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Tube voltage limits and tube regulators

1/26/2006 9:15 AM
Hiatt Collins
Tube voltage limits and tube regulators
I've been looking at tube regulators, specifically a series-pass design.  
Say I wanted to use a tube regulator to drop a B+ of 475V down to 250V for a screen supply, and wanted to use a tube like a 6AQ5 or EL84 to do it. I've got the plate and screen tied together and sitting at 475V, and the cathode and heater both sitting at around 250V.  
I've only got 225V across the tube, which would be well within either tube's rating if I had the cathode and filament at 0V and the plate/screen at 225V.  
I'm guessing that it's the voltage across the tube that matters (like in a cathode-bias arrangement), not the absolute voltage. Is this the case? Does the tube 'know' that it's sitting at a voltage higher than its ratings, even though the voltage across it is well within them?  

Ray Ivers Hiatt,Since you're ... -- 1/26/2006 9:44 AM
MBSetzer Check this out, it is an adjustable... -- 1/26/2006 11:01 AM