Exotic component from 70´s

[Nasse]

Sorry for low quality pic, my kids took the digital camera.

Remebered I have this pic in old 70´s magazine, when Mark Hammer discussed ROG amp simulators at higher supply voltages.  A "fetron" is a component that was used in 70´s and you can plug it straight in a tube circuit, Google knew that some Mesa Boogie MkII´s had a fetron in its preamp

Don´t worry if you don´t see any component values at the pic, they are just theoretical symbols like RL or Rg etc.

What I understand FETRON is for preamp stuff only, input and output impedance is even higher than real tubes. But I wonder if you could construct your own "fetron" just by connecting two jfets like inside the circle in the pic. I believe they used some kind of high voltage jfets in fetrons.

[puretube]

Good morning to Suomi !
thanx for that info!

I thought the Boogies just had constant current sources in them
(like a FET with G/S resistor - 2 pole devices) ??

[Nasse]

I thought the Boogies just had constant current sources in them
(like a FET with G/S resistor - 2 pole devices) ??

The component used in Boogie may be different than what in my picture. I found the component type number used in Boogie easily with google, but could not find datasheet. Just found the whole old magazine in my cupboard, and there is another pic and some more info on the first page, and it says in some pic text something like: "Most Fetrons are constructed of two jfets in bootstrap (constant current) or cascode circuit. Miller capacitance phenomenon is minimised by using small capacitance high gain device as input fet, connected to high voltage output fet". I think that is enough info for some experimenting. The other pic has better markings where to connect S, D and G´s, and the example fetron uses 2N3823 as input device and 2N4882 as output device. I´ll try to post that other pic later today.

Quess nothing new to except distortion wise, jfets and minibooster applications are tried and tested methods already. Fetrons seem to be very clean and clip not so softly as tubes, and don´t know the drawbacks.

[Paul Perry (Frostwave)]

Plenty abt them via google, apparently used in guitar amps to avoid microphonics. Major commercial use in telephone carrier distribution boosters. A metal unit half the height of a 12AX7 with same pins, but maybe not as high a max voltage.

[cd]

Not to mention they sounded horrible.  Well, in Boogies at least.

[Nasse]

Not to mention they sounded horrible. Well, in Boogies at least.

That´s what I was afraid. Could be the reason why I have not heard about them lately.

Cheers

[Nasse]

Took few pics more, before dumping the subject in a deep hole, need to practice that camera. Cheapo digital cameras seem to be tricky...

There is a lousy picture of physical look of a Fetron, and an example cascode circuit.

http://img.photobucket.com/albums/v411/Nasse/ftronix1.jpg
http://img.photobucket.com/albums/v411/Nasse/ftron2.jpg

This is just low-forehead fake-yourself a mad scientist experimenting with dangerous high voltages propellerhead stuff

oops I removed the pic from first message, I´ll fix that later with a better (?) quality pic