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Old 15th July 2011, 03:25 PM   #1
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Default 2SK82 + Lightbulbs = Fun

This is my first go at a 2SK82 lightbulb amp.

Nelson, are you willing to sanity-check my graph before I embarrass myself too badly?

Thank you,

Mike
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Old 15th July 2011, 03:47 PM   #2
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That's a lot better than I got:

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Old 15th July 2011, 04:18 PM   #3
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Probably I should add that I was concerned about the dissipation. As far
as I can tell, Sony didn't offer curves showing instantaneous dissipation
beyond about 80-90 watts, and they had a similar chip rated at 65 watts.

Out of concern for reliability, I didn't push it beyond 1/2 that.

If I read your data correctly, you are at about 100 watts dissipation on yours,
and I would certainly expect better numbers from that, but in addition I think
you've found the "sweet spot".

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Old 15th July 2011, 05:49 PM   #4
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I don't have the output centered. I'm at 17.5 Vds for around 50W dissapation. The rest is across the bulbs, and I have a little negative supply for the bias.

A little further tweakery reduced the 1W THD still further. I think that's about as sweet as I can dial-up. I'm going to build another one and give them a listen.

Thank you, Neslon. I'm encouraged. This sweet spot stuff is pretty fun.

Mike

P.S. Does the low (2X) voltage gain figure seem correct? Also, I believe my samples have the drain connected to the body as the other way around had no gain and worse distortion.
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Old 15th July 2011, 06:46 PM   #5
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That might explain something, although I used them with 2SJ28's in
complementary followers with case = Source and got the following curves:

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Old 15th July 2011, 06:48 PM   #6
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Also, my single-ended result had 3 dB of gain. I might note that I expect
300 light bulbs to come out around 22 ohms. With 2 in parallel, that would
be 11 ohms, so something's off.

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Old 15th July 2011, 07:01 PM   #7
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Breaking news: the 2SK82 was rated at 95 watts (25 deg C case temp).

Another similar Sony part does have the case = Drain. I'll have to check
my results when I get back from the coast.

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Old 15th July 2011, 07:30 PM   #8
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Quote:
Originally Posted by Nelson Pass View Post
Breaking news: the 2SK82 was rated at 95 watts (25 deg C case temp).
Quote:
Originally Posted by Nelson Pass View Post
Also, my single-ended result had 3 dB of gain.
Good news there!

Quote:
Originally Posted by Nelson Pass View Post
I might note that I expect 300 light bulbs to come out around 22 ohms. With 2 in parallel, that would be 11 ohms, so something's off.
I'll check all that and try another device to be sure. I have my gates set at -3V.

Thank you. Have fun at the coast!

Mike
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Old 15th July 2011, 07:42 PM   #9
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I pieced together a 2SK82 curve and compared it to my notebook values
when I tested the parts. It's not a very good match. I'm going to assume
that case=Drain for the time being. Meanwhile, here's that curve which is
good:

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Old 15th July 2011, 07:59 PM   #10
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I read that the 2SK82 has 2 dies and they have to match or one will die!
Did you get them from the Singapore seller on Ebay?
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