12AX7 plate voltage exceeds rated max
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12AX7 plate voltage exceeds rated max
What's the consensus on running 12AX7 plates over their max rated voltage of 330VDC. I've noticed certain phase inverter tubes are running upwards of 350V on the 12AX7 plates. The Hiwatt DR504OL schematic shows 356V/347V on each side of the PI plates. Are more rugged tubes recommended, or are their limits capable of being pushed a bit? I know certain reverb and tremolo tubes run at higher voltages, but I figure the difference in application is relevant.
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JazzGuitarGimp
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Re: 12AX7 plate voltage exceeds rated max
Max plate voltage is specified with respect to the cathode. Notice on your schematic, that the cathode voltage on the PI is 78V? Subtract 78 from the plate voltage to see how much voltage is actually across the tube.
Last edited by JazzGuitarGimp on Thu Dec 03, 2015 3:17 am, edited 1 time in total.
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gingertube
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Re: 12AX7 plate voltage exceeds rated max
Also note that a 12AX7 has a zero current voltage rating of 550V. So no need to worry about startup with cold heaters and zero current.
Cheers,
Ian
Cheers,
Ian
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Smokebreak
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Re: 12AX7 plate voltage exceeds rated max
SSS runs a post PI ax7 driver with high voltage. Those seem to survive.