[Sodacose]

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The Starving Student was the first tube amp I ever wired point to point. Unfortunately those 19J6s are getting hard to find. Here's another spin on the same 48V tube+MOSFET buffer theme using a 7370 tube (5687 with 40V heaters). As tribute to Pete Millett, I'm calling it El Estudiante.
 
You can read more about the design, etc, on my project website here: https://wtfamps.wordpress.com/el-estudiante-headphone-amp/
 
No commercial interest.  Just giving back to the community that first convinced me to jump into the tube audio pool and learn to swim.
 
Now quick jump on eBay and grab some 7370s while they're still $5 a piece!

 

[100VoltTube]

Those tubes don't look too linear with such a low B+. I think it would be cool to try a 6BF7 (datasheet) But if it sounds good, then there's no real problem.
 
BTW I love your website! It is the best place on the web for learning the basics of tube audio amp design IMO. I am one person who you demystified tube amps for. Keep up the good work!

 

[Sodacose]

Thanks for your kind words, 100volttube.

Truth is there's very little short of space charge tubes that is going to be linear at 48v B+. From just looking at plate curves though, the 5687 does much better than most.

Well enough that a 3x Rp load will let the grid bias negative with a couple ma current through it. A lot of other tubes need extremely large loads and miniscule current to pull it off.

I'd be very interested to try the same amp with a choke load like the Hammond 156C, but that about doubles the cost and makes it a conceptually more advanced amplifier.

edit to show actual bias point:

 

[LennySmelcer]

Hello
You are a good and smart guy because you are participating in such projects for students. I want to participate in such projects, for which students develop devices - it is interesting for me. But I have one problem that the site, about which you can read more decides, it will write for me a proposal for research which I can submit for consideration to participate in such a project. I'm a true mechanic and I'm not a creative person, therefore I cannot write a proposal for research on my own. It is good that such companies exist.

 

[DutchGFX]

Interesting take. I've never actually built a SS, but I might add some CCS and a boosted follower and build one...

If we are going to suggest tubes, I'll toss in the 12AE6. It's designed for around 40V on the plate, and draws barely any current. The only issue is the heater is 12.6V at 1.5A, but since you need 2 tubes, you could get 24V which would limit the power dissipated by a dropping resistor to 3.6W, which isn't so bad.