WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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28) If an ac ammeter is available, measure the current pulled by the amplifier from the ac line.
With an ac input voltage of 120 V and no audio input, the current draw should be
approximately 800 mA for a bias setting of –30 V.
29) Switch the amplifier off. Remove the power cord from the ac outlet. Using a voltmeter,
check the B+ supply voltage to confirm that the voltage at terminal #1 of TB4 on the left
channel PWB has decreased to zero. Carefully check for component heating under the
chassis. Some components may be warm, but (other than the vacuum tubes) they should not
run hot.
30) After the tubes have cooled, install the shields on V1 and V4. Remove the mounting screws
and mount the shields.
31 After the preliminary tests have been successfully completed, measurements should be taken
on the amplifier as detailed in the next section.
Note: The amplifier should be operated only with its rated load applied. Operation into an
open-circuit or short-circuit load can result in damage to components .
6.1 Power Management System Issues
Operation of the power management system is essentially invisible. As long as any of the trip
points are not present, the overall system will perform as expected. If specific tests on the power
management PWB are needed, the following tests may be run. Use extreme caution in the
following steps as high voltages may be present.
Many checks on the power management PWB can be done with the board in place. Power to
relays can be determined by measuring the voltages present on the foil side of the board. The
V51,
6CA4
1 400 V ac
2 0 V
3 350 V
4 6.3 V ac Measured with respect to pin #5 (heater)
5 6.3 V ac Measured with respect to pin #4 (heater)
6 0 V
7 400 V ac
8 0 V
9 0 V
Table 6.3 Typical Voltmeter Readings
(readings /–10% can be considered normal)