Found 2 12AT7 valves inside a Fender (Evil) Twin today.
Both branded 12AT7, National, made in USA.
Except one is way bigger than the other one.
The bigger one has a plate structure some 1.75 times taller than that of the smaller one, yet both are apparently 12AT7.
On my valve tester, the larger valve traces showed approximately twice the current of the smaller one. The curves basically look like this is a double current 12AT7.
What is it?
Gareth.
the
eIt is a 'mistake' - pure and simple, nothing exotic at all.
"National" as distinct from National Union (NU, later, Philco) was a rebran der of tubes, and once upon a time, the house brand for a number of retail tube sellers including Richardson Electronics. Much of their stock came fro m surplus, pulls and culls from the actual manufacturers and in point of-fa ct sold with no further testing than fitting in the appropriate box after r elabeling.
What you have is a tube getting mixed into a lot, scrubbed, painted and box ed, and sent off into the world with no further thought.
Peter Wieck Melrose Park, PA
**
Nothing to worry about, the shape and size of plate structures of common twin triodes vary a lot.
.... Phil
It is a 'mistake' - pure and simple, nothing exotic at all.
"National" as distinct from National Union (NU, later, Philco) was a rebrander of tubes, and once upon a time, the house brand for a number of retail tube sellers including Richardson Electronics. Much of their stock came from surplus, pulls and culls from the actual manufacturers and in point of-fact sold with no further testing than fitting in the appropriate box after relabeling.
What you have is a tube getting mixed into a lot, scrubbed, painted and boxed, and sent off into the world with no further thought.
Peter Wieck Melrose Park, PA
************************************That starts to make sense.
If I have a tube marked 12AT7 in a glass envelope much bigger than any
12A()7 I have ever seen, and that tube produces curves with double the current expected at all voltages/bias points, then that tube cannot be a 12AT7.I didn't know that about the National brand. Thanks.
Gareth.
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