WhitakerAudio 60 W Stereo Power Amplifier, User And Assembly Manual

Page: 89 / 154

89
60 W Stereo Power Amplifier
6 Initial Checkout
Before performing the following steps, review the safety precautions given in Section 9 of this
manual.
After the amplifier has been assembled, the following steps are recommended to confirm
proper construction:
1) Remove ac power from the amplifier (unplug the ac line cord).
2) Remove all tubes.
3) Connect the ac line cord to the chassis. Do not connect the amplifier to an ac outlet . Using
an ohmmeter, check the resistance between the ground terminal and either line terminals.
Flip the front panel power switch and recheck. A reading of infinity should be found. If any
resistance is measured from ground to either line terminal, proceed no further. Recheck all
primary circuit connections.
4) Measure the resistance between the line terminals of the ac cord. It should be a high value
with the front panel power switch Off (due to VR3, typically greater than 300 k
Ω
) and
approximately 6
Ω
when the power switch is On.
5) Remove the ac power cord from the chassis.
6) Using an ohmmeter, confirm that the resistance values listed in Table 6.1 are observed. All
readings are with reference to ground. Readings within ±5 percent are considered normal.
For resistance measurements that are influenced by filter capacitors in the circuit, the value
given is the minimum typical reading. Check the power supply first, followed by the right
channel and then the left channel.
Table 6.1 Typical Power Supply Circuit Ohmmeter Readings with Power
Removed and Tube Removed
Tube Pin No. Typical Reading Notes
V51, 5U4, rectifier 1 –
2 < 35 kΩ Varies due to filter capacitors in circuit (heater/cathode)
3 –
4 ~ 50 Ω Plate 1
5 –
6 ~ 50 Ω Plate 2
7 –
8 < 35 kΩ Varies due to filter capacitors in circuit (heater/cathode)