The most common battery-powered vacuum tube of the Reich

[Yuri D.]

Yes - we are talking about the RV2P800.

You will see this tube in many well known sets:

Torn. E. b,
Kw.E.a,
Lw.E.a,
Fu.H.E.c
SEG2T
Torn. Fu. d2
Torn. Fu. b1 - c - e - f - k
.
.
.
and many others

This is a battery powered Pentode:

Power requirements:

Fillament voltage: 2 Volt / 2 Amp
Anode voltage: 90 Volt / 0.2 Amp

There are no substitutes known for these tubes.

The RV2P800 is very sensitive to Fillament voltage variations, this is why you should NEVER apply power to a receiver with these tubes in place without testing the receiver first. It takes very little overcurrent to fry the fillament, leaving you with a dead, or highly degraded tube.

This tube is dated 12/28/42 - Stalingrad Winter

[Yuri D.]

Here you can see the tube name and "Wehrmachtseigentum" (property of the Wehrmacht) stamped on the tube's aluminum shield.

[Yuri D.]

The tube was made to be physically rugged and for easy battlefield replacement.

The "maker's mark" (TE-KA-DE)