Transformer amperage question

[bschifke]

Hello Everybody!

Question about power transformers and voltage doubling circuits etc.

In reviewing the Fender Hot Rod Deville schematic, I am not sure how it has enough current to supply the tubes.
The power transformer has about has 342V between the high voltage lines at 500 mA (as per hammond 290VX replacement transformer spec sheet). The Schematic shows these lines going through what appears to be a voltage doubling circuit to achieve the required plate voltages, BUT this should half the available current to about 250 mA if I understand these circuits correctly.

How then, does the remaining ~250mA of available current provide enough current for 2 x 6L6 tubes and 3 12ax7 tubes? Shouldn't these require closer to 300 mA?

[martin manning]

The HRD schematic HV supply shows a full-wave bridge, so you only have to derate the Available DC current to 62% of the AC (per Hammond's instructions).

[wpaulvogel]

I wish people would stop calling full wave bridge rectifiers a doubling circuit. Simple circuit analysis would provide enough evidence that the voltage is only rectified from AC to DC. A simple calculation of DC volts divided by AC output would prove that it’s simply close to peak positive voltage. A doubler requires two capacitors replacing two of the diodes in the rectifier.

[bschifke]

Thank you for your helpful reply Martin!

[LOUDthud]

342VAC through a Voltage Doubler would be nearly 1000V with no load.

Part of the confusion comes from the fact that most schematic software won't let you draw diodes at 45 degrees and most of the "Mouse Jockeys" (formerly called draftsmen) that draw the schematics don't understand the circuits they are drawing.