4.1.6 Asymmetry Switch
The asymmetry switch raises the bias and threshold of the negative or positive side of the
detector depending on the position of the switch.
4.1.7 Sidechain Highpass Filter
The Sidechain HPF applies additional resistance across the detector input coupling
capacitors effectively creating a first order highpass filter. The filter is disabled through a
switch when the filter control is set at minimum.
4.1.8 Output Attenuator
The Output Level is implemented immediately after the output transformer. The Output
control is integrated into a T-Pad that provides proper loading to the output transformer
and attenuates the output to the required user setting.
4.1.9 Test Facilities
The Retro 176 has an integral balance testing system. The static test injects a common-
mode 60 Hz signal into the push-pull amplifier. The dynamic test injects a dc voltage
with 60 Hz component to observe balance during gain reduction. It allows the technician
a way to balance the amplifier without test equipment. See the Aignment and
Maintenance section for procedures.
4.3
Power Supply Circuit Board
4.3.1 Mains Input
The AC Power enters the 176 through the IEC power receptacle. It travels to the fuse,
the door interlock switch and the front panel User Power switch. Finally it reaches the
Voltage Selector switch and the Power Transformer.
4.3.2 Power Transformer
The Power Transformer provides several voltages that are used in the 176. It has
additional shielding and low losses to operate cool and efficiently. It accepts 120 or 240
Volts at 50/60 Hertz. It provides 5 Volts and 600 Volts to the high voltage rectifier. It
also has a center-tapped 6.3 Volt 3 Amp output for the amplifier tube filaments.
4.3.3 5Y3 High Voltage Rectifier
The 5Y3 is a commonly available full-wave power rectifier. The original design used a
5AR4 that can also be used and provides a slower turn-on to allow the filaments to warm
up. A common failure is arcing in the tube, which can blow the power fuse.
