Two 12ax7's, both salvaged from old audio equipment: (1) All printed markings have rubbed off, the number '15' is pressed into the glass at the base. (2) All printed markings have rubbed off, no number is pressed into base. thanks
Those look like Philips-style construction, and they're likely to have etched codes on the bottom side of the glass. When you say the marks are pressed in the base, are you talking about the bottom, between the pins? Philips codes are on the lower part of the glass side. Here's a link for reference: Philips tube codes. - Thom
Yes, in the circle that the center of the base between the pins. I didn't notice at first but the top one has 'B8B' etched faintly into the side near the bottom. This one also has white print on the sides that has become illegible. The bottom one, I can't see any etching, but it had white and red print on the sides that has become illegible.
Those "open" semi circular vent holes (as opposed to blocked by the shiney "sandwiched" metal between the plates) make me think "Japanese, Mullard knock off".
Doesn't show in the photos, but the top tube has the shiney metal layer blocking the semi-circular holes. The bottom one, you can see the edge of a shiney layer but it doesn't block the holes. Does that mean the top one is a mullard, and bottom is a japanese mullard copy? I have a couple other old mullards that look similar but the plates are a little longer.
That would be my best guess. There was a long plate variation of the Mullard as well. Etched codes, or lack thereof, would be the final indicator of a Mullard or Philips tube.
The top one is a Mullard, then, made in 1968. Try using a jeweler's loupe on the bottom one, under strong light; you may discover a code, if there is one. I'm not inclined to i.d. the second one as Matsushita - all Matsushita I have seen have the round getter wire set at a conspicuous angle, instead of roughly parallel to the mica disks. - Thom
I hadn't known that the "see through" holes were a feature unique to Matsushita. The holes do seem large, but it could be an artifact of the photo angles. The largest of such holes I've seen belong to Tungsram tubes, but those are easy to i.d. by the square metal tag on the getter support, and the fact that there are two getter supports. I don't have any Matsushita 12AX7, but I do have their EL84, and they have the "n" Philips code on them. Matsushita was part of the Philips conglomerate. - Thom
I'm not certain that this is unique to Matsushita either, only that those are the only ones I remember seeing with this feature. I also don't recall seeing Philips like codes on them, but that could be a problem with either my eyesight or memory.
Yeah I have some no etch code mullards look alikes with the see thru holes going thru them. Curious of thier actual origin myself. I dont consider them real mullards or Matsushitas. Red RCA labels...FWIW Bob
