[Boatanchors] Re: Tube substitution question

[krk@ix.netcom.com]

  I just got back from AES where I picked up a 5963 tube as a substitute for a 12AU7. 
At least I thought it was a substitute. My Eico 667 tube tester lists different settings 
for both types. Tested as a 5963, it comes out fair. Tested as a 12AU7, it comes out 
much better. It's going in an HQ-180A as the product detector. Anyone know just 
what the difference is between these two types? My memory (yeah right), tells me 
that the numbered tubes were heavy duty industrial equivalents of the number-letter 
tubes. True?

Thanks,
Ken kb7rgg