Hi All, For those of you who ABSOLUTELY abhor solid state solutions, yet would like to run your preamp tubes from a regulated DC supply... I present, in a somewhat whimsical fashion...... (ta da)...... Using the 2050 Thyratron as a shunt regulator (zener) to provide a regulated 12 volt to your preamp tubes. Background: The 2050 will tolerate a maximum of 100 mA cathode current, and being a gas tube, has low drop when it is conducting. In fact, being a tetrode, the G2 (shield) causes a somewhat negative resistance effect of current vs voltage. This means that by putting a series (positive) resistor in the circuit, there is aome point where the net resistance is zero, and "perfect" regulation occurs. For the 2050, the effective "zener" voltage at this zero resistance point is about 11.5 volts, so that it can power your preamp tubes. To achieve this about 22 ohms is added in series with the 2050 The zener action is very similar to all zeners.... As an example, let's assume you want to regulate 2 12AX7 tubes. This would require the supply provide 12 volts at about 300 mA. If we draw an average current in the 2050 of 50 mA, the regulation is valid for currents of 300 to 300 mA (causing the 2050 current to vary from 0 to 100 mA.) Topology: Now. What is the circuit like. Lets start with a 24V transformer, and bridge rectify and filter it. The output voltage will be about 32.0 volts. For an average current of 350 mA and a voltage drop of (32-11.5) 20.5 volts, the series dropping resistor is 58 ohms. Lets use a 56 ohm 10 watt resistor. Circuit (use a fixed font to view this)... Rectified DC = 32 volts----[56 ohms]------+----- to 12AX7's | | adjust regulation by adjusting ---> 22 ohm 5W | +---\ | | 2050 --- | - - --/ /--- - - 2050 pins: | _____ heater: 2,7 | | | plate: 3 | | /\ G2: 6 | | || G1: 5 | | 6.3V, .6A cathode: 8 gnd gnd Regulation characteristics: 2050 current Regulated Voltage 5 mA 10.95 V 10 11.66 20 12.10 40 11.71 60 11.34 80 11.36 100 11.40 110 11.60 This circuit will "regulate" over the range of the Filtered DC voltage of 28.5 volts to over 34 volts, and with 32 volts applied, will convert 4 volts of "ripple" to about 300 millivolts. (with lower input ripple, the output ripple is correspondingly lower; notice that over the range of 50 to 100 mA, only 26 mV change occurs). Enjoy, Steve