Quicksilver ships the Sixty Watt Mono Amplifiers with matched KT88 tubes but many different output
tubes can be used. The output tubes should be matched.
Output tubes will need to be replaced periodically. When a degradation in sound occurs, the fuse blows
repeatedly, or the tubes will not hold their bias anymore, it is time for new output tubes. We
recommend purchasing tubes from Quicksilver Audio or your dealer and we recommend keeping extra
fuses and an extra output tube on hand.
OUTPUT TUBE BIAS SETTING
Output tube bias should be set immediately when new tubes are put in; then again in 15 minutes; and
periodically the first few times of using the amplifiers. After that the bias should be checked monthly.
The bias control is located between the output tubes near the power transformer.
To adjust the bias you will need a slot-head screwdriver and a multimeter that reads millivolts. Adjust
by turning clockwise to increase bias; counterclockwise to decrease bias.
Set the meter to read millivolts and insert the black and red probes from your meter into the black and
red pin jacks on the amp. The millivolt reading on the meter is actually the sum of the bias currents
through the 2 output tubes. Efficient speakers will sound better with lower bias (60mv) and inefficient
speakers may require higher bias (80mv.) Bias should not be set higher than 100mv.
If the bias cannot be set low enough, then an output tube may be shorted and the amplifier should be
turned off immediately. If the bias cannot be set high enough, then one output tube may be dead. In
either case, the output tubes need replacing. Replace the output tubes as matched pairs—matched pairs
will sound better and last longer.
POWER SUPPLY
CAPACITOR
INPUT
TUBE
12AX7
DRIVER
TUBE
12BH7
OUTPUT TUBES
INSERT METER PROBES
TO CHECK BIAS
OUTPUT
TRANSFORMER
POWER
TRANSFORMER
INPUT
CONNECTOR
100k
SPEAKER
TERMINAL
POWER
CORD
3 AMP
FUSE
POWER
SWITCH
Push in at
top to turn
on
8
C
4
Quicksilver Audio Sixty Watt Mono Amplifier
Bottom View
