[VintagePC]

Found an ebay seller with a large variety of NOS tubes and a free shipping promo for over 20 items. I stocked up and got everything I need for about a dollar each except a spare 5u4 and some 6sn7s.

Looked closer at my 1B3, getter is completely gone, so it's totally gone to air. No obvious cracks.

Electronic M - In retrospect, I'm intrigued by your comment... One would think sets would be designed so that typical failure of any arbitrary tube would result in minimal or no damage. What is it about the circuit design that makes the HO tube red-plate if there is no oscillator? Are there other parts of the circuit that are similarly affected if another single tube fails?

Granted, in a typical case I would assume tubes wear out rather than failing abruptly and a weak oscillator would get replaced before it reached that state, but I can imagine it certainly wouldn't be uncommon for a tube to sometimes go poof from thermal stresses or filament burnout.