Tube Power supply
The tube power supply project
This project was an attempt to build a tube amplifier power supply for my 6550 push pull dual mono amps. I already had a really ugly tube power supply in my rack and in early 2000 I decided to design and build from the scratch a new tube PSU.
The importance of using tube rectifiers for the power supply
As we know solid state diode rectifier circuits, are not very effective for tube amps, because they generate fast impulsion that pass through the circuit. Using a full wave tube rectifier circuit for producing direct voltage, we can prevent hum pulsations, and we can achieve more accurate filtering.
Voltage regulation and Filtering
The output voltage of a tube power supply always decreases as more current is drawn. This happens not only because of increased voltage drops in the transformer and filter chokes, but also because the output voltage tends to soar the peak value of the transformer voltage as a result of first capacitor charging. Proper filter design is the key for eliminate the soaring effect.
Voltage regulation is expressed as a percentage between the change in output voltage with load.
Percent regulation = 100*(E1-E2)/E2
where E1= no load voltage value and E2= full load voltage value.
Power supply Filtering
There are two main power supply filter classifications : Choke input filters and capacitor input filters.
Capacitor input filters are useful with solid state diode rectifiers.
Choke input filters permits better utilization of tube rectifiers, because higher load current can be drawn without exceeding the peak current rating so we can achieve better voltage regulation results.
A choke input filter usually act as a capacitor filter unless the input choke has at least a certain minimum value of inductance called critical value. For full wave 60Hz tube supplies this value is given by
L(Henrys) = E (volts) / I (mA)
E=supply output voltage
I=the current drawn through the filter
this is the tube power supply schematic: