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Shopping for unfamiliar tube types

Posted by Bambi B on February 27, 2007 at 11:47:36:
hartwerger,
Yes, I'd never heard of the 12SC7 until your thread. I assume though that if Mapletree uses these in their current phono preamps, there must be a lot of these around. A quick glance at Ebay shows them to be around in good numbers, and whatever function they serve, they're remarkably inexpensive- someone is offering 50 for $49.99 !
It is possible to get good results while buying tubes without previous knowledge or specific recommendations- you just have to buy a few more. This is not as painful when the tubes are $3. as opposed to needing piles of 7308s at $120 each. I needed to buy a number of tube types I'd no experience with- tuner types for a McIntosh MR67 and since these less used types are cheap, I was able to buy a number of versions sight unheard as it were, by simply looking for brands, construction features, and test results that made sense to be high quality. I bought Valvo, RCA, Telefunken, Siemens, and Sylvania Gold Brand and looked for the premium version with the oldest construction I could find- black plate, D- getters and only if they wre tested at NOS levels. With the low prices I was able to buy, for example, 6AB4s that were Bugle Boys, Telefunkens, Siemens, RCA at a nvaerage price of about $4 each NOS and tested. It takes a bit of poking around, but you can also find interesting things that are sort of hiding in plain sight- rebranded tubes can be "sleepers" . I bought Siemens E80CF/7643 (the premium, gold pin 6BL8) and these $5 tubes turned out to to be relabelled Telefunkens identical to the ones I'd just paid $22 each for- just a different name and box. Along this line, I noticed on Ebay there's a 12SC7 offered that is labelled and boxed "Rogers"- and Rogers tubes are often Dutch Amperex. -It's worth probing a bit when something pops up. I bought 10 generically relabelled 6CG7s that turned out to be unusual black plate, D-getter Hitachis for $3 each- quite like early black plate RCAs.
Also, it's worth seeing if there is a European equivalent number for these and then if there's a Euro premium version. And, though I don't know the 12SC7, it just seems that RCA would have made good ones.
It's interesting that the 12SC7 are metal tubes, looking like early, smaller 6L6s, and these seem to be from the late 40's, early 50's.
With the unfamilar types I always check for a later or premium version that might also have a higher currrent rating- similar to the changes to the 6L6 where the "GC" is much more robust. With the 12SC7, there was apparently the "1634" as a premium version and Tube World has a few NOS RCA of those at $10 each. I would also look into whether there was any other military version, and I'd try those as well- more rugged and higher current handling usually.
You might also ask Mapletree for allowable substitutes- perhaps there's a super-duper version- or 12SN7s or something- that they would have liked to use but couldn't buy in sufficient quantities for production use.
Always interesting to see an unfamiliar type pop up. I would though consider how long it's been since this type was made and perhaps build a small stock of carefully selected ones- it there are no substitutes, I'd buy a 30 year's supply!

Cheers,
Bambi B