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grid drive and diode sound

81.31.233.143

Posted by Nikko on March 13, 2007 at 04:42:25

Hi. I am driving a pair of 5881 in class AB2, with positive grid drive. When pushing this amp as hard as possible, actually letting it clip at some passages, I get this nasty sound now and then. It sounds like the speaker voice coil is loose and scratching against something, only very loud and pretty unfriendly harmonics wise.
Is this the sound of the tubes going into grid-cathode diode conduction, or whatever it is called?
Am I driving it with too high impedance? I use a 1:1+1 interstage and a 6922 runnning at 6mA as a driver. The gridresistors are high, 100kohms, because I want the interstage tranny to dominate. Lower resistances flattens the freq respons, but I prefer the sound of higher resistance.

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