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 see some similarities which I appreciate. Intriguing work gentlemen.

@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

 

[Doug De Young]

Measurements finished up.

 

[Doug De Young]

Also some nice photos of the finished build

 

[Drewaudio]

That looks amazing! Nice work

 

[potepuh]

can you share the gerbers?

 

[Sorento]

All tube version of se cascode output from the "goldmine" thread on this forum:
https://www.diyaudio.com/community/attachments/ta300b-png.783034/

 

[Doug De Young]

can you share the gerbers?

Still deciding what to do about offering up the PCBs and such. You’re of course welcome to use the circuit to develop your own PCBs in the meantime if you want.

 

[Doug De Young]

All tube version of se cascode output from the "goldmine" thread on this forum:
https://www.diyaudio.com/community/attachments/ta300b-png.783034/

Very cool!

 

[astouffer]

Isn’t the 50CA10 pretty rare these days?

 

[Doug De Young]

I’d probably go with a pentode on the bottom if I was designing. But don’t have a ton of experience with cascode output stages. I’ve only designed one! 😂

 

[dubadub]

Congrats. Have you considered using this drive circuit with a GU-50 in SE?

 

[Doug De Young]

I really should. I have so many GU50. Love that tube.

 

[Drewaudio]

Out of interest, what is you cnc machine??

thanks Andrew