WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Руководство пользователя

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20 W Stereo Audio Amplifier
builder to bring up the ac line voltage slowly while monitoring the current for excessive
draw. In the steps that follow, do not install any tubes until instructed to do so.
Remember that dangerous voltages are present. Be extremely careful. As a safety measure, do
not work alone. Do not let the amplifier run unattended until all preliminary tests have been
successfully completed.
Set R418 (the bias sense potentiometer) on the power management expansion PWB fully
clockwise (of not already set there).
10) Insert the rectifier tube, V51 (6CA4). Attach the ac power connector to the back panel
receptacle. Insert the ac power supply cord in an outlet. Switch the power on. The pilot lamp
should light and the filaments on V51 should be visible. Let the amplifier run for several
minutes while observing for any unusual behavior. Be very careful as high voltages are
present in the circuit.
Important note: Run the amplifier in this condition (B+ present but no amplifier tubes
installed) only long enough to complete the checks specified here. Long-term operation with no
tubes present other than V51 can result in component damage.
For reference, the following series of events occurs at power-on, listed below in order:
• Power from the front panel On/Off switch (SW51) energizes relay RYL202 on the power
management PWB. This applies power to transformers T51 and T201.
• The start-up time-delay interval begins, determined by R211 and C207 on the power
management PWB. This interval is approximately 30–60 s.
• Rectifier V51 warms up and begins applying B+ power, which is sensed by the voltage-
monitoring circuit of Q204 and Q205 on the power management PWB. Within about 15 s,
the B+ voltage has built up to 400 V dc, which energizes relay RYL205.
• The bias voltage ramps up to about –30 V or so, which is sensed by the Q404 circuit on
the power management expansion PWB. This energizes RYL402, which is part of the
interlock loop that also includes SW401 (the cabinet cover switch). Note that SW401 is
bypassed during tests and measurements.
• After the start-up time-delay is reached, the auto-off and interlock loop (B+ sense,
temperature sense, and bias present sense) circuits are enabled by the combination of
RYL203 and RYL204.
A failure in any of the previous steps will remove power from the amplifier.