Dynamic Headphone Amps
Schematic by Maurice Bénaya published in L'Audiophile n° 32 (March 95').
The output transformers for such usage are not very common, so a power transformer was
used as output tranny.
A high power model (80VA toroidal in M. Bénaya's prototype) is used to reduce distortion.
The formula to obtain the input/output voltages fos such a transformer is indicated on the schematic.
To avoid core saturation, we inject an opposite current of the same value in a second primary.
The 6CG7/6FQ7 output tube plate load, optimally 33K, should not go under 25K.
Resistor R2 (not absolutely necessary) adjusts the plate current to 4.5mA.
Resistor R1 adjusts the second primary current to the same value as the first one (which could be slightly different of the plate current !).
The use of standard power transformers gives a somewhat unusual power supply.
It's of course possible to use only one transformer with adequate windings (secondaries of 230V and 10V).