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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: Made in America posted by kentaja@yahoo.com on March 17, 2005 at 12:23:22:
On the history of the 6DJ8 and 6FW8: sponsorship of EIA registration of the 6DJ8 was by Rogers Electronics (Canada), presumably as an agent of Philips, and final registration was released in May 1958. RCA sponsored the 6FW8, released June 1959.Both were "hot" frame-grid types for cascode TV tuners. Their Gm was effectively the same (6DJ8: 12.5 mA; 6FW8: 13 mS) and their noise performance was probably about the same. It was intended for low-noise RF amplifiers. "Hot" meaning high performance in a typical (usually cascode) amplifier circuit. Like the 6DJ8, it was not intended for audio applications originally. In triodes in general, high Gm => low noise. Frame-grid tubes use a rigid four-sided frame on which the grid wire is wound, rather like a harp. This allows the use of very fine wire, rigidly supported and tensioned, unusually close to the cathode. So unusually high Gm is possible. This was a Western Electric innovation of the late '40s which got adopted by some European makers of high-performance tubes (Siemens et al.) and which came back to the U. S. via Philips' Amperex. Amperex had a strong position in frame-grid mass-market tubes (6EJ7 et al.). The 6FW8 was probably RCA's first frame-grid product; who knows, maybe they didn't market it vigorously out of fear of getting into difficulty with production. The whole magic of the frame grid is that it makes tight tolerances achievable! Any tube that got out of the factory will probably serve you well.
6FW8 was a "Harrison" type (developed by RCA in-house engineering staff), as opposed to RCA's other plants at Cincinnati, etc. It was not promoted aggressively to the industry, instead being restricted to RCA's TV division and to the replacement market. Initial production forecast was 70,000 tubes per year, a rather small rate for RCA. In calling it a "Harrison" type, I meant production at Harrison, not Woodbridge (NJ) or the other RCA plants of the day. "Competing types" at the time were given as the 6ER5, 6BQ7A, 6ES8, and 6DJ8.
As of 1961, the 6DJ8 was offered by (only) Amperex, Sylvania, and Westinghouse. List price was $4.25. The 6FW8 was offered by RCA and Westinghouse. Price was pretty steep, at $9.20 (in old dollars). If the permanent markings are surrounded by a little box, it's RCA (or in some cases, Tung-Sol). If surrounded by large dots, the tube was made by Westinghouse. I can’t find catalog evidence of anyone else offering them besides Westinghouse… and because Westinghouse had an extraordinarily wide line of types for the replacement market, they were probably selling RCA-made tubes. Canadian manufacture is possible but not too likely. Rogers, as sponsor of the 6DJ8, probably wouldn't have been interested. Canadian Westinghouse or Canadian GE might have been put off by the small size of the forecasted demand.
I'd guess that RCA felt they needed a home-grown version of the 6DJ8, but didn't want to promote the thing strongly because their Nuvistor tube—an even better deal performance-wise—was coming out at the same time. The history of the tube business is full of multiple products from competing makers that did the same job.
I notice that the SAMS substitution guide, which tends to be pretty timid otherwise, encourages one to substitute the 6DJ8, 6ES8, 6KN8, or 6R-HH8 for the 6FW8. Maybe the last three also have potential as affordable 6DJ8 replacements!
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Follow Ups
- History of the 6DJ8 and 6FW8 - 6SN7GT 17:41:30 03/17/05 (2)
- Re: History of the 6DJ8 and 6FW8 - kentaja@yahoo.com 10:00:54 03/18/05 (1)
- Re: History of the 6DJ8 and 6FW8 - 6SN7GT 03:25:19 03/19/05 (0)
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