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Old 18th October 2004, 09:00 PM   #1
percy is offline percy  United States
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Default EL34 best for triode strapping ?

I noticed that the internal structure of the EL34 is different from all other popular pentodes that are out there currently in the sense that the suppressor grid is not tied to the cathode internally, but all others that I checked had the cathode tied to the grid internally.
Does this give EL34 any advantage in being used as a triode strapped pentode over other pentodes ?
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Old 18th October 2004, 09:45 PM   #2
alejo is offline alejo  Argentina
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in other simil post "SY", one moderator in this forun it put east link,


http://www.decware.com/paper16.htm
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Old 18th October 2004, 10:25 PM   #3
percy is offline percy  United States
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I am familiar with the link and SY's reply also, and that article touches this subject, however, I wanted to check as to what others thought about that fact (EL34 architecture and its implications in triode strapped mode).
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Old 19th October 2004, 12:45 AM   #4
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Default EL34 as a Triode

Menno van der Veen in "Modern High End Valve Amplifiers" claimed that the Ia vs Va curves shifted to the left. That is more Anode Current for the same Anode Voltage when using a true Pentode in Triode Mode compared to using Beam Power Tetrode in Triode Mode.

This would have the benefit of requiring a lower power supply voltage.

It was interesting to note however, that in his subjective assessment of the actual amplifier in question he preferred KT66 (a beam power tetrode) in Triode Mode to EL34 (Pentode) or 6550 (Beam Power Tetrode)..
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Old 21st October 2004, 08:49 AM   #5
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Steve Bench's web site has a schematic of an EL34 triode-strapped PP amplifier in which he connects the suppressor grid to the plate (via a stopper) instead of to the cathode. He doesn't say much about it but I understand that some people prefer the sound of that configuration. I haven't tried it myself.

Another article I've read (but can't remember where) claims that the EL34 sounds better in triode-mode with the suppressor connected to a -5v supply. Again, I haven't tried this myself.
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Old 3rd April 2005, 08:03 AM   #6
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Quote:
Originally posted by ray_moth
Another article I've read (but can't remember where) claims that the EL34 sounds better in triode-mode with the suppressor connected to a -5v supply. Again, I haven't tried this myself.
That jives with what Bill Perkins has suggested to me... connecting the suppressor via a 3.5V battery to ground...

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Old 3rd April 2005, 07:24 PM   #7
percy is offline percy  United States
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Wow this thread came out of the dead.

But your timing couldnt be better as I was just comparing the triode curves for the KT88, 6550 and EL34 to see which would be the most linear, at what bias and what power.

Wonder which would be the most suitable for triode mode ?
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Old 4th April 2005, 08:05 AM   #8
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For triode connection, the KT88, 6550 and EL34 all have their supporters - and I suspect they're all correct, too! Selection is mainly a matter of how much power you need, how much you want to spend and whether you already have an output transformer that restricts your choice of OP tubes.

It has been suggested that pentodes are inherently more stable than beam tetrodes, regarding their tendency to oscillate. However, with judicious use of grid stoppers and attention to layoyut to avoid long leads, using KT88 or 6550 shouldn't be a problem.
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