WhitakerAudio J C Whitaker 20 W Stereo Audio Amplifier, Manual

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20 W Stereo Audio Amplifier
• Read the value displayed on the ac voltmeter. Determine the power as follows: P = E
2
/ R ,
where E = the voltage measured by the audio voltmeter and R = 8 (the load resistance).
For this amplifier, the voltage measured is typically 10 V, which translates to 12.5 W. This
is the maximum operating point of the amplifier.
Check one channel, and then the other. Note that the peak power available from the amplifier
will tend to decrease as the output tubes age. The input line voltage will also impact the output
power. All measurements described in this User/Assembly Manual are with an input line voltage
of 120 V ac.
7.1.4 Crosstalk
Crosstalk is a parameter that identifies the amount of signal applied to one channel that may
appear in the other channel. This parameter is not specified in Table 7.1 since nearly all stereo
material has a high correlation between channels. In any event, it may be measured as follows:
• Connect a suitable resistive load to each channel. Set the Volume control fully clockwise.
• Apply a 1 kHz signal at 1.0 V rms to the right channel input. (This will result in about 10
W output.) Connect an audio voltmeter to the right channel output. Adjust the meter to
read 0 dB on a suitable scale.
• Move the 1 kHz signal to the left channel input. Place a shorting plug in the right channel
input jack.
• Using the audio voltmeter, measure the residual signal, which will be a combination of
noise and crosstalk from the left channel into the right channel. A reading of
approximately –85 dB is typical for this amplifier.
• Return the audio voltmeter sensitivity switch to the previous setting (10 W). Connect the
voltmeter to the left channel output. Adjust the meter to read 0 dB.
• Move the 1 kHz signal to the right channel input. Place a shorting plug in the left channel
input jack.
• Using the audio voltmeter, measure the residual signal, which will be a combination of
noise and crosstalk from the right channel into the left channel. A reading of –85 dB is
typical for this amplifier.