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?
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, ...).