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Questions about tubes and gear that glows. FAQ

Re: I can replace a 7355 tube with a 7591 without modifications ???

The A500 may not be as easy to rebias as some amps. The filament voltages for V1/2/3 are obtained from the bias current (sort of a free source of clean DC). If you change the bias you may also have to rework the filament circuit.

My guess is that the extra .4A of filament current for 5881's might be less of a problem to deal with. Personally I'd probably re-pin the output sockets for 5881's. The transformer probably won't mind the small extra load - or you could add a small additional filament transformer.

If you need the schematic let me know.



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