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Post subject: Re: Bias Creep
Posted: Thu May 12, 2016 1:38 am
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Eroot64 wrote:
I think as far as the tube thing goes , the closer the plates get to a black body the more efficient the tube will be.


That's the conventional wisdom (which I also happen to subscribe to). That said, I have plenty of vintage gray-plate bottles from GE, Westinghouse, Tung-Sol, CBS-Hytron, and others that are fine tubes in their own right. Thus, I think it's important to not get wrapped around the axle chasing glass that may or may not even sound all that great.

Just sayin......

Arjay

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Post subject: Re: Bias Creep
Posted: Thu May 12, 2016 6:09 am
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Eroot64 wrote:
TimsAudio wrote:
There is another ambiguity that I'm confronted with in the percentages of black-body radiation, as well as the one you described. Are they only talking about thermal characteristics? Or does that relate in some way to the electrical emissivity and plate heating? My tube mysteries continue...

My Understanding is that a perfect black body (an object the absorbs and emits all wavelengths of EMR) is a theoretical model used as a constant in assessing how a material deals with EMR . Objects that come close to the constant are considered good transmitters. Its been a while since I studied all this planks law stuff, and the math is waaay over my head. I think as far as the tube thing goes , the closer the plates get to a black body the more efficient the tube will be.

.
My theory is that power tubes using black plates to dissipate heat ALSO absorb heat from the adjacent power tube's black plate. Therefore it seems possible that a gray plate power tube (being cooled by adequate normal convection) absorbs less heat from it's counterpart.
With black plates achieving a minor dissipation of heat compared to normal glass envelope dissipation,. maybe gray plates actually stay cooler.


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Post subject: Re: Bias Creep
Posted: Thu May 12, 2016 9:59 am
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You're right in that is difficult to find NOS power tubes for comparison.
I have studied preamp tubes though. The most prolific these days are the JJ ECC83 and it's various versions.
The differences in JJ tubes is readily apparent. Besides the gold pins on a premium JJ ECC83, the tube is noted for low noise.
Comparing the coatings, the gold pin version has different color coatings. The premium version is more likely to have surface cracks in the coatings than the base model. I'm not sure if it's a thickness difference or a formulation difference
I have also seen differences from the base JJ in the GT versions. The tube pins aren't plated and the color of the coating is slightly different.
It sets me wondering if all JJ tubes are created equal or if JJ will manufacture anything you want. I've seen JJs with a Telefunken badge that have very dark coatings. These, I'm sure have excelent performance, but I imagine some buyers are out to save money and order 10,000 stripped down models instead.


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