[Boatanchors] 6SG7 Question

[Peter Worrall]

I bought 10 6SG7s from a UK dealer who was closing down, a few years ago.

 I put them away with my other AR88 Spares, waiting for the right day to do 
a restoration job.

That day was last Saturday.

On closer examination of the 6SG7s, I noticed they all had production date 
stamps June 1982 ..............yes 1982.

Can any one tell me why 6SG7s would be still being produced 40 years after 
the AR88 was designed?

Pete