71A Circuit?

[jmv]

I can't find the thread atm, but I recall that Paul Joppa recently posted about using the 71A tube in a battery-powered circuit.  Apparently they were common on old farm radios and ran off a 6 volt battery.  I happen to have a couple of 71As lying around, and I'll like to try them in a battery-operated setup.   Anybody have any insights here, or a place on the web you could point me to?

[xcortes]

The filaments are 5v low current and meant to be run off batteries. IIRC the datasheet OP for 750mW is 180v p-c, 40 v bias and 20mA so you can use batteries but many of them.