I am working on making a flyback driver with a 555 timer. The only part I need is a MOSFET power transistor. I am wondering is it possible to substitute a triode vaccum tube (14GT8) for the MOSFET?

  • 4
    \$\begingroup\$ The humor of driving a vacuum tube with a 555 has not been lost on me. \$\endgroup\$
    – user3624
    Commented Sep 20, 2012 at 2:59
  • 1
    \$\begingroup\$ It is interesting that so far you have not accepted a single answer. Do none of the answers to your questions you received so far solve your problems? \$\endgroup\$
    – AndrejaKo
    Commented Sep 20, 2012 at 13:17

1 Answer 1


Please clarify whether you wish to use a MOSFET or a vacuum tube in the final design.

If you are looking at an older tube or an old circuit then the abbreviation 14GTB may have been used for a range of vacuum tubes.
G T B = Glass, tubular, version B (as opposed to GTA = version A)
so GTB on the end does not tell you a lot about the tube's functionality.

Do you have a circuit diagram?
Please provide more details.

MOSFET in place of a vacuum tube:

BUT, yes, if you want to use a MOSFET in place of a vacuum tube (in old equipment or using a very old circuit) and you want to drive it with a 555 to make a flyback driver you can do so, subject to getting a MOSFET that meets the circuit needs. The MOSFET would need a high enough voltage rating to survive the inductive peak on its drain during flyback, and it needs a high enough current rating to meet the circuit's design. You will need to use an N Channel MOSFET to get the polarity correct.

Vacuum tube in place of a MOSFET:

If you want to use a vacuum tube in place of a MOSFET it MAY be possible but will need good design knowledge as VT's are somewhat harder devices to drive. (Correct grid biases, limited current, higher voltages, heaters, ...).


Many vacuum tubes for sale here

Some GTB suffix tubes


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