This is not a replacement for the existing PS-21, but is a brother tube power supply (note the B in 'PS-21B"). Just like the PS-21, the new PS-21B holds three independent regulated power supplies: one high-voltage and two low-voltage regulators. (Note the three heatsinks.) Unlike the PS-21, the PS-21B uses a voltage-doubler-rectifier circuit for the low-voltage regulators. Why? Answer: 6.3Vac secondaries.
For two decades now, I have been told by audiophiles whose ears I trust that giving each channel its own separate heater power supply improves the sound, specifically, the stereo imaging. The culprit might be the heater-to-cathode capacitance, which could provide a path for inter-channel mixing of signals. The PS-21 sidesteps this potential problem by giving each channel its own separate heater regulator.
The assumption is that the two low-voltage regulators will be set up to deliver 12V or 12.6V. Many, many audiophiles insist on 6.3Vdc, as they cannot imagine placing to two 6.3V heater elements in series—apparently the universe simply isn't that rich and compliant. But a very good argument can be made for running a 12Vdc output voltage, as it effectively doubles the amount of current the regulator can pass and it gives the regulator more voltage headroom. In general, low-voltage power supplies and regulation is pain with linear regulators, which is why switcher power supplies are so popular and ubiquitous.
The PS-21B could be used with many tube circuits. For example, often we are limited in our designs by the relatively low heater-to-cathode voltage limit (usually 100V), so we cannot use as high a B+ voltage as we might like or design multi-tier efforts, with some tubes situated high above ground potential, while other sits far down at a negative power-supply rail voltage, with far too much voltage between top and bottom cathodes to allow a single heater power supply to be used.
Still another possibility is to make a bipolar, low-voltage power supply out of the two low-voltage regulators. Think tube-hybrid headphone amp, with tubes driving solid-state devices; or hybrid phono stage, with low-noise OpAmp driving a tube circuit.
The another possibility the second low-voltage regulator can power a stand-alone DAC. Some DACs require 12Vdc, others 9Vdc or 5Vdc. A good linear regulated power supply can make a huge improvement in sound over the cheesy switcher wallwart that came with the unit. In other words, we build a tube-based buffer or line amplifier and power the DAC with from the same power supply PCB.
The PS-21B high-voltage series regulator is an all-solid-state regulator designed to deliver between +100V to +300V worth of B+ voltage. The PS-21B regulator maintains a fixed DC voltage and it works to eliminate any AC perturbations on its output. The PS-21 regulator uses an LD1085 as the voltage regulator and an IXCY 10M45S constant-current source to shield the LD1085 from the high-voltage. The LD1085 is nested in its low-voltage span of just a few volts, while the IXCY 10M45S sees the bulk of the input/output voltage differential. Consequently, the IXCY 10M45S gets the heatsink, while the LT1085 is left naked.
The PS-21B PCB also holds two separate low-voltage, 2.5A regulator circuits for the heaters. The low-voltage regulator's rectifier configurations is a full-wave voltage doubler circuit, with no center-tap. Thus, the two 12Vdc outputs can be derived from two 6.3Vac transformer secondaries. Kit comes with resistors for setting two output voltages: 12V, and 12.6V.
Kit does not include a power transformer, but works with transformers between 120Vac to 260Vac (or 200Vct to 550Vct), with 6Vac or 6.3Vac windings. The PS-21B can deliver up to 50mA of high voltage and is the prefect choice for a line stage amplifier or a phono preamp.
The PS-21B regulator kit includes
High-quality PCB that is 4.5 by 6 inches, extra thick (0.93"), with 2oz copper traces, with four mounting holes
All the resistors needed
All the capacitors needed (Nichicon, Panasonic...)
Three LD1085 low-dropout voltage regulators
Three heatsinks for TO220 devices
Four sets of PCB standoffs with O-rings
Four MUR410G ultrafast 4A/100V rectifiers
Four HER108 ultrafast 1A 1000V rectifiers
One IXCP 10M45S HV constant-current source
24-Page User Guide