I have bias a couple of vintage amps/receivers and basically relied on the service manual to bias the amp, basically I measure the current between two test points and set the bias at a certain current as recommended by the manufacturer, wait 10-15 minutes and check if the current has drifted and adjust accordingly. Recently I acquired a Usher R1.5 power amp, it is a high bias amp, delivering 50 watts Class A and 150 at Class AB. No service manual was available, searching the net, I got a lot of recommendations to bias the amp until the heatsinks gets a temperature of 50c after idling for an hour. Apparently this is the recommended setting for Class A and high bias amps. Is there recommended heatsink temperate for Class AB amps?
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Class AB amps should be biassed to run cool. Their heatsinks reaching 50C under a fair bit of load.
Some commercial amps need care. My experience is with consumer amps, HT receivers where heatsinks are undersized. They tend to be under biassed and following the manual is not good. The rule of thumb for Class AB depends on the output stage. Mosfets do better higher biassed for sure. Bipolar with EF outputs want 26mV drop across their emitter resistors.
Some commercial amps need care. My experience is with consumer amps, HT receivers where heatsinks are undersized. They tend to be under biassed and following the manual is not good. The rule of thumb for Class AB depends on the output stage. Mosfets do better higher biassed for sure. Bipolar with EF outputs want 26mV drop across their emitter resistors.