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Old 4th November 2007, 09:32 PM   #1
nesha is offline nesha  Serbia
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Default parallel EL84 transconductance amp

Hi. I m reeealy interesting in making my first el84 tube amp in SE parallel configuration, and I would like to modify schematics of transciductance amp I have found on MagneQuest forum.OK , I know it is infected with SS devices ( those mosfets are in signal way) but the fact that amp would make fullrange driver go deeper in bass region is irresistible to me.So, can I just add 2 el84 more, and use 1/3 inn impedance OPT , or diferent biasing of mosfets is needed? Or how about diveloping Decware Zen with 3 el84? Maybe diferent input/driver tube is needed for extra current? And what tradeoffs should I expect with paralleling output tubes? Fullranger I had in mind is Audio Nirvana super 12 (incredible flat impedance , rising inbass region would work sinergesticaly with transcoductance amp, God bless N. Pass..., and high sensitivity... yammie). Help! Thanks
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Old 5th November 2007, 09:35 AM   #2
Jaime is offline Jaime  Uruguay
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You know the 9watts EL509 tube transconductance amp at the Magnequest forum?
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Old 5th November 2007, 12:17 PM   #3
Klimon is offline Klimon  Belgium
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Here's a tested schematic for el84 parallel SE: http://www.diyparadiso.com/piccolo4.htm

tip: WE407a (20/40v heater) makes a cheap replacement for 2c51.

Driver requirements are the same for parallel and single el84 (atleast voltage swing, input capacitance doubles but 'll hardly be problematic with el84). When redesigning a single el84 for parallel output you'll also have to adjust cathode resistor and bypass to maintain same operating point (use ohms law). For the opts I'ld aim for 2-5K Zout.

Simon
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Old 5th November 2007, 10:38 PM   #4
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Can somebody comment on why the amp in the original post is a *transconductance* amp? The output side looks like a traditional parafeed, so what's the big deal?
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Old 5th November 2007, 10:52 PM   #5
Jaime is offline Jaime  Uruguay
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You have information here >>>
http://db.audioasylum.com/cgi/m.mpl?...e+amp&session=

Best regards Jaime
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Old 6th November 2007, 12:12 AM   #6
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Quote:
Originally posted by Jaime
You have information here >>>
http://db.audioasylum.com/cgi/m.mpl?...e+amp&session=
That link just gives a definition for "transconductance amp", which I already knew. Maybe I should have just said "What's the big deal about that circuit?"
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Old 11th November 2007, 08:51 AM   #7
nesha is offline nesha  Serbia
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Thanks guys, I ll try to actually do something now, I still cannot decide should I go for high power KT88 (or parallel el84) or "more purity" single el84 design."Maby" it is time to stop endlless reserch.
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