6P45S/EL509 input capacitance in triode mode - diyAudio
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Old 10th February 2013, 12:20 PM   #1
50AE is offline 50AE  Bulgaria
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Default 6P45S/EL509 input capacitance in triode mode

Does anybody have any info, because I finally want to know what driver output impedance I need theoritically to combat the input capacitance of this tube?
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Old 10th February 2013, 07:02 PM   #2
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According to 6P45S datas the input capacitance Cg-k ( BXOДHaЯ) is 55 pF.
Amplification factor in triode mode is only some 2.3 to 2.7.
Therefore the Miller capacitance is very low.
I would assume the total input capacintance is (well) below 100 pF.
As a reference the input capacitance of 12AX7 is essentially bigger, some 160 pF.

Edit: I also looked at the Svetlana EL509 datas and there the Cg-k is only 25 pF.
Therefore I assume that the input capacitance value ( 55 pF) given at 6P45S datas obviously include the Miller capacitance, but at the pentode mode.
Anyhow the input capacitance of triode connected EL509/6P45S seems so low that any special requirements for the driver stage do not exist.

Last edited by artosalo; 10th February 2013 at 07:10 PM.
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