2A3 SE Amp

[widowmaker]

Approx. 30W anode dissipation for 2A3, 6 months, no problems!
Plasma tube is originally developed by Asparuh Jeliazkov, constructor of BG Full Range driver named "Ether".
It is quite different from classic VR tubes.
For non plasma tube applications :
Simply change two 5k1 resistors with others, with value 68k/1W.
Caps are 3TO-1 or K52-2, AgTa, russian military made.
I tried with many brands - Paper in oil (really greasy sound, wich masking faults of amp and source and we think that sound is OK), BG (slower than K52-2 with "anaemic" sound )...

Schematic:

[Zoran]

Nice design,..
What about sound

[Alastair E]

Just curious.....

Why have you used a string of electrolytics for coupling the grid of the 2A3 from the driver and from the gain stage to driver....?

Personally, I wouldnt trust an electrolytic here as they as just so leaky and could cause bias drift, Maybe I'm wrong though....

I like good old fashioned Polyprop caps for that job, and you only need the one....

Something you may have overlooked....

Your 6.3V supply for your Driver/pre And the rectifier (The Cathode of which is at 350 odd Volts),--Also supplies the driver/pre tubes whose Cathodes are near earth/deck potential......

You Could be exceeding the Heater/Cathode potential of both the rectifier and the pre/driver tubes....Worth checking--I'm not familiar with that rectifier tube....

[widowmaker]

6ã4ð-å÷ has max. +100/-400V between heater and cathode
It's really great rectifier tube

[Gordy]

Your designs are always interesting, so I shall keep an eye on this project. Good luck with it.

[widowmaker]

Originally posted by Alastair E Just curious.....

Why have you used a string of electrolytics for coupling the grid of the 2A3 from the driver and from the gain stage to driver....?

Personally, I wouldnt trust an electrolytic here as they as just so leaky and could cause bias drift, Maybe I'm wrong though....

I like good old fashioned Polyprop caps for that job, and you only need the one....

Russian military AgTa cap has quite different construction (without plates) than other ordinary caps - (your favorite) polyprops, electrolytics, etc.

[widowmaker]

construction of AgTa caps, K52; 53; 3TO, etc. :
see image
peculiarity of construction explains why these caps are too fast and linear...
where to buy?:
click (russian)
Caps 3TO-1;2 are old production of K52-2 type and has different (a little bit bigger than K52-2) geometric dimensions.

[Zoran]

I have excellent experience with russian military PIO caps (brown col. like cigaret pack, metal box...) Even open one to take a look what is inside... And there was I think silver foil paper insulation in gel...
Sound was superior to against poly teflon and other caps...

[widowmaker]

Russian military silver-mica caps also sounds good.
I have few scores (taken from old wasted russian missles) and I use them for RIAA correctors...

[widowmaker]