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Old 1st Dec 2017, 12:54 am   #26
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Vintage Television Technology.

Some comments on the UHF tuner noise issue were provided in Fink (1).

Of conventional UHF triodes, it was said that they did not compete with a crystal mixer if the first IF stage were designed for low-noise.

Comparatively expensive disk-seal and pencil triodes competed with the crystal mixer, and some very costly types outperformed it.

A noise figure of 10 dB was claimed for well-adjusted UHF tuners employing crystal mixers. I suspect that this was a best case, with typical numbers running somewhat higher at the top end of the UHF band.

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A graph showing the comparative noise figured for the various UHF triodes was also presented:

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It’s a pity that we don’t have similar curves for the PC86 and PC88.


Against that, an early (1953) UHF tuner by Tarzian and used by Sylvania was something of an outlier:

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It had no RF amplifier, but used a 6AN6 as a grounded grid mixer, fed by a 6AF4 oscillator.


Cheers,



(1) Donald G. Fink, Editor-in-Chief; Television Engineering Handbook; McGraw-Hill, 1957; LCC 55-11564.
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