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In Reply to: Tektronix Selected 12AT7 on Ebay posted by rohrenman on March 20, 2007 at 17:21:34:
rohreman,As Tektronix used tubes in their instrumentation, their tubes had to be highly selected and Tektronix used the best tubes at the time. Note , the seller is including the curve trace test results which is a more comprehensive sign of their performance than a transmutual conductance test as it covers the tube over it's whole range.
I have several NOS Tektronix tubes including a box of 4- RCA "cleartop" 12AU7/ECC82 that the test results show are matched within 2% of all 8 triode sections. The ECC88 Tektronix are orange globe label Amperex. This is the first time I've seen Tektronix as Sylvanias, but depending on the era and construction, the 12AT7 was the tube that I think Sylvania really got right. it's a pity the seller shows the tube from a mile away anf the label covering everything- there's more interest in the testing than the tube! Personally, I would ask for photos that show the tube's construction, though it's likely it will be the oridinary two mica grey plate. I woul dbe more excited aobut these if they were not the Sylvania green printing and were the older, gold printing.
The Sylvania 12AT7/ECC81 is a lush and deep tube that may or may not suit vintage gear that is warm or soft, but in modern gear might help tame a bright preamp. I use mid-late 50's triple mica,black plate square getter Sylvania 12AT7WAs in my microphone preamp that are quite incredible. By the way, these Sylvanias are common and not expensive- I bought 6 of these 50's ones recently for $6 each NOS, but the testing should give confidence if you need preamp tubes that have closely matched sections and are low noise and microphonics.
You can depend on Hewlett-Packard tubes as well being super tested and usually good brands- I have acouple of super H-P 12AU7/ECC82 that are early 60's Amperex indistinguishable from the Bugle Boy.
Cheers,
Follow Ups:
Now they have an "E" under the 12AT7 marking, I have seen "WA" and "W" under the 12AT7 markings but never an "E" do you know what this is about?
'As Tektronix used tubes in their instrumentation, their tubes had to be highly selected and Tektronix used the best tubes at the time.'This is incorrect !!! Tektronix used to specially test the valves to work correctly in their equipment rather than selecting 'the best at the time' .
cheers
Tektronix tube scopes have exceptionally long service lives, obviously great care was taken in selecting all parts that went into them, not only the tubes. Ahh.. those were the days
Hi ,
I always like the little roll of silver solder inside those old scopes and the dual beam CRT :) These days to keep an old Tek scope going would cost a fortune in 6DJ8 though .cheers
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