[HOW] to clean FET-Octave-UP 45 years ago...

[puretube]

i.e.: 7 years before AN-32... :

page2 fig. 6 & 7...

Why?

...coz they didn`t make FETs like they used to 50 years ago anymore...




hey, won`t you tell me, where have all the dual-gates gone   

[JDoyle]

hey, won`t you tell me, where have all the dual-gates gone   

They all evolved, or rather were killed off, like their single gate brethren, into dual gate MOSFETs.

America only every made two that I know of, the 3N96 and 3N97. I couldn't find them, good luck if you try.

The Japanese made a few too: 3SK22, 3SK23, 3SK28, 3sk30/A (no p-ch/2SJ types that I know of other than the 3SJ11/A but thats MOS).

All that said, if you can find an old JFET in a TO72 case (four pins) and the fourth pin is specifically noted to be connected to the substrate, that can be used as a second gate. It is the same thing, it just won't have been specifically designed to be used as such, and therefore will have a higher parasitic capacitance, making it useless for what the dual gate FET is designed for - high frequencies. That doesn't mean that it won't work for audio.

If the fourth pin is the case, it's a crapshoot, the case might be attached to the substrate. It might not. It might be attached to ONLY the case or it might be attached to the 'real' gate - which is often the situation with metal can JFETs without a fourth pin, and that can be a HUGE pain in the ass if it ends up touching something inside the box after it is all closed up.

Trust me on that, I've got experience.

For what it's worth,

Jay Doyle

[puretube]

Jay, after seeing your name in the "users online"-list right after having submitted the post ,
I just new you were going to write the first reply 

actually, I`m not whining after the dual-gate mosfets they made for RF-purposes,
but just had that old Kinks hit in my ear while typing that last line...

fig.7 is just an example of: it`s been out there even before some kids who think to have freed the stompboxworld with their de-gooping skills,
were even born...

[frank_p]

Jay, after seeing your name in the "users online"-list right after having submitted the post ,
I just new you were going to write the first reply 

I had this idea too...  But don't know exactly why  .
Great read, thanks PT.

[Ice-9]

i.e.: 7 years before AN-32... :

page2 fig. 6 & 7...

hey, won`t you tell me, where have all the dual-gates gone   

Yeah i instantly thought of van halen "where have all the good times gone" which is obviously a cover of the Kinks

[puretube]

Bowie`d ? 

(though i seem to hear some Roxy in that one...)

[R.G.]

Pretty cool. He invented the JFET doubler independently. But twenty years earlier! 

As a single silicon device, no less. He even describes it correctly. But there's obviously an advantage with being able to cook your own dual-gate devices instead of matching discretes.

I bow in his honor.

[gez]

Briefly clicked on the links last night and didn't really take it in.  As I awoke this morning, my first thought was, "Oh, yeah, I see now".  Funny how the mind works.  Cool idea.

I suppose breakthroughs are happening all the time these days, but it's all in the digital domain so I never realise.

PS  I enjoyed 'singing' (you should hear my voice!) along to the Kinks.