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KR-10000: no bias reading in one channel, but it plays fine

Raccoon1400

Raccoon1400

Super Member
When this unit came to me, the TO-3 outputs had been replaced with TO-3P. I swapped them out for Onsemi TO-3's. I set the bias in one channel to 45mV, but I don't get a reading in the other channel unless I am listening to it, and then it is in the 10-30mV range.
Maybe this is a result of collateral damage that was not repaired when the original outputs blew? Where should I start looking?

The last person in here made a mess of the thing. They rectified the voltage for the lamps, giving it 20VDC instead of 8VAC, blowing all the bulbs, to name one example.
 

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You are checking the voltage between the emitters of the output transistors?

What are the standing emitter voltages for each output transistor (referenced to chassis ground)?
 
Watthour said:
You are checking the voltage between the emitters of the output transistors?

What are the standing emitter voltages for each output transistor (referenced to chassis ground)?
Click to expand...
Yes, the voltage between the emitters.

In the good channel, the emitter to ground voltage of the NPN output is 40mV. It reads 0 for all other outputs.
 
Raccoon1400 said:
Yes, the voltage between the emitters.

In the good channel, the emitter to ground voltage of the NPN output is 40mV. It reads 0 for all other outputs.
Click to expand...
No...bias current is measured (on a common-collector-type output) NPN emitter to PNP emitter (this is measuring across the emitter resistors). NO reference to ground, since any offset will skew the reading.
 
EchoWars said:
No...bias current is measured (on a common-collector-type output) NPN emitter to PNP emitter (this is measuring across the emitter resistors). NO reference to ground, since any offset will skew the reading.
Click to expand...

This is what I did originally, following the instructions in the service manual. I successfully set the bias in one channel, got no reading in the other.
 
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