WhitakerAudio 60 W Stereo Power Amplifier, Руководство пользователя и по сборке

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resulting from the high voltages generated by the collapsing magnetic field of the transformers in
the circuit. The varistor is essentially invisible in the circuit until a predetermined voltage is
reached, at which point the resistance of the device decreases to a low value, thereby shunting the
transient energy. Attention to transient disturbances is critical for proper operation of solid-state
hardware; taking similar precautions in tube-based equipment is a good practice.
Heater power for the amplifier tubes and the rectifier are obtained from the 6.3 V and 5 V
secondary windings, respectively, on power transformer T51. Potentiometer R60 serves as a
“hum balance” control by placing a positive dc voltage on the heaters, derived from the output of
the power supply through a ladder divider, to minimize hum.
A grid bias supply of nominally –40 V is developed through a silicon rectifier and capacitor-
input filter connected to the bias supply winding of the plate transformer. A potentiometer at the
output of the supply (R61) is provided for fine adjustment of bias. Resistor R62 is included to
prevent adjustment of bias to a lower level that might be advisable for the amplifier. The range of
adjustment is in the neighborhood of –20 to –60 V dc. Test points are provided adjacent to R61 to
simplify bias adjustment.
Exercise caution when setting the bias. While a low setting may improve distortion
performance, it will also increase the idling current through the output tubes. If excessively high,
shortened tube life may result. It is recommended that the optimum bias point be identified and
then backed off (bias made more negative) by some amount (e.g., 5 V) in order to extend tube life
and reduce power consumption.
Since this power supply may draw a fair amount of current when working at high power
levels, it should be connected to a source of ac power that is capable of handling the load without
voltage sag due to loading or some other device on the circuit. The amplifier can certainly share a
15 A circuit with a preamp, tuner, phono turntable, and related devices. The unit should not share
an ac mains circuit with high-current loads such as heaters or other high-wattage appliances.
1.2 General Considerations
The 60 W stereo power amplifier chassis is somewhat cramped for space, but nonetheless quite
serviceable. The amplifier is also quite heavy. The handles included on each side of the chassis
are for more than just appearance. They are also necessary for moving the unit.