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-   -   Diode trick? (http://www.diyaudio.com/forums/tubes-valves/76960-diode-trick.html)

Giaime 2nd April 2006 01:20 PM

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. :)

SY 2nd April 2006 01:49 PM

You are not wrong, there are some mistakes in there. Also some bald assertions and unsupported claims.

poobah 2nd April 2006 03:35 PM

Bald people making assertions always makes me nervous... got hair?

kathodyne 2nd April 2006 06:38 PM

i've also discovered these articles, and asked questions about it....conclusion....it's BS.

Giaime 2nd April 2006 06:40 PM

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? :xeye:

SY 2nd April 2006 06:43 PM

No, Bill's idea isn't nutty. I've also seen something similar done with a floating DC supply- was it Audio Research?

Giaime 2nd April 2006 06:57 PM

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 :D with maybe 15k load...), 807, KT88...

Dave Cigna 2nd April 2006 10:11 PM

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.

rdf 2nd April 2006 10:59 PM

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."

plovati 2nd April 2006 11:24 PM

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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