CLASSIC 25
Line-up Procedure.
The Amplifier will need the Output Valves replacing after many thousands of hours
use. Usually the valves will eventually decline with age and this is the point when the
valves need replacing.
For best performance it is best to obtain matched-pair valves as replacement.
To replace the valves, simply remove the old valves by pulling the vales out of their
sockets and replacing with new valves by lining up the pip on the valve with the
socket. Usually twisting the valves around lightly in the socket until they engage with
the pip is acceptable.
The valve is then pushed home into the socket carefully.
FOR EXPERIENCED QUALIFIED PERSONS ONLY.
If you have the necessary test equipment, then remove the top plate from the
Amplifier to expose the circuitry.
EXTREME CAUTION is required as there are FATAL VOLTAGES within the
Amplifier unit.
Adjust the trimmer resistor R with a trimmer tool to obtain true linearity of a
sinusoidal waveform as measured on the Loudspeaker terminals whilst connected
into an 8 ohm dummy load.
This is best done by applying a 1 KHz sine wave to the amplifier input and increasing
the input level until the amplifier goes into clipping.
At this point adjust R to obtain balanced clipping on the peaks.
Adjustment for balanced waveform.