[WallaceRoger]

If I'm right about the power supply in this set they may be connecting the battery tube filaments, in series with the cathode of the amplifier section of the 70L7 tube, it probably also has a dropping resistor in series with the heater of the 70L7 tube. I have one or two radios that work this way, it gives you much more audio power then the 3Q5 tube would.
Regards
Arran

Do you think the old A and B batteries are critical for normal operation? The power supply is tiny, which I'd expect for a portable model. Though it does have a switch for battery operation or standard AC. The battery leads are actually in nice shape, so I was planning on desoldering them from their junction and reusing the wire elsewhere.