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Old 26th August 2008, 11:36 AM   #11
Tweeker is offline Tweeker  United States
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807s are not popular with modern manufacturers due to the top anode cap, a safety issue. The top anode does give better insulation making them well suited to transmitter roles though.
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Old 26th August 2008, 12:36 PM   #12
sarrisk is offline sarrisk  Greece
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For those who like to build a pair of PSE 807's here is the schematic (high resolution) from my project. : http://sarris.info/main/en/pset807


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costas

(meet me at my DIY web page : http://sarris.info )
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Old 26th August 2008, 08:47 PM   #13
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Quote:
Originally posted by sarrisk
Don't forget that 807 is a classic power output tube designed for transmitters...
The 807 is a 6L6 in a different bottle. At the time, RF designers still liked the old style 5-pin base, as opposed to the newer octal. Same internals, same specs, but the 807 has a higher voltage rating due to the top cap plate connection that won't work with the 6L6 (socket pin-to-pin flashover) and it's a good deal more convenient in that you can build your output circuits on top of the chassis, and the input circuitry beneath it. That doesn't really matter since the best audio Q-Points occur at the lower plate voltages anyway.

Doesn't matter what it was originally designed for. The 1624 was originally designed as an RF final for mobile xmtrs, but it also has some brag-worthy audio specs: THD= 2.0%, and better than a whole bunch of audio finals. Same deal with 6BQ6GTB horizontal derflection PAs: those sound as good as any of the best audio pents.

Quote:
It is difficult to make a design using this tube as an AF output. ( these designs suffer from noise produced by heaters, or from a careless design in power supply... ). Using of chocks or interstage transformers solve these problems but increases cost ( e.g WAVAC) and make the whole construction more complicated.
I think that this is the reason that remain "undiscovered.."
Not really. You just have to work within its limitations. Since the 807/6L6 likes to make higher order harmonics, you need to add some local NFB to linearize it. The developer of the type, O. Schade, recognized this, and recommended feeding back 10% of the plate voltage to the grids. I followed that recommendation when doing an 807 design, and he definitely knew what he was talking about. Include active screen voltage regulation and they sound just fabulous.
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Old 28th August 2008, 08:04 PM   #14
sarrisk is offline sarrisk  Greece
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Quote:
Originally posted by Miles Prower

Not really. You just have to work within its limitations. Since the 807/6L6 likes to make higher order harmonics, you need to add some local NFB to linearize it. The developer of the type, O. Schade, recognized this, and recommended feeding back 10% of the plate voltage to the grids. I followed that recommendation when doing an 807 design, and he definitely knew what he was talking about. Include active screen voltage regulation and they sound just fabulous.
Sure. That was i meant saying "careless psu design.." . I heard about NFB but i didn't knew the exact percent of feedback ! Thanks for the ifno !

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(meet me at my DIY web page : http://sarris.info )
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