HV cascode FET Booster

Hi guys,

i´m trying to design a small Booster to switch in front of the famous tube DI that´s around here. The supply voltage is about 180V. There´s a 33V Zener diode on the gate of the MOSFET to keep the JFET in a safe operating range. It´s an experiment and i´m not shure how it will behave in reality. So before i fry something could anyone with more experience than me take a look at the schematic.

I only want a fixed Boost with 20dB that´s why the load resistor is so small. I don´t care that much about THD but i would like to keep it low noise. Maybe there are even better options out there i couldn´t think of so far.

Thanks.

I thinl  R26 may be too high at 1Meg. You normally aim for 1mA at least through the zener. You are dropping about 150V so 150K m8ight be a better value.

Cheers

Ian

Thanks Ian!

It was just an experiment. I should have noticed that.

At the end of the day a normal booster pedal can do the job.

Sometimes it takes time to get to the obvious solution

> the load resistor is so small.

It does not make much engineering sense to start with 180V, drop it in 100K, then load with 5K. Sorta making a toothpick out of a tree.

Use the 5K as the DC feed. Right away you may only need 5/100 of the supply voltage. At that point you are well within ratings of 2SK170, and can lose the MOSFET. At this low gain the cascode gets you no benefit, only more parts.

> a normal booster pedal can do the job.

Or that, yes.

Thanks PRR!

The 180V came from the Tube Supply.
I thought it would be cool to have it in one Box without the need of an another power supply. But the circuit you show here seems much more appropriate.

Why not use a subminiature  or a seven pin tube? This would be a perfect match for you existing PSU.

MRecords said:

Thanks PRR!

The 180V came from the Tube Supply.
I thought it would be cool to have it in one Box without the need of an another power supply. But the circuit you show here seems much more appropriate.

Click to expand...

Stepping down 180V to 18V is trivial.