WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Руководство пользователя, Страница: 145 / 194

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20 W Stereo Audio Amplifier
Note that typical operating voltages are shown in Table 6.3 and Figure 1.1 with a bias setting
of –30 V dc. These operating voltages will vary somewhat depending on tube characteristics and
variations in the ac line voltage.
29) Switch the amplifier off. Remove the power cord from the ac outlet.
30) Using a voltmeter, check the B+ supply voltage to confirm that the voltage at the B+
terminal 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.
31) After the tubes have cooled, install the shields on V1 and V4.
32 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)