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

• Kevins Garage

I've mostly played around with the EF86, making two triode-connected EF86 preamps. Very detailed sound, yet not overly harsh or bright. I'm building a new one (once the metal work gets in) for someone else using onboard regulation, chokes, etc...

I've also become interested in the EF40, EF12 and want to start using them. I also had some good sound out of a SE 300B amp using an SV83/EL84 - that was a budget version of a Loesch design.

• Kevin's Garage

Probably you know this, but besides many old tube books on-line, there is a big pentode test on Pete Millett`s DIY pages.
I like those cheap and "odd" tubes...

• http://www.pmillett.com/

anyways - I'm looking forward to getting some c3g and d3a tubes