I picked up a pair of CK647 tubes at a local military surplus place, as they looked like dual triodes and were cheap. They look like a tall 12AX7, and after some testing with multimeter and tube tester, appeared indeed to be function as dual triode with same pinout as 12AX7 and other similar 9 pin dual triodes. So I went out on a limb and put one in an amp in place of a 12AX7 and it sounded great, maybe a tad less gain than a 12AX7 but louder than a 12AU7, and great tone. I couldn't find any specs on this tube on any of the standard internet tube data sites, so does anyone have any information on this tube?
Well, I checked my "Armed Forces Cross-Index of Electron Tube Types And Allied Devices" (1952) and yours wasn't in there. That's a 370 page manual with a butt load of numbers. However, from your description of a CK647 it seems like it might a 12BZ7 which is a hi mu dual triode similar to a 12AX7 with a lower plate resistance.
Thanks for the reply, I should have mentioned it was made by Raytheon, if that helps any, but online search didn't turn up any data on the tube.
Yes the prefix CK was used for early Raytheon tubes. And it's not uncommon for tubes to have two or sometimes even three numbers.
I looked all over and was surprised at not being able to find anything even on Frank's. I thought I had a Raytheon tube manual somewhere in my very neglected book collection, but if I do I was not able to find it.
Not in the 1963 Mil Handbook 213A. Sibley's Tube Lore says "duotriode like 12BH7, no other identification" Could also be like 6414 or 6829, which Raytheon also made, a bit higher; same 12A/B*7 footprint.