I am looking for a nice schematic, and perhaps additional info, on a 12V
(fil. & plate) tube superhet Rx; just something fairly simple for CW/SSB
reception without bells and whistles, and preferably for 75M/40M reception.

Can anyone point me to info on this? Thanks.

Operating tube plates down to 12 VDC supply is pushing things a
bit far, to be honest with you.

Setchell-Carlson managed to do it with loctal-base tubes running
off of a 24/28 VDC aircraft bus back in WW2 times. No dynamotor,
just that cute little box referred to as a "range receiver" or
BC-1206.

I bought a couple of them many years ago, surplus, principally
to get the nice compact 3-gang variable capacitor. Fired one
up in the company lab at 26 VDC and it was still in-spec although
those specs weren't the best. At 24 VDC the spec rating was
marginal. At 22 VDC it was below spec...but then the filaments
were also running cooler at 11 V each.

Don't remember what the IF (135 KHz) BW was, but, running with
a crystal-controlled converter ahead of it, the 195 to 500 KHz
tuning range could cover 75 or 40 meters no problem. A thought.