Pietro Noto in Italy used to make a small inverter module that used a 6-volt sealed lead-acid battery to provide all the necessary voltages (3 volts for the valve filaments, -12V grid bias & +150V HT), but I'm not sure if he is still doing that.
You could take a 996 lantern battery apart and connect it in series/parallel for the 3-volt supply (that was the make-up of the original LT section, two pairs of 'F' cells in series/parallel), and 8 x AA cells in a holder for the grid bias section, but the 150 volts will always be a problem.
(I regret not buying some of those inverters when I had the opportunity.)
Chris.
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