EL34 A2 Cascode SE triode

[Doug De Young]

It’s a pair. The shipping can be quite high though. Still it’s pretty good value.

 

[Francois G]

Also following this design with interest. The Mosfet in the schematic 10N60C seems to be obsolete. Will this one work in its place?

https://www.mouser.com/ProductDetail/STMicroelectronics/STP10N60M2?qs=DqCdCwOw4/5AmMf4xasHww==

Is this based on the Tubelab UNSET, or am I confused?

 

[Doug De Young]

That MOSFET isn’t rated for DC in the SOA so I’d look for one that can handle DC. 600v is unnecessary and RDS ON is not important in this application. 400v is more than sufficient. The 10N60 is still available.

I was unaware of TubeLab’s UNSET when I designed this and any similarities are coincidental.

 

[Doug De Young]

Preliminary test results. Here is calibrated voltage noise into 8R. The amp input is shorted. All hum components below 100uV. Pretty good for SE cascode with AC heaters. PSRR is very poor.

 

[Doug De Young]

Preliminary 1w FFT. I may roll tubes to see if I can lower this. Still .17% mostly second is not bad.

 

[Drewaudio]

Nice!

 

[jcalvarez]

Is this based on the Tubelab UNSET, or am I confused?

There are similar bits, like the operation of the output tube in common g1, but apart from that is pretty different. There is no direct feedback (both DC and AC) from plate to g1, feels like a Schade-style feedback from plate to plate. Then the driving mosfet is not a follower, it is an amplifying stage. Then it has feedback from the output windings to the driving mosfet.

 

[Francois G]

Thanks for pointing out the differences @jcalvarez. I still see a lot of similarities. Intriguing work gentlemen, and thank you for sharing.

@Doug De Young, if you have not looked at it yet you might find the Tubelab UNSET development interesting. See here: https://www.diyaudio.com/community/threads/unset-beta-board-build.376124/page-29#post-7645393