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20 Watt SE. I had found it.
20 Watt SE. I had found it.
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Old 9th April 2006, 09:46 PM   #11
Ryssen is offline Ryssen  Sweden
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It seems that they using a 211 to drive the output tube (also 211).
I think it isnīt 211 as the driver,have a look at the driver it has a katod-the 211 has no "katod" as it is direct heated,it is written just under the driver 5687WA,so the 211WA over the driver must be some missprint or sommething.
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Old 10th April 2006, 08:39 AM   #12
Hojvaelde is offline Hojvaelde  Denmark
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I got a better schematic and there was only one 211/canal

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Old 10th April 2006, 09:04 AM   #13
schiller is offline schiller  Greece
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This is the well known shematic with the 5687 cathode follower, which, i repeat, doesn't work properly, unless you parallel 2 systems of the tube. Bei +20v at the grid the 211 draws 8mA current, which is the idle current of the 5687 follower. You need at least twice that value, otherwise the distortion near full power (in this case above 15w) will be severe.

I firmly believe that the original ongaku does use 2 sections 5687 in parallel cathode follower as driver.

According to the datasheet, you can get about 20w from an 211 in A1, biasing it at 100% plate dissipation (1200v/ 60mA). I wouldn't do it, it shortens tube life unnecesarily.

I think you are doing well, asking in the forum, not all shematics on the web are correct. A lot better is, by such elementary things (tube operatin in class A), if you can judge for yourself.

Good luck with your project
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