[Heath] AR1250

[Georges Puttemans]

Dear,

The problem with the amplifier part of the AR1250 is a well known common
problem I assume.

I have build one for another person and regularly he called me when his
receiver got to warm and dropped down.

Nothing is or ws wrong or defective in the receiver and finally I've found
a simple solution.

In the manual they tell you to adjust the bias voltage to 12mV.
Well that's the problem.

Just act as follows:
- adjust the bias as described in the Manual, then:
- connect 2 resistors of 8 Ohm and 50 Watt at the output (speakers)
terminals,
- put in a signal of 400 or 1000 Hz into one of the inputs and regulate the
input signal and volume control to obtain at least 20W output, not 30W, 20W
is about 12.8 V
- wait for about 30 minutes, the power transistors will become very hot,
- now turn off power for just a few seconds and connect a very sensitive
voltmeter to measure the bias voltage, or just connect him at the very
beginning,
- now regulate the voltage not at 12mV but at about 6 to 9mV
- let the receiver cool down,
- do the same procedure over and look at the bias and feel the heath at the
power transistors.
This must be much lower now, if not reduce the bias voltage a little lower.
This must solve the problem.

Note, except if you have 2 simular Volt meters, one have to do this
procedure twice, ones for each channel of course.

Succes.

Best regards.
Georges Puttemans.
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