.

The 2D21 remains available in large quantities for low cost and could be considered an electically rugged alternative to some solid state switches.









* 2D21 cutaway view.png (97.21 KB, 810x1028 - viewed 32 times.)
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« Reply #76 on: November 03, 2022, 08:15:55 AM »

Hi Patrick,

   I once witnessed a 2D21 save a mans life!

Back in 1981 I took a job at the former Accelerators, Inc in Austin Texas. They had become a division of Veeco, and existed till 1987.

The chief Physicist, Joe Cecil, W5RIQ (SK) had an ion beam test stand that would accelerate an ion beam up to 120 Kev (ev = electron volts).

One day, there was Joe standing there with his arms outstretched on the beamline, and I witnessed a series of arcs, about 2 per second striking his hand.

It happened so fast, and before I could take action, the arcing stopped, and Joe lowered his arms, and without expression, he walked away! He was as white as a ghost!

He later explained to me, that the big 0-150KV Hippotronics supply had an arc fault circuit where it would shut down the supply after a fixed number of arcs.

The control element in that circuit was a 2D21!!

Jim
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« Reply #77 on: November 03, 2022, 08:47:22 AM »

"ENCLOSED ANODE TUBE SAVES LIFE!"   Great story and whatta strong tube!  TNX Steve
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w4bfs
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« Reply #78 on: November 04, 2022, 10:02:38 PM »

I remember some early West Coast handbook circuits where a 2D21 was used as a 9 Volt regulator.  Filament voltage may not have been used, sorry just can't remember.
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« Reply #79 on: November 06, 2022, 06:36:33 PM »

Talk about safety circuits! It's even more interesting a tube after reading that.

The regulator circuit is in the 14th, 15th, and 16th ed. It's started through a high-R resistor to low B+ supply and serves as series-connected cathode bias for the 811s, instead of the Zener diode which did not exist at the time.
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