WhitakerAudio AM/FM Stereo Tuner 2012, Assembly & User Manual

Page: 103 / 166

103
AM/FM Stereo Tuner
6 Initial Checkout
Before performing the following steps, review the safety precautions given in Section 10 of this
manual.
After the tuner has been assembled, the following steps are recommended to confirm proper
construction:
1) Remove ac power from the tuner (unplug the ac line cord).
2) Remove all tubes.
3) Connect the ac line cord to the chassis. Do not connect the tuner to an ac outlet . Using an
ohmmeter, check the resistance between the ground terminal and either line terminals. Push
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 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 12
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.
Table 6.1 Typical Ohmmeter Readings with Power Removed and Tubes Removed
Tube Pin No. Typical Reading Notes
V1,
6BA6
1 4 mΩ
2 0 Ω
3 – Heater
4 – Heater
5 ~10 kΩ Varies due to filter capacitors in circuit
6 ~22 kΩ Varies due to filter capacitors in circuit
7 68 Ω