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Old 21st Aug 2013, 10:01 pm   #15
Herald1360
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Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
Default Re: Roberts R200- Distorted Output

Hi Josh,

what were those voltages measured against- Batt+ or signal ground?

I would expect to see about 23mV across the output emitter resistor for a 4mA standing current.

The bias problems with replacement devices could just be down to the new transistors being "better" ie less leaky than the original types, thus needing some actual negative bias between emitter and base to turn them on. It wasn't unusual for pnp germanium output transistors to need positive bias to actually turn them off.
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