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What is triple mica in 12AX7/5751 tubes
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Sal Brisindi
May 2, 2002, 10:15:00 AM5/2/02
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Can someone explain to me what is triple mica when referring to 12AX7's
and 5751 tubes. I assume its the top and bottom area that holds the
internal parts together. I have a bunch of the 5751's and wanted to know
how I can tell they are triple mica. The 5751's I have are black plates
also from looking at them. While I am at it, why are black plates
preferred to the other plates?
and 5751 tubes. I assume its the top and bottom area that holds the
internal parts together. I have a bunch of the 5751's and wanted to know
how I can tell they are triple mica. The 5751's I have are black plates
also from looking at them. While I am at it, why are black plates
preferred to the other plates?
Sorry for all these questions.
Regards,
Sal
Phil
May 2, 2002, 1:39:34 PM5/2/02
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Sal,
Triple mica's have two mica spacers about 1/4" apart near the top, and
a third spacer near the bottom. If I remember correctly, the middle and
bottom spacers actually have two spacers each, but they are right next
to each other, and so each pair makes up "one spacer."
I have no idea why BP's are preferred, unless they just sound better, but
I have never seen a grey plate triple mica, only black plate triple mica's.
Phil
S. Ono
May 2, 2002, 2:39:52 PM5/2/02
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The third mica sheet lies above the regular top mica spacer and serves to
isolate the cathode from possible contamination from the getter flash. some
European tubes, like Mullard and Telefunken have a smaller, very intricately
cut mica mounted on the regular top mica sheet so that it sort of spring
loads over the cathode for the same effect. The new 6550EH tubes also have a
third sheet, although JC Morrison says that it was more to eliminate
microphonics by mounting the structure more rigidly in the glass envelope.
isolate the cathode from possible contamination from the getter flash. some
European tubes, like Mullard and Telefunken have a smaller, very intricately
cut mica mounted on the regular top mica sheet so that it sort of spring
loads over the cathode for the same effect. The new 6550EH tubes also have a
third sheet, although JC Morrison says that it was more to eliminate
microphonics by mounting the structure more rigidly in the glass envelope.
Stu
Mikkel C. Simonsen
May 3, 2002, 7:41:44 AM5/3/02
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Sal Brisindi wrote:
>
> While I am at it, why are black plates
> preferred to the other plates?
>
> While I am at it, why are black plates
> preferred to the other plates?
I think the reason is that some good tubes have black plates. That has
made some people think that all tubes with black plates are something
special...
Best regards,
Mikkel C. Simonsen
>
> Regards,
> Sal
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