Matador...here's another suggestion on the power supply...
Find a small power transformer with 120 volt (40 ma) and 12 volt (0.6 A) secondaries. Bridge rectify both secondaries. For the HT, come off the bridge rectifier through a 8 k resistor to the anode of a 0A2 voltage regulator tube (cathode of the 0A2 to ground). Then use two or 3 R/C networks to get the HT down to 120 volts. The 0A2 will force the supply voltage at the anode to 150 volts so you don't have a surge while the mic tube (6072) heats. The current drain off the HT supply is minimal. Don't exceed the 60 volt capsule voltage...I assume the capsule voltage is derived from a resistive divider off HT to ground..
The heater voltage should be adjustable, using an adjustable resistor. If you use L/C sections, put it before the first choke. If you use a solid state current pass, put it after the pass transistor. The IR drop across the choke(s) may put you in the correct voltage range. Last but not least, you may want to hang a zener diode across the heater DC somewhere in the circuit to crowbar the voltage if something fails.
Use single point ground for the wiring. This should stop any nasty ground loops from multiple grounded components in the PSU when working at mic level.
A 6072 is a low noise 12AY7...pins 4 and 5 are the heater, and pin 9 is the heater center tap. You may find that running the 6072 heater at 12 volts (dc) keeps the IR drop in the PSU to mic cable at a minimum, as well as coupled noise. (The 12 volt connection is across pins 4 and 5 of the 6072 with no connection at pin 9.)
Be careful when working on these supplies since the HT filter caps hold a charge for a good while even if the unit is turned off.
Find a small power transformer with 120 volt (40 ma) and 12 volt (0.6 A) secondaries. Bridge rectify both secondaries. For the HT, come off the bridge rectifier through a 8 k resistor to the anode of a 0A2 voltage regulator tube (cathode of the 0A2 to ground). Then use two or 3 R/C networks to get the HT down to 120 volts. The 0A2 will force the supply voltage at the anode to 150 volts so you don't have a surge while the mic tube (6072) heats. The current drain off the HT supply is minimal. Don't exceed the 60 volt capsule voltage...I assume the capsule voltage is derived from a resistive divider off HT to ground..
The heater voltage should be adjustable, using an adjustable resistor. If you use L/C sections, put it before the first choke. If you use a solid state current pass, put it after the pass transistor. The IR drop across the choke(s) may put you in the correct voltage range. Last but not least, you may want to hang a zener diode across the heater DC somewhere in the circuit to crowbar the voltage if something fails.
Use single point ground for the wiring. This should stop any nasty ground loops from multiple grounded components in the PSU when working at mic level.
A 6072 is a low noise 12AY7...pins 4 and 5 are the heater, and pin 9 is the heater center tap. You may find that running the 6072 heater at 12 volts (dc) keeps the IR drop in the PSU to mic cable at a minimum, as well as coupled noise. (The 12 volt connection is across pins 4 and 5 of the 6072 with no connection at pin 9.)
Be careful when working on these supplies since the HT filter caps hold a charge for a good while even if the unit is turned off.
