EL84 driver stage

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catalin gramada

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Joined 2007
#1
Hello. found a bunch of el84 I can use to drive a pair of kt88. I understand can be a very good candidate for that instead a 12au7.Unfortunately I did not found in any datasheet design refereces how to implement it in triode mode.I expect a moderate gain around 20 into 100k load with ca. 3v at input.
Can I conect screen grid to plate and use the graph caracteristics and design like any regular triode?I don.t know how to design the stage. Can You help me with one sugestion.please? Thanks.
 
#3
Thank you. The grid leak should be max 220k as for pentode or can I do it as big as 1M.for instance. Please? I.m not familiar to use EL84 like a regular gain stage so a lot of questions goes through my mind please understand.thanks.
 
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#7
You could try it like this if you're feeling lazy (like I often am). Lovingly drawn in paint 😛
Don't forget to add your grid leak, input cap, etc. I would keep the grid leak at 300K (or lower, if you want) and the tube should last a long time.
 

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#8
Thank you for kind replies. One more question please...Saw in datasheet max g2 voltage to 300v. That means max peak voltage.please? I wonder for what consideration the limited value is 300v? Maybe for triode conection the same demands will not be applied here and can raise the g2 max peak voltage up to 560v.exactly like for plate as time are connected together. I asked cause a supply 450-500v is more convenient for me.with a 10-12k at ca.15mA draw will put the anode arround 300v at idling what should be max acceptable .Thanks
 
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#13
Hi. I did not found any info how much plate current should I draw for el84 in triode mode to keep internal resistance into a optimal 2-3k and how much total distorsoon should I expect from a differential without a ccs compensation in a tail.please? Thanks.
What should be considered a good point to start.please?
 
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#18
You are not designing a power amplifier so the load for the EL84 is the recommended grid resistor of the KT88, which is 100k for fixed bias and 470k for cathode bias. The distortion will be very low because it is very lightly loaded.
 
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