Received some of those German "postroehren", SQ gold pin pentodes. D3a is mentioned before like possible good driver. C3g is a very interesting tube, too, inside and outside shields, loctal socket, low noise, linear. Nice triode - connected curves; with OP, say, Uak=182V/Ugk=-3V/Ia=12mA we`d have µ=40 and rp~2k6. Looking good for the (300B) driver, RIAA stage input tube, etc. Must try it soon and report.
But, 6 of 15 D3a was defective right from the box, white getter = air inside the tube through barely visible crack between the pins...
The best thing is, those quality tubes can be (still) found relatively cheap.
Some informations and pictures from the Web:

http://www.jacmusic.com/nos/C3g-C3m-info.html
http://www.tubecollection.de/ura/postroehren.htm
http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/Behoerden/Post/C3g.htm

And detailed "Telefunken" data:
http://frank.pocnet.net/sheets/128/c/C3g.pdf