6L6 Ultralinear cathode Follower

[revintage]

And probably was unenforcable anyway as Broskie mentions prior art and plain obviousness from UL.

This is somewhat above my English. But Broskie didn´t publish his "innovation" until 2000. I have though seen something in this direction in a very old German paper from the 50´s that I unfortunately can not find.

But what should the advantage be to use it as driver?

In our amps we call it TULP(Triode-UL-Pentode) as it is continously variable.

[Merlinb]

Originally Posted by revintage

This is somewhat above my English. But Broskie didn´t publish his "innovation" until 2000. I have though seen something in this direction in a very old German paper from the 50´s that I unfortunately can not find.

The patent is indeed obvious, and overruled by prior art. The topology is mentioned (and dismissed) in:

Butler, F. Transistor Wide-band Cascade Amplifiers. Wireless World, March 1965. p125.

"Fig. 4 is another circuit which at first sight looks promising but which, on closer investigation, turns out to be rather disappointing... Moreover the reduced output impedance is achieved at the expense of disproportionate reduction of gain."

[cbdb]

Myself I like the Hightened detail and crisp high end of the cathode connection.

Shouldn't that read: Myself I like the EXTRA DISTORTION of the cathode connection.

[ppl]

Originally Posted by cbdb

Shouldn't that read: Myself I like the EXTRA DISTORTION of the cathode connection.

No because the Measured THD at the Headphone output is less with the return to the cathode this is most apparent above 10KHz.

[ppl]

Originally Posted by smoking-amp

How about taking the cascode grid's feedback off a tap from the final follower output?

That is a great sugestion and indeed it dose work great (I tried it at your suggestion) however that Topology may Be covered by U.S. patent number 4,647,872 ? Granted the patent is intended for Bipolar transistors. thanks for that Idea.

[smoking-amp]

"however that Topology may Be covered by U.S. patent number 4,647,872 ?"

1987 patent, 20 years coverage till 2007, so expired anyway.

[DF96]

Originally Posted by ppl

No because the Measured THD at the Headphone output is less with the return to the cathode this is most apparent above 10KHz.

You may be getting some cancellation. A little degeneration can cancel third-order for an exponential device, such as BJT or remote cutoff valve. A little positive feedback might cancel third-order for a conventional valve (which curves the other way).

[ppl]

It looks like that the Tube Cad Tetra Sans also uses some positive cathode feedback.