What's the difference between a 0-1a and a 01-aa tube? What types of radios were the 01aa tubes used for?
Were they for the smaller less output radios?

According to Radiomuseum.org, "The 01A has a thoriated tungsten filament. The 01AA has an oxide coated filament."

Oxide-coated filaments emit electrons better at low power levels, but thoriated tungsten filaments provide a longer service life. For a typical home radio receiver, the service life parameter would probably be the one of most interest to a consumer, since the tubes probably aren't going to be operated on the bleeding edge of their performance curve.

:According to Radiomuseum.org, "The 01A has a thoriated tungsten filament. The 01AA has an oxide coated filament."
:
:Oxide-coated filaments emit electrons better at low power levels, but thoriated tungsten filaments provide a longer service life. For a typical home radio receiver, the service life parameter would probably be the one of most interest to a consumer, since the tubes probably aren't going to be operated on the bleeding edge of their performance curve.

thanks, CV

Tubes with thoriated filaments, like the 01a, can be rejuvenated by heating them at several volts over rated in a tube tester. The extra heat boils the radioactive thorium up toward the surface. The emission is restored to essentially like-new after a few hours. I don't mind buying "weak" 01a tubes, ideally at a reduced price.