Moscow resident Dmitri Gubchenko made the Demograf.
https://www.head-fi.org/threads/the-stax-thread-iii.677809/page-197#post-10809881
https://www.head-fi.org/threads/the-stax-thread-iii.677809/page-197#post-10809881
I'm pissed you found this at an auction ! 😳
One of the best headphone amp in the world...
normally you should find it inside.
One of the best headphone amp in the world...
normally you should find it inside.
El156s won't fit, as there are two O/B5, V, and G8A sockets each. EL156's require G10A sockets.
Best regards!
Best regards!
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A little more information
https://hifiphilosophy.com/demograf-najlepszy-wzmacniacz-elektostatyczny-na-swiecie/
https://hifiphilosophy.com/demograf-najlepszy-wzmacniacz-elektostatyczny-na-swiecie/
Input valves are B5 or even B4, could be REN904 types - really good triode, mu of around 30. I've used that myself and its equivalents.
Output valves are side contact by the look of it. Not so sure there. Check the filament voltages for these old 1930s valves - likely to be 4V.
For low power there's the side contact EL3n, which is very good. I've used its successor the EL33 in triode.
I can't quite see the other 2 sockets, look like miniature side contact. Never seen any of those.
The amp is clearly a homage to radio/broadcast amps of the 1930s.
Output valves are side contact by the look of it. Not so sure there. Check the filament voltages for these old 1930s valves - likely to be 4V.
For low power there's the side contact EL3n, which is very good. I've used its successor the EL33 in triode.
I can't quite see the other 2 sockets, look like miniature side contact. Never seen any of those.
The amp is clearly a homage to radio/broadcast amps of the 1930s.
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Just had a look in the guts - this thing defies all logic. Output terminals worthy of an arc welder. A headphone amp I can just only lift (and it obviously needs an external PSU). Cannot figure out the tube types (and I've been around tubes a loooong time). Still, if I ever need a mooring for a boat, I could do worse for $90....
Attachments
You have possibly one early version (unique) of an electrostatic headphone amplifier from Dmitry Gubchenko or a clone.
The tubes in front are EL8?
More info here:
https://www.head-fi.org/threads/the-stax-thread-iii.677809/page-5#post-9737391
The tubes in front are EL8?
More info here:
https://www.head-fi.org/threads/the-stax-thread-iii.677809/page-5#post-9737391
There is no published schematic for it. Need to reverse-engineer it. Post #3 shows the power supply.
Supposedly based on the Western Electric 7A amplifier. Front 4 xEL8, back 6SN7
Supposedly based on the Western Electric 7A amplifier. Front 4 xEL8, back 6SN7
By looking at the related pic in #1 I was quite sure that the side pin sockets were 5-pin. But due to your latest pics from the innards I'm not that sure anymore. Would you please count?
Best regards!
Best regards!
It will work with a REN904 type in the input driving the side contact outputs directly. Or equivalents AG495, E428, A4110, K1694. All 4V. I have quite a few of these types - mu 30 and good sound. Ri is around 12K, though.
For side contact, like I said, EL3n (4V) is an affordable output. Higher prices for EL50, 4654, 4699 (6.3V) though they have more power.
For side contact, like I said, EL3n (4V) is an affordable output. Higher prices for EL50, 4654, 4699 (6.3V) though they have more power.
So it is 8 pin side contact?
Btw, EL3N is 6.3 V. The same tube with 4 V heater is AL4.
Best regards!
Btw, EL3N is 6.3 V. The same tube with 4 V heater is AL4.
Best regards!
Quite another idea: There's at least one more variant of the AL4/EL3N family: EL11 is an EL3N with that 8 pin German Telefunken 'Stahlroehren' octal base. As there's a pair of exactly these sockets, EL11 might be the output tubes as well.
Best regards!
Best regards!
No - the Y8A socket for the EL11 is the same size as the side contact one - it isn't the "mystery" small side contact socket on each side. The EL11 is an excellent valve - I've used that and it's maybe a smidge better than the EL33 (successor to AL4) in triode. The Y8A socket also takes the EL12, which is excellent, and usefully the much cheaper EL12n which is an E.German later version and available new from German dealers. I've used all these myself in triode and the EL12n is probably the one I'd go for for 18W dissipation. But I can't see a Y8A socket here. Could be swapped with the side contact one. Or fit a big ceramic octal socket instead and get lots of choice.
As AL4, EL3N, EL11 and EL33 all have the same innards, I have to ask what's the reasoning behind this claim?
Best regards!