Speaking of which, none of the tubes in that set had octal plugs and sockets. This seems to me a bit late to introduce a tube that wasn't octal, so obviously I don't know when octals were introduced!


I was skeptical, so I looked. According to the site you sent me to above, the 80 was introduced in the late twenties. Obviously this site has some lore as well as some facts. (EDIT: Later in the same description it indeed says it was introduced in 1936. The site names two dates of introduction.)


It sure is! it's an integral part of the power supply, a low-pass filter intended to pass the low low frequency called DC.

BUT since AC from the power supply is introduced into this coil, the magnetic field varied at the rate of 60 Hz (ok, ok, 25 to 60 cps) in it, which resulted in hum in the speaker. To counter that, a separate small coil was added to the speaker magnet assembly, and that was fed filament voltage that could be adjusted in the better amps.

So... we need a magnet; power supplies can use coils; the coil is a magnet but it has some hum; so some adjustable hum is introduced to counter that... and we wonder why it took so long to get high fidelity sound?


THAT explains its robustness, even its large surface area, which helps it be cooler than it might be!

I don't have the room for all those amps. My stuff for installation is almost overwhelming as it is. If I had the room, I'd have two cutting lathes, anyway....