Saturday, February 10, 2018

The Super Regen with a Mosfet?

A TRB member was looking at a vacuum tube Super Regen and asked can it be done with a FET? This is the circuit in question.

He offered this as an option.

The first step should be to look at how a Super Regen works.

The Regen is turned into a Super Regen by adding a switching circuit in the grid. So what does that do for us?
Ok the regen is oscillating and the quench breaks those oscillation up. The high frequency spurts are above our hearing range.
Input a modulated signal and the spurts are modulated at and audio rate. (follows the envelope.)

Now the original question. Can it be done with a FET?
I'm using a 2SK669 MOSFET. I bought a reel at 2 cents each so this is my go to MOSFET. I think a 2N7002 would be a close match. Anyway as you can see I used a transformer with three windings.
I adjusted the coils a little to see how it effected the circuit.
I think a pot across the feed back coil would be a good option.
You can see the coil on the gate is 1 millihenry. I wound a piece of wire about 24" long on a core (blue) and it was 1.8 millihenry. Putting a pot across the feedback coil would allow adjusting the circuit with a toroid core coil. So the original question, is it doable? The answer would be found by trying it.
This circuit would only require the input tank to be adjustable. The quench circuit could be fix tuned and the feedback could be adjusted with a pot.
The blue coil frequency response is up to 1Mhz.

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