I am trying to build a tube amp without using any semiconductors (just for the fun of it, trying to make it using the technology that was available when tube amps were mainstream). I may need to control some relays in it, however, I cannot figure out how, or rather, how to do it properly.

I have some thyratrons (both hot and cold cathode) and obviously some vacuum tubes. I may have to:

  1. turn a relay on or off with a pulse (like a push button)
  2. Switch between two relays (one off one on)
  3. have a relay turn on for some time then turn off (shorting the output of the amp for a few seonds to avoid a pop when switching inputs etc).

How do I do it without semiconductors? I currently do not have a specific application in mind, just looking to learn more.


1 Answer 1


To 1st and 2nd problem you need a simple flip-flop. You can make it from two triodes or one dual triode. Look at this schematic from DRTE Computer site:

enter image description here

Outputs are on anodes of tubes. One output have high level and other have a low level, trigger pulse swap levels of outputs. There are many vacuum-tube flip-flops like this one, similar in construction, and all of them have its origin in first ever know digital circuit: Eccles-Jordan flip-flop.

Solution to the 3rd problem is single-shot multivibrator:

enter image description here

Output is on the A2 anode. Values of R and C connected to A1 anode gives You a time of output pulse duration. This circuit comes from P.Neeteson book "Vacuum valves in pulse technique", page 117. Another circuit You may found here: http://mysite.du.edu/~etuttle/electron/elect36.htm

There are also other solution to control relays without transistors and also without tubes - You may use only relays. But I suppose that it will be hard to find old "non-electronic" (fully electro-mechanical) pulse-trigerred and time delay relays - eBay and flea-markets should be Your friends.

  • \$\begingroup\$ Completely forgot about flip-flops. I guess when I am thinking about tubes I am not thinking about digital circuits. \$\endgroup\$
    – Pentium100
    May 25, 2015 at 11:57

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