Hi guys

I was looking into a tube circuit the other day, they usually operates between 100 - 150 VDC, one thing I am curious about, why they don't use a high voltage regulator in vacuum tube amp?? Instead, they use some simple RC filter to filter the DC voltage.

 

Had to look it up.

There are voltage regulator tubes. So, maybe, one of the tubes in your circuit is such voltage regulator.
http://en.wikipedia.org/wiki/Voltage-regulator_tube

 

because the voltage supply isnt as critical in tube amps. a solid state amp with a 12 volt supply is a lot more critical for supply voltage because they start with so little and are current operated. the tupe amp starts with much higher voltage, so the actual voltage isnt as critical. some circuits such as oscilators and dc amps require regulation, but not most circuits.

 

For most receiver and power tube circuits the actual plate voltage was not critical and when it was required (in things like radar repeaters) most tube regulator circuits used shunt type regulators so they wasted power. I still have a few triode tube shunt regulator modules for high voltage bias supplies at work.
http://www.tubecad.com/july99/page12.html

 

Tubes are relatively expensive so they don't use a tube for regulation unless it's really required by the circuit.