Re: Wanting to build a higher powered SE.

Postby EWBrown » Sun May 19, 2013 12:01 pm

    My OPT has 36 ohm of 3rd winding coil which adapted to 838(Mu of 50) and gets dumping factor of 1.6 with only CFB.



Just watch out for that "dumping factor", it will get you every time! ;) :)) (lol) O:)

/ed B
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Re: Wanting to build a higher powered SE.

Postby EWBrown » Sun May 19, 2013 12:09 pm
Update 8/10/16: Gary Kaufman's website on the-planet no longer exists, the server had a fatal crash several months ago,
and all that wonderful tube data has vanished =:o :'(

Nov 25, 2016: Note: some of his website has been partially restored, the info in "Links" is still valid, it has been adjusted to work with the restored files.

However I managed to save the schematic and a couple of photos of the completed amplifier, well before the crash, so I can e-mail it if anyone wants it.

Gary Kaufman had another Nobiru Shishido (sp?) SET design on his website, using an 826, driven by a 6EM7, with a Class B interstage transformer feeding the 826, which, in order to run in Class A2, requires a positive grid bias voltage of approx. 40 VDC. It does draw significant grid current, and a Hammond 124B won't cut the mustard here... :'(

Note that the driver section is a more or less conventional 6EM7 SET design, so it furnishes 1.5 to 2W of drive in order to feed the somewhat power-hungry Class A2 826 grids.

Image Image

Image

Zoom in (real dimensions: 837 x 631)Image

I've seen and heard this one in person, several years ago. It is not very high powered, maybe 8 or 10 watts, but its design takes a different approach.
Basic info: B+ 260V, 826: VP = 250V, IP = 115 mA; 6EM7 consumes 35 mA total. For a stereo amp, 260VDC @ at least 300 mA continuous, which is easy to
produce with an isolation tranny with a FW voltage doubler, or a 120:240 step-up and a FWB.


826 data here: http://frank.pocnet.net/sheets/049/8/826.pdf

826 fits the common "Septar" socket, about same physical envelope size as the Russian 6C33C. Filaments are power-hungry, 7.5V @ 4 A (eat) *)
And they really need to have DC power to eliminate any 60 Hz hummm issues.

The 826 was intended a moderately high gain (mu of 31) Class C RF oscillator / Power amp, so it has to be "tricked" into behaving as a Class A2 device. *) (y)


/ed B