25
FINAL INSPECTION
Visually inspect all connections and wiring comparing against the master charts and manual.
Rotate all four bias adjust controls located on the rear of the chassis (V7, V8, V9 and V10) fully
clockwise for maximum bias. A.C. balance potentiometers between KT88/6550’s should be set in the
mid-position.
Install 8 Amp fuse in fuse holder.
Install 12BY7A tubes. (V1 thru V6).
Install KT88/6550 output tubes (V7 thru V10).
Set Meter selector switch to “OFF” position.
If an ohmmeter is available check all points in the resistance chart.
NOTE: In order to insure accurate meter readings, the amplifier must be placed in its normal operating
position.
A WORD OF CAUTION. OPERATING VOLTAGES IN THIS UNIT ARE AS HIGH AS 450
VOLTS AND ARE DANGEROUS. ONCE THE AMPLIFIER IS TURNED ON, BE EXTREMELY
CAUTIOUS WHEN TAKING READINGS OR MAKING MEASUREMENTS.
Insert the A.C. line cord into a 117 volt 60 cycle source. The tube filaments should light. Allow the
amplifier to warm up for approximately one minute.
IF THE KT88/6550 OUTPUT TUBES BEGIN TO GLOW CHERRY RED DISCONNECT THE
A.C. LINE CORD AND INSPECT THE AMPLIFIER FOR TROUBLE.
TESTS AND ADJUSTMENTS
Rotate the meter bias selector switch located on the rear of the chassis to the V10 position. The meter
should deflect upscale, but should be below the “BIAS” alignment mark. Switch through V9, V8 and V7
positions and the readings should be similar. At this point you may assume that the power supply has
been correctly wired and that the KT88/6550 output tubes are being biased.
IF THE METER DEFLECTS BEYOND THE “BIAS” MARK OR IF THERE IS NO DEFLECTION AT
ALL, DISCONNECT A.C. POWER PLUG AND RECHECK WIRING.
D.C. Bias Adjustment:
Allow the amplifier to warm up for an additional ten minutes before performing the following adjustments.
These adjustments must be done without an input signal (phono or tape program source) feeding the amplifier.
This operation establishes the D.C. quiescent point of the tubes.
Set the meter selector switch located on the rear panel to the V10 position.
Using a screwdriver adjust the V10 bias potentiometer until the pointer is exactly at the “BIAS”
mark.
Repeat this procedure for adjusting V9, V8 and V7, rotating meter selector switch to correspond
with appropriate screwdriver adjustment positions.
Repeat this procedure until no change in the meter setting is noticed as the meter selector switch is
rotated through the various positions from V10 through V7.
For approximately
½
hour after you have made the above adjustments keep a constant check on the
meter reading. This should be done every few minutes by rotating the meter selector switch through
positions V10, V9, V8 and V7. At each position check the meter to see that the rea ding has not gone
above (to the right of) the original bias setting. If any of the original settings have changed, re-adjust
the corresponding bias adjustment so that the meter again reads at the proper bias mark.
The output tubes have now been adjusted to their proper operating points.
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