It's not often you see these in modern gear.

https://en.wikipedia.org/wiki/Static_induction_transistor







Highly unobtainium today but I have a few 'donor' machines to replace the shorted devices.

 

I do recall that VFETs were all the rage in hifi equipment. Late 70s, early 80s. Several japanese manufacturers adapted it, but for some reason never became a mainstream component.
The devices were quietly discontinued, and nowadays any functional device has its weight worth in gold.

 

They have very tube like trace curves so you could get the tube sound harmonics that some seem to love.


I've Frankenstein'd (no schematics) two broken devices to get one that at least has transducer output power to a dummy load.
The ultrasonic output circuit is similar to the application circuit.

 

Is it operating in class B?

 

Is it operating in class B?

Likely running class C (guess from the bias and device drive voltages) as it's just a carrier power generator to a transducer plate that's part of a nano level particle removal process.

https://pctsystems.com/megasonic-cleaning-technology/

Example systems.

 

I checked Ebay listings. Boy, are these transistors expensive!!
A pair of 2SK180 for $240US

 

I checked Ebay listings. Boy, are these transistors expensive!!
A pair of 2SK180 for $240US

Cheap, if it will fix the problem.
https://www.ebay.com/itm/395434351368

 

I totally get the $4200 asking price, but the $700 for shipping?!?
Do they ship it in an armored vehicle?

 

I totally get the $4200 asking price, but the $700 for shipping?!?
Do they ship it in an armored vehicle?

It's the normal shipping scam to have lower prices during searches.