Operating the VK-75
Normal operation of the VK-75 requires simply turning the unit on. There are no meters
to connect, bias setpoints to remember, or drifting bias points to adjust. Please read the
Autobias Feature section for more details.
Turning the VK-75 On:
The power switch is located at the rear of the unit. When you turn the unit on, it will go
through a gentle power-on sequence. After about one minute, four LED’s visible from
the top of the chassis should light up. This indicates that full operating bias has been
reached and the unit is now ready to play.
Turning the VK-75 Off:
The unit can be turned Off at any time (even while playing). If needed, please wait at
least 30 seconds before turning the unit ON again.
Autobias Feature:
The VK-75 implements a sophisticated autobias circuit that automatically compensates
for tube aging and line voltage fluctuations, as well as marginal mismatching of tubes.
The successful operation of the autobias circuit is noted by individual LED’s that glow
visibly next to each output tube when viewed from the top of the chassis. A total of four
LED’s should light up to indicate proper operation of the circuit. If one of the LED’s
fails to light up (after the unit is warm),
there could be two reasons for this problem:
1. The particular output tube is defective. In this case replacing this tube with a
known good one should turn the LED ON.
2. The amplifier was overstressed and the protective fuse inside opened. These
fuses protect output tubes from overloading. There are four fuses mounted on the
two PC boards. Please refer to the section on replacing fuses for correct
procedure.