You could just go on ebay and find a bench type power supply to use, that way you'd always be able to power up an old battery set regardless of whether it needs 67.5 or 90 volt "B" power.
Eico made a couple of models way-back-when that included 6.3 and 12.6 volt filament taps along with a 0-400 volt variable supply. I haven't looked lately, but I would venture to guess these are still around for a decent price.
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