Re: Hallicrafters S27
Yes, the S27 was designed to feed a 500-Ohm line as standard; that was sort-of commonplace as a way to distribute audio around a site in times-past (just as the "100-Volt" line is used nowadays).
A small transformer can be used to match the 500-Ohm output to a modern low-impedance speaker. It doesn't need to be a perfect impedance-transformation, the S27 has a push-pull output stage so there's plenty of 'oomph' on-tap to override any matching-indiscretions.
[This thread reminds me that I've got a S27 in my to-do pile; it's had the original output-transformer replaced by a modern one to match 8Ohm speakers and the S-meter zero pot moved so the new transformer can fit; since I'll only ever use it on headphones I'm minded to strip-out the bogus transformer, remove the two push-pull output-bottles and wire the headphones direct to the driver stage]
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