Any common subs for a 12c5?

[David Roper]

What matters in a series string is that all the tube filaments draw the same current. a six volt difference in the string can more or less be absorbed, but in order to drop a 450ma-heatered 6AQ5 into a 600ma filament string you'd have to put a resistor across its heater to lower the resistance between pins 3 and 4 to 10.5 ohms. Across--as in parallel, not series. Then the string thinks its seeing a 6-volt, 600ma tube. Easy as scrambling the rest of the connections, but obviously doesn't even speak to the match of the tube to the OPT etc. A really, really squirrely quick solution to the problem when the only problem is the wait.