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Author Topic: Triode vs. pentode preamps  (Read 16081 times)

maxdimario

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Triode vs. pentode preamps
« on: January 15, 2005, 01:04:10 pm »

Mr. Archut.

You raised a curiosity of mine concerning the triode vs. pentode as an ideal amplifier.

The pentode wired as pentode is usually used in high-gain first stages etc.

I have seen that in the V41 and other amps some of  the ef12 pentodes were wired as triodes.  In the U47 the VF14 is wired as a triode.

Was the choice of using pentodes throughout based on the fact that the pentodes of the time were better built than triodes, or is a pentode wired as triode superior to a standard triode under all respects?

There are some great german SQ gold-pin triodes that have no comparison to the small receiving tubes such as 12ax7 etc. and I was under the impression that when high-gain was not an issue they would work better as they are lower in distortion usually, although they have a different sonic footprint.



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Oliver Archut

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Re: Triode vs. pentode preamps
« Reply #1 on: January 18, 2005, 12:37:00 am »

Hello Maxdimitrio,

first of all nobody calls me Mr. Archut, just Oliver is fine..

You point out a very interesting issues triode vs. pentode in triode connection.

The V41 as well as other V and U series pre amps, the triode connection is due to the tube limitation, only EF12 and 14 were issued by the "Reichs Rundfunk" so in order get rid of gain for an additional buffer stage, they choose the triode connection. The later V76 works in the same place with a very high negative feedback... and an even more special tube than the EF804S the E83F.

There are several times in tube history that a mesh or grid anode surfaced, first in the 1920 to get a better tube performance.
This is a kind of related and Barhausens Handbook of the Vaccumtube suggest a frequency depended character of a grid or mesh triode.
In HF application there is a use for that type of tube, to reduce internal capacitance, but in audio it is hard to quantify.

I did several test of in production mesh anode triodes vs. american and german made NI or P2 solid anode triodes, each time the solid ones worked better, maybe because they were made better.
For some people it is a matter of believe, but here are some ways for you to test and measure.

Did you ever only used the 2nd grid of the pentode as anode? (plate and 2nd grid to ground)
Also did you ever hooked up a beam power tetrode or pentode, were the 3rd grid or beam former are hooked up to the cathode inside the envelop? You might want to try that.

As pointed out that germany is the land of special purpose tubes, some of them have gold plated pins, but most of them were deigned for HF use.

Best regards,


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Oliver Archut
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Radd 47

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Re: Triode vs. pentode preamps
« Reply #2 on: January 18, 2005, 09:29:41 pm »

Ollie, what do you think of the Amperex 6689 as a sub for the harder to find E83F?

Also, what is the circuit board material used in those old 76's? Funny to see them use boards way back then when everyone else was point to point.

Thanks!
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Oliver Archut

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Re: Triode vs. pentode preamps
« Reply #3 on: January 19, 2005, 12:01:07 am »

Hello Radd 47,

the Amperex 6689 is in most cases a Philips made (look for the edged code on the tube) E83F, or later they used the less quality Tungsram made E83F, anyway E83F are still around and easy to get, if you need hints let me know, there are some online tube dealers in germany that carry them for a few bucks..

The EF80 is very similar and sometimes they show up on e-bay for a Dollar each or so... It works just by changing the footprint, noise get a bit higher and the feedback needs to be adjusted.

The circuit board original used was phenolic based, however since 1998 it is outlawed in germany due to the toxic fumes that are generated while burning...
Mostly used in motor and generator application in europe from 1930 to 1980....

In case you need a new circuit board for a burned V76 I have the material in stock for restorations...

Best regards,
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Oliver Archut
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maxdimario

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Re: Triode vs. pentode preamps
« Reply #4 on: January 19, 2005, 06:46:44 am »

Oliver Archut wrote on Tue, 18 January 2005 06:37

Hello Maxdimitrio,

first of all nobody calls me Mr. Archut, just Oliver is fine..



Did you ever only used the 2nd grid of the pentode as anode? (plate and 2nd grid to ground)
Also did you ever hooked up a beam power tetrode or pentode, were the 3rd grid or beam former are hooked up to the cathode inside the envelop? You might want to try that.

As pointed out that germany is the land of special purpose tubes, some of them have gold plated pins, but most of them were deigned for HF use.






thanks for your reply,

I don't get what you mean by hooking up 2nd grid and anode to ground.

you're saying to hook up the screen grid and anode to ground??

and the 3rd grid or beam former to cathode?   like el86 or 6l6gc?
valvo  e83f is a mesh-anode pentode... RF tube?

I am afraid I don't get the point, but my question was concerned with your personal opinion regarding triodes in preamps.


anyway, the gold-pin tubes I was referring to were e88cc and the like.
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Oliver Archut

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Re: Triode vs. pentode preamps
« Reply #5 on: January 19, 2005, 11:07:24 am »

Sorry for the typo, it should read 2nd grid as anode, 3rd grid/ beam former and plate to ground, so you run the pentode as a mesh/grid plate.
Also if you hook up a tube like the EF732/5840in a preamp as a triode, or the EL84 in a power amp as triode, the 3rd grid is connector to the cathode inside the tube... It sounds quite different, hooking either the plate to ground or connect it with the 2nd grid as anode...

In my personal opinion a pentode has a fuller and warmer sound, triodes are good as a buffer amp with nearly no gain, unless you go into the world of non linear amplifiers like Fender an alike....

The ECC88 family of tubes was the last great tube development that spun developmenents like the EF97 neutrode. The ECC88 was a design in first order for UHF and VHF tuners and antenna amplifier. Even it is a HF tube it found its way into audio  and is also direct responsible for the later ECC803s design. Seeing it from a design standpoint those frame grid designs are great tubes, but listing to them is a different world.

best regards,



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Oliver Archut
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We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

maxdimario

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Re: Triode vs. pentode preamps
« Reply #6 on: January 21, 2005, 12:09:06 am »

Oliver Archut wrote on Wed, 19 January 2005 17:07


In my personal opinion a pentode has a fuller and warmer sound, triodes are good as a buffer amp with nearly no gain, unless you go into the world of non linear amplifiers like Fender an alike....

best regards,







Oliver,

Thanks for sharing your opinion, I have to agree about the fullness and warmth of pentodes.
My favourite german special quality triode was designed for analog computers.....love that tube! almost as much as the ef804 and the ef12 for audio!
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