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Old 10th Jan 2020, 11:07 pm   #3
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: "Double anode" triodes/tetrodes.

The EF816 dual-anode pentode at least followed the precedent of the 6BU8, which was a joint development by Zenith and GE for used as a noise-gated sync separator and noise-gated AGC rectifier for TV receivers. This was chronicled in “Electronics” magazine 1957 May:

Electronics 195705 Noise Gating Tube for AGC and Sync.pdf

(This is a highly compressed .pdf, so of questionable readability. The original article is available here: https://www.americanradiohistory.com...aster_Page.htm,)

The back-story here starts with another Zenith-GE joint development of the 1940s, namely the 6BN6 gated beam valve intended for use as an FM quadrature demodulator. Zenith also used the 6BN6 as a TV sync separator, then as a noise-gated sync separator. It was expensive for the job, though, and the existing 6BE6 heptode was found to be suitable and adequate, although not quite as good. The steps from there to the 6BU8 are covered in the above article. Following Zenith’s deployment of the 6BE6 in the noise-gated sync separator role, the industry developed sharp cutoff heptodes that were better for the purpose, namely the 6AY6 and 6CS6. These were also slated for use as colour subcarrier demodulators. (And were used as mixers in some HF receivers.)

As an aside, whilst Zenith and GE had co-operated on some circuit and valve developments, and both were staunch supporters of FM during the late 1940s and 1950s, the Zenith-GE pilot-tone FM stereo system was not a joint effort. Each submitted its own system for evaluation by the NSRC and FCC; the FCC saw that they were very similar and combined them as a single system for evaluation purposes. Post facto there were apparently claims and counterclaims as to who had “really” invented the system. (There was an earlier thread about this: https://www.vintage-radio.net/forum/...d.php?p=803619.)

No doubt the 6BU8 and its successors such as the EF816 found several other uses. Mullard proposed the 6BU8 for use in a stereo decoder for its own TDM system detailed in Practical Wireless 1960 May, p.57ff.

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In contrast, Mullard’s early circuit for decoding of the Zenith-GE system used an ECH84 pair, or alternatively an EH90 (6CS6) pair.


Cheers,

Last edited by Synchrodyne; 10th Jan 2020 at 11:15 pm.
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