Beauty in a Vacuum: Tube pics and close-ups

paulbottlehead

Active Member
Hi Paulbottlehead,
Nice looking amp. Can you share a schematic or describe its circuit in little more details? Thanks.
David
The 810 is run at about 650V and 180mA. The driver is an EF86 run as a pentode feeding a pair of 12GN7 triode wired pentodes acting as cathode followers, and they are directly coupled to the 810's grid. There is a -100V rail and a solid state constant current source under the cathodes of the 12GN7 tubes to provide them adequate operating current when the 810 grid isn't. I added a couple of VR-105 voltage regulator tubes between B+ and the driver supply to knock the 650V down to more reasonable levels. The 810 tube is DC heated with a choke input filter fed by a bridge of very beefy Schottky diodes tabbed down to the chassis. I managed to get 50WPC @ 10% THD and a damping factor of 5 with only local feedback, though I have enough gain leftover that I could switch in 6dB of feedback around the OT to get more damping if required. Each amp weighs 64 lbs, and the customer is now finally convinced that a stereo amp wasn't the right choice!

I'm not planning to post a schematic, but work on this project has lead me to consider doing a lighter 30W design that will work with tubes like the 805, 838, 203A, etc. that would be a far more reasonable DIY project to publish.
 

mhardy6647

Señor Member
yeppers.
I would say so called meshplate -- more like perforated plate.

Kinda garish lookin' tubes, but pretty in the dark* and pretty good sounding, too.

meshplate2A3 by Mark Hardy, on Flickr

EDIT: oh, that's a very nice photo of one that you posted earlier, @Redboy!
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* I'd add some sort of insensitve, tactless, sexist comment here -- but of course I am above such antics 🧐
 
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