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Old 2nd April 2006, 01:20 PM   #1
Giaime is offline Giaime  Italy
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Default Diode trick?

http://www.t-linespeakers.org/tubes/triode-trick.html

I understand the article, but...

What about this?
http://www.webace.com.au/~electron/tubes/oes.html
http://www.webace.com.au/~electron/tubes/triode.htm

I don't quite understand what this guy says. If I'm not wrong, there are a few errors in there.

Could someone explain me what's behind putting a single forward biased diode in series with the screen? I understand the first article (where a Zener string, AC bypassed, is used), but can't comment on the others.

Thank you in advance, and excuse me if it has already been topic of discussion.
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Old 2nd April 2006, 01:49 PM   #2
SY is offline SY  United States
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You are not wrong, there are some mistakes in there. Also some bald assertions and unsupported claims.
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Old 2nd April 2006, 03:35 PM   #3
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Bald people making assertions always makes me nervous... got hair?
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Old 2nd April 2006, 06:38 PM   #4
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i've also discovered these articles, and asked questions about it....conclusion....it's BS.
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Old 2nd April 2006, 06:40 PM   #5
Giaime is offline Giaime  Italy
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Thank you all!

But this idea
http://www.t-linespeakers.org/tubes/triode-trick.html
doesn't seem so bad to me. I will try it.

I'm also thinking that if we can establish a fixed potential difference between anode and G2, we can up plate voltage (gaining power) mantaining G2 in its ratings.

Or not?
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Old 2nd April 2006, 06:43 PM   #6
SY is offline SY  United States
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No, Bill's idea isn't nutty. I've also seen something similar done with a floating DC supply- was it Audio Research?
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Old 2nd April 2006, 06:57 PM   #7
Giaime is offline Giaime  Italy
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Some examples:

6V6: max G2 = 315V, max A = 350V, one could increase plate voltage w.r.t G2 voltage by a good 10%.

Also old 6L6 (not GC), maybe even EL34 (what about trioded with 700V on the anodes with maybe 15k load...), 807, KT88...
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Old 2nd April 2006, 10:11 PM   #8
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Quote:
Originally posted by SY
No, Bill's idea isn't nutty. I've also seen something similar done with a floating DC supply- was it Audio Research?

I'm not familiar with that, but a few years ago there was an article published in an electronics magazine (not audio based) where the author suggested using a floating supply to raise the screen voltage above that of the plate. The claimed result was that the lower plate voltage meant that more current could be run without exceeding the plate dissipation limit. I don't think the author considered screen dissipation, nor did he consider that a simple zener could provide the same level shifting without the capacitive load of a floating supply.
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Old 2nd April 2006, 10:59 PM   #9
rdf is offline rdf  Canada
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Hi Giaime, doesn't Bill Pearl provide an explantion for the forward biased screen diode?


Quote:
"The 1N914 prevents the screen's going into a runaway "negative impedance" mode where is it emitting, rather than collecting, electrons."
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Old 2nd April 2006, 11:24 PM   #10
plovati is offline plovati  Italy
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Default EDN design idea

Yea,
was a boosted triode presented as one EDN Design Idea
by Dave Cuthbert

Here's the link:
http://www.edn.com/contents/images/61203di.pdf

Good to squeeze out all the milliWatts from a chep tube, at a price of power supply complication. The increase expense maybe used to buy a better tube with better and safer results.
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