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Old 23rd February 2003, 10:01 AM   #1
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Default sunday daydreamin'

Hi all

I'm just daydreaming here,
813 813 SE

Any comments?
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Old 23rd February 2003, 06:11 PM   #2
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Slo Mo,

I'd love to hear what that amp sounded like. Go ahead and build it and let us know.

The big problems I see with it though, is that the 813 has a mu of about 8 in triode, so you're going to need at least 9Vpeak of drive to the grid of the first tube to drive the second one to full power providing it's giving it's full gain, which it won't be. I'd either choke or CCS load or IT couple the driver tube to allow you to get some current through it, and still have a somewhat sensible power supply voltage. I've not tried the 813 at low voltage, but I suspect it could sound pretty ordinary at low voltage and low anode current, but that's something you'd have to determine by experiement. But you'll still need a grunty medium gain stage at the front, like a 6BX7 or a 12B4A running hot.

Otherwise, it's sort of Sakuma-ish.
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Old 23rd February 2003, 06:18 PM   #3
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Default I like high voltage valves!

Hi,

Bas Horneman's 813 page is well worth a perusal:
http://home.zonnet.nl/horneman/

Cheers,
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Old 23rd February 2003, 06:20 PM   #4
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Umm... use the 1st in pentode mode instead?

an IST would allow some grid current, partially making up for the poor performance of triode mode (as compared to tetrode). Adjust load accordingly, of course.

Tim
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Old 23rd February 2003, 06:24 PM   #5
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Quote:
Originally posted by Sch3mat1c
partially making up for the poor performance of triode mode (as compared to tetrode).
I'm not sure what you mean here.
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Old 23rd February 2003, 06:27 PM   #6
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For instance:
6L6GC is rated for up to 10.5W in SEP (at 12% THD of course ).
In triode, it goes to 1.6 or 2W (I forget).

If you look at the curves, it is plain to see that plate current simply can't go nearly as high without grid current, in triode as compared to pentode.

Tim
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Old 23rd February 2003, 08:35 PM   #7
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Thanks for the comments , guys,

I was originally going to draw up the schem for my 10 - 813 SE
amp, when it occured to me that this would be a fun alternative.
This one is much simpler than my 10-813 SE amp, though.

Let's see, if we draw 55mA through the 1st 813 , it should get a
voltage gain of 6 and a bit , so the preamp would need to give
about 30V p-p, my 10Y-300b breadboard pre should do that.

Dont know how the 813 sound at these low voltages, though,
maybe an 845 would be better?
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