While not a tube circuit, this month's circuit of the month, a high voltage regulator, makes many tube circuits possible. An MC phono preamplifier requires the cleanest power supply voltage to keep its output noise to a minimum. And this regulator delivers a clean output voltage. It use a floating power supply to power its control circuitry and allow for the use of low voltage parts.

What is a voltage regulator?
Simply put, a voltage regulator is a device that maintains a constant output voltage in spite of variations in either the power supply voltage or the current drawn by the load. A voltage regulator does with complex circuitry what a car battery does by brute force: it maintains a steady and accurate output voltage over a large range of load current. Of course, this analogy suffers from the disparity between the 13.6 VDC the battery yields versus the 400 VDC available from a high voltage  regulator. Thus, a quick adjustment--simply wire 30 car batteries in series to match the output voltage of the regulator. Now we have a fair comparison. Both offer an extremely low output resistance; both display wonderful voltage stability; both are immune to voltage variations resulting from wildly different current loads. Surprisingly, the regulator might beat the 30 car batteries by having a lower output resistance and even greater voltage stability. An amazing achievement when the size of the  regulator, which could fit in a 40 cubic inch box, is compared to the closet needed to house 30 car batteries. However, the battery would surely win in the contest of peak amps of output current.

Design Goals
What attributes does a good regulator embody? Ideally, a regulator should boast an output impedance of zero from DC to light, 100% efficiency (zero power dissipation), immunity to noise and drift of the line voltage, small size, low cost and the capability of withstanding a dime thrown across its output. Well,