What is from your view the main disadvantage by circuit from post #18 in opposite to that one from post #17 ?
The input cascode (at first look a differential amp) from post #17 provides rather an advantage compare with a normal one-stage input section from post #18.
OTOH - crucial should be the audible differences between both solutions.
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I am selling this book
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In the Frank Blöhbaum article it described only a useless configuration called "best pentode"
Here two other circlotron topologies:
http://www.diyaudio.com/forums/pass-labs/75644-my-jfet-project.html
http://www.diyaudio.com/forums/pass-labs/130810-amazing-fet-circlotron-mike-rothacher.html
I would try to replace the tube with a VAS stage like this (introduced magic resistor and cascoded cascode):
http://peufeu.free.fr/audio/memory/memory-5-vas.html
This topology must actually clearly beat all exist small signal tubes in all respects, as long as high supply voltage is still present.
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Andrea,
one little reminder: could you please anwser my question #30?
I monitor your circuit adventures. I wonder that your proof of concept didn`t blow up the main fuse. A little shift of tube anode current will cause a huge change of Mosfet drain current. I guess you have made some of these experiences. Your last circuit is a step in the right direction. But it violates Franks patent. Private use will be no problem but be careful with commercializing.
one little reminder: could you please anwser my question #30?
I monitor your circuit adventures. I wonder that your proof of concept didn`t blow up the main fuse. A little shift of tube anode current will cause a huge change of Mosfet drain current. I guess you have made some of these experiences. Your last circuit is a step in the right direction. But it violates Franks patent. Private use will be no problem but be careful with commercializing.
about question #30:
The main advantage of the configuration called "best pentode" is the very high voltage gain, but where can be necessary where this ? probably with a cascode you can create the same result.
I have buy this book to serach something about the second stage of teh Thorens.
Do you think there is a Franks patent violation on the new circuit using a current generator on driver stage ? The patent shoud be about the strange feedback create with difference and sum using opamp
The main advantage of the configuration called "best pentode" is the very high voltage gain, but where can be necessary where this ? probably with a cascode you can create the same result.
I have buy this book to serach something about the second stage of teh Thorens.
Do you think there is a Franks patent violation on the new circuit using a current generator on driver stage ? The patent shoud be about the strange feedback create with difference and sum using opamp
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