3) An extremely low amount of AC noise at its output
          4) A low drop-out voltage
          5) Good overload characteristics
          6) Reliability
          7) Low cost and small size

What Makes Up a Voltage Regulator?
Three features are common to all regulators, whether they are low or high voltage regulators: a voltage reference to calibrate the output voltage, a pass device to adjust the current delivered to the load, and a feedback mechanism to respond to errors at the output of the regulator.

Voltage references can be made from neon bulbs, zener diodes, precision current sources feeding precision resistors, VR tube, or a precision voltage reference IC. In all cases, the voltage derived will serve as a yardstick for the regulator to reference its output voltage. Obviously, the more accurate and stable the voltage reference the better. The reference voltage need not be identical with the output voltage as it can be scaled up or down with feedback and a voltage divider.

The pass device (AKA, losser element) is usually placed in series with the load and it controls the current being fed into the load. It must be able to function over a large variation of current demands--from no load to full load. And it must be capable of withstanding the heat produced in it as the current that passes through it times the voltage across it equals the heat generated. Tubes, both triodes and pentodes, transistors, MOSFETs, FETs--all can be used as pass devices.

A feedback mechanism within the regulator works by sampling the output voltage and comparing it to that of the voltage reference. The difference voltage constitutes an error signal, which is then fed back into the control portion of the circuit to increase or decrease the flow of current through the pass device of the regulator. The control element is another way of saying a negative feedback mechanism, which can be made up of as little as only the pass device's degenerative feedback from cathode-to-grid, or emitter-to-base, or source-to-grid; or a circuit as complex as any power amplifier.

    Review of the three elements of a regulator:
        1) A voltage reference to calibrate the output voltage
        2) A pass device to adjust the current delivered to the load
        3) A feedback mechanism to respond to errors at the output of the regulator

Circuit Design
From the above description of a regulator, it is obvious that an all tube high voltage regulator could be designed and built, but it would prove very complex and probably fail to meet, at very least, our third design goal: extremely low AC noise. Two problem areas for tubes are relatively weak transconductance and susceptibility to microphonics, both of which limit the amount of noise free operation we can expect from a tube. So with all due  apologies to the hard core tube fans, here is an all solid-state design.

It boasts a very low output impedance, a very small idle current overhead, a limited amount of high voltage parts, a very accurate output voltage, a low drop out voltage, a very low noise output, a slow turn-on and a good immunity to blowing up. For critical applications, such as, any circuit that your ears might be subjected to, this the first choice in regulators.

The OP Amp has its own power supply, which is derived from the voltage doubling and rectifying of the 6.3 VAC winding. This where the name "floating" comes from--the IC can draw as much current from its power supply as it needs, without making any demands on the high voltage power supply. This