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Old 7th April 2006, 04:20 PM   #1
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Default Ok to exceed Vg2 in triode? (Yes)

That was my question until doing some searching and finding these conclusions. This is based mostly on the 6AV5 triode strapped to behave like a 2A3. The datasheet for the 6AV5 says the max Vg2 voltage is 175. However its known that Sylvania sold triode strapped 6AV5s during the 1980s as drop in replacements for the 6B4G. This article on Audioasylum tells some operating points and tips for triode mode.

http://www.audioasylum.com/forums/tu...ges/83032.html

While looking over some datasheets I came across the 6AU5, a somewhat similar and smaller 6AV5. The datasheet lists the maximum Vg2 as 200. On the next page it has specs for use as a voltage regulator with g2 tied to the plate. The maximum voltage listed is 300.

http://www.pmillett.com/tubedata/HB-...01/6AU5-GT.PDF

So at least with these two tubes running them triode strapped won't hurt the screen grid.
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Old 7th April 2006, 05:00 PM   #2
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Quote:
Ok to exceed Vg2 in triode? (Yes)
Maybe.
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Old 7th April 2006, 06:09 PM   #3
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Depends. But most tubes can take more G2 voltage in triode or UL, or (in a guitar amp at least...) with a big enough screen resistor.

Fritz Langford Smith (who is rumored to know something about the subject) used the 807 over its screen voltage rating in his version of the Williamson amp. http://www.retrovox.com.au/A515.pdf
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Old 7th April 2006, 10:21 PM   #4
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Maybe. Yes. Mostly.

Carefully watch averaged g2 power dissipation, though.

Exceeding g2 voltage ratings alone is much less prone to catastrophic failures (eventually resulting in internal g2 arc-over) than exceeding g2 power ratings (most certainly resulting in current run-away, g2 secondary emmissions, eventually g2 meltdown).

Tom
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Old 8th April 2006, 01:56 AM   #5
Nafty is offline Nafty  Israel
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Default G2

Hello every One.
This my second post.
My name is Naphtali and I'm located in Spain.
I've been testing grid and screen grid driven in paralel.
After all, I'm buffering the grid signal in to the screen grid.
I like the resolts and it is an very intersting method.
Did any one tested this type of configuration before?
Do any one have some links where to learn more about this subject?
Regards.
Nafty
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Old 8th April 2006, 02:30 AM   #6
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Could you make a sketch of what you're doing? If it's screen grid drive from a buffer, there are several of us on the forum who have been working with that.
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Old 8th April 2006, 01:47 PM   #7
Nafty is offline Nafty  Israel
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Default G2

Hello every one
Yes, Shy, Iíve been alter this affair of driving pentodes triode connected since long.
The Idea was not waste the power that the pentode may offer.
So, de first idea was try enhanced type of configuration.
Well, it did work for while but power supply was complicated, and I had not the proper transformer to do it so. So one day looking for recommendation, did step on Morgan Lundberg page (http://www.eng.umu.se/personal/morgan/Valvular%20Pages/) and I saw dawn in the corner one interesting idea like drive G1 and G2 in parallel, buffering the signal to G2.
I proved some thing similar and it did work In fact I was impressed by the sound.
Harmonic String was exactly the ones that we may see with single ended configurations. Sound was full of space and air. Here I have to say that I had to be very carefully with the bias of G2 because circuit tends into oscillations. SO far so good, but I had not enough. Today, Iím using spare windings of 16 Ohms from de secondary to drive G2 in phase or 180ļ out of phase. Methods are depending from the tube and the sound that we may to achieve.
Again, did any one try it?
I do think that great triodes are just behind normal penthodes.
Best regards to all of you.
Nafty
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Old 8th April 2006, 08:33 PM   #8
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Default Re: G2

Quote:
Originally posted by Nafty
After all, I'm buffering the grid signal in to the screen grid.
I like the resolts and it is an very intersting method.
Did any one tested this type of configuration before?
Do any one have some links where to learn more about this subject?
Regards.
Nafty
Yes
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Old 8th April 2006, 09:14 PM   #9
Nafty is offline Nafty  Israel
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Default G2

Helo Miles, nice to meet you.
So.. what did you get??
I'm building a new amp based in that principle.
Also, I'm using only "R" core transformers; I mean output and power supply. The "R" Core transformers is one other interesting matter to investigate.
Rgs.
Nafty
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