I know at least one person sells a dc/dc converter for Transoceanics
that takes 9 DC cells (+ 1 for the dial light) but they want 90 bucks
for it plus what ever the shipping charge is.
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A good reason to build such a converter yourself....probably for
peanuts. A 555 IC ,2 power transistors and a few passive components
Google is your friend. After all this is THE homebrew NG.

Good Luck

Frank KN6WH / GM0CSZ