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-   -   O.H. Schade(1938) meets MOSFET (http://www.diyaudio.com/forums/pass-labs/144105-o-h-schade-1938-meets-mosfet.html)

revintage 14th May 2009 08:37 AM

O.H. Schade(1938) meets MOSFET
 
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Lately there has been quite a few threads covering the work of OH Schade 1938, http://www.clarisonus.com/Archives/T...er%20Tubes.pdf . He showed how a tetrode could get triode characteristics with the help of what he called "inverse-voltage feedback". While working as a triode the efficiency of the tetrode was still kept.

On the left is a tube SE in accordance to his suggestion. It has the same output impedance and distortion characteristics as if it had been triode-strapped but twice the output power! On the right the output device is substituted by a common MOSFET that according to Schades suggestion is feedbacked ca 20dB.

Seeing any similarity with a Zen:cool:?

By the use of an IT there is a better chance of getting much better HF-bandwith. The example sims with a -3dB point in the region of 100kHz.

revintage 14th May 2009 08:41 AM

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A MOSFET has pentode-like characteristics.

With shunt-feedback(inverse-voltage feedback) applied they change to triode-like.

But this old news for the most of you;) !

Nelson Pass 14th May 2009 03:19 PM

Very Excellent.

:cool:

revintage 15th May 2009 10:51 AM

Letīs Schade the 2SK170
 
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So what happens if we adapt what Schade taught us to a JFET as buffer?

Works like wonders:D !

Zout below 200ohms, together with low THD and acceptable bandwith (-3dB at well over 200kHz). Zin chosen to 10kohm. With 22kohm/91k bandwith is 100kHz.

But donīt try to a volume-pot at the input! Must be fed from a lowZ source.


MRupp 15th May 2009 11:06 AM

Very interesting buffer concept, but off course it inverts phase, so where you need this ... and it also looks pretty similar to the buffer in the alephono MC stage ;)

revintage 15th May 2009 11:18 AM

Quote:

but off course it inverts phase
Is this a problem? If so, just shift plus and minus on your speaker terminals;) .

MRupp 15th May 2009 12:21 PM

Not a problem at all (as long as you keep track of the number of times you change phase in your system and do not switch to and fro inverting / non-inverting stages), and it should be useful where you have a requirement to revert phase ....

Nelson Pass 15th May 2009 06:49 PM

Re: Letīs Schade the 2SK170
 
Quote:

Originally posted by revintage
Zout below 200ohms, together with low THD and acceptable bandwith (-3dB at well over 200kHz). Zin chosen to 10kohm. With 22kohm/91k bandwith is 100kHz.

But donīt try to a volume-pot at the input! Must be fed from a lowZ source.

You don't need R10. This circuit works to provide a virtual ground at the
Gate of the JFET, so the input Z is 10 Kohm as shown. Actually you can drive
it with a range of source impedances, and adding a pot as high as 25K should
work fine.

:cool:

kenpeter 16th May 2009 12:02 AM

HighZ lowZ, don't matter. As long as its stable with frequency.
It just becomes part of the feedback divider...

There's a nice photo of a curve trace for a similar circuit:
http://www.radiomuseum.org/forum/the...ate_triode.htm

The only difference, Trioderizer gate is battery biased.
A battery could last a long time, if its only biasing gate...
I imagine you would want to bypass with a good cap???

something weird with that link. You have to find it the hard way...

Forum ŧ
Technique, Repair, Restaurtion, Home construction ** ŧ
Home construction and general radio technique ŧ
The Trioderizer - a solid state triode

chinsettawong 16th May 2009 03:40 AM

Very interesting! :)

Wachara C.


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