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In Reply to: Need help identifying 12AX7 please (pic) posted by wpod on September 24, 2004 at 13:46:05:
Are there cross seams on the top of the tube? It looks like you have an Ei made tube, made in the 70s for RCA, the cross seams would be the final bit of evidence. They are very nice tubes IMHO, I've seen a number of them pass through here.
Follow Ups:
Jim did you get my emails re the NOS orphan Kt90? Ive sent a few......maybe I have a bad email addy?
(nt)
Cheers, EveAnna Manley
Hey, what does a GIRL know about tubes? (hint - in this case, a LOT!!)Thanks for the confirmation EveAnna - oh great tube Goddess of the American desert.
Actually, other than my lousy humor, I was wondering if you had any insight as to what's happened to/at Ei? The current stuff is just so poor quality, and they made so many excellent tubes in the past...
It's not just Ei... tubes just ain't what they used to be...It's Friday nite and tubes have been driving me crazy all week. I'm going home now to watch my TiVo on my solid state television (10 year old Sony Trinitron-- its picture tube is still plenty fine... I think.)
Cheers, EveAnna Manley
Hey-Hey!!!,
The excellent performance of the KT90 and its recent failure to meet ratings has led me into wondering just what is wrong with it. Has anybody taken apart a good one and a bad one and measured it( to half or quarter mil tolerances? ) I have my suspicions about what might have gone wrong but it is only a suspicion.
regards,
Douglas
!
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
The screens are misaligned, I've posted this before. Because the screen is misaligned one section of the cathode and plate carry more of the load than the rest. This causes the localized overheating and the red plate.
Hey Jim,
I have read your posts on the subject. What I am curious about is the nature of this misalignment. As in what is causing the misalignment, and in what direction? radial, axial, some combo?Did they change their mica dies at about the same time this cropped up?
live long and prosper,
Douglas
!
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
Hi Doug,"What I am curious about is the nature of this misalignment. As in what is causing the misalignment, and in what direction? radial, axial, some combo?"
Beats the s**t out of me. I just don't know, and without precision measuring equipment I don't know how I could even tell.
I'm sure the cause is poor assembly, the reason for the poor assembly isn't known to me. I don't see any difference in the mica, although it wouldn't take much to get it out of line. If they changed it I don't know about it. But that's not saying they didn't.
The red plate isn't nearly as scary as looking inside the tube and seeing so many turns on the screen winding glowing white!
This is the same thing that happened when the then Svetlana (now SED) 6550 first came out. In fact, speaking with Eric Barbour he informed me that the plate holes in the later 6550 tubes were designed to allow use of a special tool specifically for alignment of the screen. Once the tool came into use the red spots on the tube disappeared.
And if the KT-90 was the only Ei tube that went in the toilet quality-wise, you might think it was something unique to that tube. But all the Ei stuff went bad it seems (to a greater or lesser degree).
I wish I could tell you more, but I'm at the limit of my tube manufacturing process knowledge.
If the damn EH KT-90 sounded good I wouldn't care, but it sounds lousy. Certainly nowhere near the Ei.
[]===== < ~~~~~~~~!
so can we get some measurements, or some good and bad tubes to measure. Not that thicker plates ever hurt anybody, but I don't think the Type III troubles reported by Jim McShane are from that sort of a change.
regards,
Douglas
Beware the man who behaves deceitfully towards others, for there is nothing else to save you from his deceiving you
two of them (opposed) are like a raised 1/4 inch long ridge that extend from the top (1/4 in from tip) curving over the edge of the glass while the other two that are perpendicular to these are barely distinguishable. I tried to take a photo but its fruitless. Did Ei use etched codes like the ones that I mentioned above? Thanks again, wpod
Yes, the seams and the code coupled with the flat smooth plates and the RCA labeling all point to Ei.
Jim,Are you saying that 'cross seams' at the top of the tube mean they ARE Mullard or ARE NOT Mullard?
Crossed seams appear on Amperex, Ei, and Japanese 12AX7s. A single seam appears on Mullards.
nt
the flat (not ribbed) plates indicate they are not Mullards.
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