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Old 7th November 2005, 01:22 AM   #1
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Default EL34 Triode Mode - G3 where?

When running EL34s in Triode Mode is there any advantage in wiring G3 to the anode (via say 1K) rather than connecting it to the cathode or to a small negative voltage?
Anyone noted any sonic benefit or measured any worthwhile difference?
Thanks,
Ian
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Old 7th November 2005, 06:47 AM   #2
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Default pseudo-triode

Hi (to all)... !

When wiring pentodes in triode mode, the rule of thumb is to connect g2 to a, preferably thru 200 ohms - 1k ohms resistor (grid stopper to prevent oscillation).

Most pentodes to not have a separate pin connection for g3 -- one of the very few that comes to mind is the EL34.

In order to have a true pseudo triode, you should connect g3 to anode, as well. If you do not, it will still work as pseudo triode, but you would loose the possibility to make it as triodelike as possible.

It's up to you and your taste, bat-eared people might hear some difference, or make themselves believe that they do hear it. Anyway, it will work and quality as pseudo-triode both ways. Just do not forget the grid stoppers!

Further on this topic, I recall having seen some true triode EL34s being manufactured without the g2 and g3 material, in order not to interfere with the flow of electrons. Because, you know -- the electrons will not reach the anode and the g2 and g3 material at the same time, actually.

Best regards,
Aleksandar

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If you need the sound of the triode with the power of the pentode, try the RH34! ) (this was a little self-advertising)
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Old 8th November 2005, 02:24 AM   #3
G33/33 is offline G33/33  Indonesia
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Default Re: pseudo-triode

Quote:
Originally posted by Alex Kitic

In order to have a true pseudo triode, you should connect g3 to anode, as well. If you do not, it will still work as pseudo triode, but you would loose the possibility to make it as triodelike as possible.


If you need the sound of the triode with the power of the pentode, try the RH34! ) (this was a little self-advertising) [/B]

Hi Mr. Kitic,

I find RH34 in Elvis Rakic website, but no rfb value there.
Should it be 100K ?

and if i want to make a true pseudo triode, may I just disconnect g3 from cathode and connect it to anode via 200 Ohm resistor ?


rgds,
Gede
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Old 8th November 2005, 11:00 PM   #4
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I have connected g3 directly to the anode w/ el34s and found it preferrable. ymmv.
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Old 9th November 2005, 07:19 AM   #5
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Default RH34 and pseudo-triode

Hi to all!

First of all, whoever might be interested in the RH34 schematics should contact me directly via e-mail. You can find my e-mail address both on Elvis's and my site www.tubeaudio.8m.com

Last but not least, all RH amps can have a switch to allow transforming them from RH to pseudo-triode, even in real time (although that is not recommanded, you should first turn it off than apply the switch position...). But, the real reason for the switch to exist is to give disbelievers the opportunity to hear for themselves that the sound is the same (almost, especially for those bat eared) while the power is vastly different... and those who own extremely efficient speakers and necessitate no more power than that of a 10Y or eventually 45... well, they most probably do not need an RH amp, they need to assess their own wishes and not let themselves be commanded what to do by would-be-designers of true triode amps

Regards,
Aleksandar
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Old 9th November 2005, 08:16 AM   #6
EC8010 is offline EC8010  United Kingdom
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Default Re: pseudo-triode

Quote:
Originally posted by Alex Kitic
Because, you know -- the electrons will not reach the anode and the g2 and g3 material at the same time, actually.
Electron transit time becomes important at microwave frequencies but is entirely negligible at audio and even low RF. Assuming 400V on the anode, the electrons will strike it at almost 12,000,000m/s* Eyeballing an EL34, the furthest point on the anode from the central cathode structure is about 8mm, so assuming uniform acceleration, an electron will take 1.3ns to traverse that entire distance.

I really don't think even large discrepancies in a total transit time that amounts to less than one hundredth of a degree of phase at 20kHz are going to be a problem...

Oh, and to get back to the original poster's question, connecting g3 to a pentode's anode when in triode mode gives a small (but measurable) increase in mutual conductance. I've no idea if it's audible, but if it's free and it doesn't cause oscillation, why not have it?


*About 26 million miles per hour
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Old 9th November 2005, 10:12 AM   #7
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Hello,

I have recently conducted some tests with G3 connected to the anode.

Here is the distortion spectrum of an EL34 at full undistorted power with G3 connected to the cathode (the normal way):
Click the image to open in full size.

And here is the same circuit with G3 connected to the anode:
Click the image to open in full size.

As you can see the measured distortion figure is about equal but the harmonic distribution is very different indeed.

Best regards
Michael
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Old 9th November 2005, 10:19 AM   #8
EC8010 is offline EC8010  United Kingdom
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Now, that is interesting. I had wondered whether the g3 connection might make a change to the distortion spectrum. Clearly, it's worth using EL34 with the traditional connection. Which make of EL34 was it?
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Old 9th November 2005, 11:36 AM   #9
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Hello,

Quote:
Originally posted by EC8010
Which make of EL34 was it?
it was an East German RFT.

Best regards
Michael
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Old 9th November 2005, 07:46 PM   #10
rdf is offline rdf  Canada
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Hi tubemaster,

Were G2 and G3 directly connected to anode or via resistors? Also curious if you looked at frequecy response. This is conditional because I didn't write down the measurements, but I seem to recall playing with an E180F that tying G3 to cathode resulted in a wider bandwidth up top compare to anode connect.
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