Electronic – Are vacuums tubes suitable for switching high current (~30amps) at high frequencies (~K-Mhz)

high frequencyhigh-currentswitches

I was looking to build a system for high currents (say ~30 amps) and a friend suggested vacuum tubes. In theory, vacuum tubes seemed more robust for high current applications, but after looking around, and I found a bunch with relatively low current ratings (~10mA.)

I wanted to avoid mechanical relays if possible because they seemed a poor design for high speeds. I also preferred to use a CMOS type design–my setup is symmetric with respect to p-channel and n-channel MOSFETs (at least in my circuit simulator.) I noticed some vacuum tubes have a dual gate–which fits perfectly into my design. The question is whether they can handle these currents at high speeds.

My voltage should be quite low ~50V.

I am designing an induction heater, but I am trying a different approach in which I treat the heating element and the object to be heated as a black box, and use the proper switching elements to counter whatever voltage the black box produces. That is the basic idea. There is obviously more to it (e.g. have the switch on only after a threshold voltage, and off beyond another threshold voltage that would damage the circuit.)
Anyway, it was just something I wanted to try, and thus far, it seems like a relatively cheap project considering I can get a lot of parts from old stuff at yard sales, ebay, etc.

Best Answer

A very short answer with not too much detail goes like this:

  • Tubes are good at medium to high voltage and low current.

  • Transistors (especially MOSFETs) are good at low to medium voltage and high current.

Exceptions exist, but for the common and most used examples of said parts, the above... ahem... selection guide is a start.

For fast (> 10 kHz) switching applications based on tubes, you may want to look into (literature for) horizontal deflection circuits in old (pre-1970) TV sets.