Just picked up 10 nos mesa 12ax7's from the 80's

The SP tubes are very low noise. Mesa typically used those in the first input tube socket. They generally cost twice as much as the non-SP tubes.

I bet they are all chinese.

 

I think THD use those '80's tubes ( not labelled Mesa obviously) in their new shipments.

Pete.

 

"...how can I tell if I have the good chinese tubes?"

Plug 'em in and play 'em.

 

From Lord Valve's (Willy at NBS Electronics in Denver)... preamp tube catalog...

"NOS CHINESE 12AX7 GREY-PLATES

Along with my lucky score of "Silver Special" NOS Chinese
12AX7s, I also got ~500 pieces of the original "Beijing
production" Chinese 12AX7s. These are the same tubes that
all Mesa amps shipped with in the late 80s and all through
the 90s, and they were used in many Fenders, Marshalls,
Bogners, etc. Excellent for use in all guitar amps.

UPDATE 09/28/03 - I am finding a small but steady trickle
of these, at progressively higher prices. Still worth
the money.
EACH.......................................$15.00"

HTH
Slick51

 

There are "NOS" Chinese production that sound great. The grey plates are nice, the "silver specials" are simply fabulous. Particularly in old Fenders (to my ears anyhow...)

Here's what they look like:

http://www.wakarusaamp.com/misc_junk/technical/reference/tube_pix/index.html