In message , Scott Dorsey
writes
Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?

You can, but the tube filaments won't last as long because of the turn-on
surge. If it's a circuit where the tubes fail with poor emission long before
the filament fails, that's fine.
--scott

I don't get it. Maybe I'm a bit thick, but why would the turn-on surge
higher? Provided the filament current is the same for both tubes, I
wouldn't have thought that it would have made any difference. In the
good old days, I'm sure that I have connected up 12AX7/12AU7/12AT7
heaters (12.6V centre-tap) to run off 12.6V (pinout =
anode-grid-cathode-heater-heater-anode-grid cathode-heater CT). Would
the switch-on surge be less if they were run connected for 6.3V?
Ian.
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