Specs for the Thyratron

The 2 inch tube that made the work in possible was the miniature thyratron conceived by Joe Desch and achieved in the lab in Bldg. 10 before the war. Below are the specs submitted by him when he let the contract to Sylvania for manufacture. More information can be found in the second session of the interview with Joe Desch and Bob Mumma for the Smithsonian. Below is an excerpt from Bob Mumma:

[Page 75]
RM: Well, of course, one thing happened. By the time we went into the war for the Navy, we got a – we had Sylvania build tubes to our specifications .. that were these miniature thyratrons, and they were the 2C4 and the 6D4. By the time we went into the war for the Navy, we got a – we had Sylvania build tubes to our specifications.

or more information on the 6D4, see the National Valve Museum and the Radio Museum. The 2C4 is more elusive but I did find the specs at the site of Roy Tellason.


Fast Firing  Miniature Thyratron

Fast Firing Miniature Thyratron

October 19, 1942

Officer in Charge

Naval Ordnance Laboratory

Washington Naval Yard

Washington, D. C.

Attention: Mr. L. R. O’Neill

Dear Sir:

In accordance with the request of your Mr. R. C. Green by long distance telephone on Saturday, October 17, 1942, we are shipping tomorrow by parcel post, four miniature thyratrons developed by the NCR Company for special research use and four miniature thyratrons made by Hygrade Sylvania Corporation under our direction.

The NCR type tube has approximately the following characteristics:

  • Heater – 3.2 volts AC
  •           .6 amperes
  •          1.9 watts
  • Plate votage = +125 volts
  • Grid ignition mº = -12.5 volts
  • Grid current (tube conducting) = 150 µ amp
  •           (with -100 volts applied through 1/2 meg resistor)
  • Maximum anode current = 25 ma
  • Anode-cathode drop = 16 volts
  • Grid-anode test breakdown voltage = 400 volts
  •           Cgp = 1.3 µµfd
  •           Cgk = 3.5 µµfd
  •           Cpk = 1.6 µµfd
  •           Base = bakelite, plugs into amphenol tpe 848
  • Envelope = glass, 2-7/32 long by 25/32″ diameter

The Sylvania tube has approximately the following characteristics:

  • Heater – 2.5 volts AC
  •           .615 amperes
  •          1.53 watts


  • Plate voltage = +125 volts
  • Grid ignition voltage = 12.5 volts
  • Grid current = 160 µ amps (with -100 volts applied through 1/2 meg. resistor)
  • (tube conducting)
  • Maximuym anode current – 25 ma.
  • Anode-cathode drop = 15 volts
  • Grid-anode test breakdown voltage = 400 volts
  •       Cgp – 2.5 µµfd
  •       Cgk – 1.5 µµfd
  •       Cpk 1 µµfd
  • Base -button type 7 pin
  • Envelope – glass, 1-3/4″ long by 11/16: diameter

A curve showing grid ignition potentials for various anode potentials is included herewith. The Hygrade tube, designed to replace our laboratory produced miniature tube has not been released as yet and is still in the experimental stage. We are working with the in an effort to remove a few more objectionable features. Within 60 days the Hygrade tube should be satisfactory for production. You will probably find the four Hygrade tubes we are shipping to be perfectly satisfactory. If not, raise the heater potential to 2.75 volts so as to increase the emission slightly. Do not exceedthis value however. Later designs will have some safety feature in the tube construction contributing to longer useful life.

We will be glad to receive your report as to the behavior of these tubes in your circuits. Should you need it, we will furnish you any further information that may become available. We might refer you to Mr. John Coleman of Section D3, Instruments, MIT Office of NDRC at the Massachusetts Institute of Technology, Cambridge, Massachusetts for information as to the actual use of these tubes in experimental devices.

Sincerely yours

Joseph R. Desch, Mgr. Electrical Research Laboratory

Carbon copies to – John S. Coleman, Harry M. Williams, Carl Beust