KR-6170 Idle Current Adjustment

tinkerer

AK Subscriber
Subscriber
Repaired the left channel on this receiver KR-6170. I would like to check/set the Bias/Idle Curent. The Service Manual I found online is a bit confusing. Is anyone familar with the Bias/Idle Current setting procedure?

KR 6170 Adjustments.jpg

I have checked the voltages as described above under Testing Procedures. Voltages seem to be acceptable. Q2: 68.8 VDC, Q3: 31.1 VDC, Q4: 31.7 VDC, Q5: 68.8 VDC.

The Idling Current procedure on the right side has me a bit confused. It says to test at collector of transistors. I'm familar with testing across emitters or emitter resistors but not across collectors. I tried testing with 1 probe on the collector of Q2 and the other probe on the collector of Q3 and got a pop in the speaker and it blew the fuse in the DVM. The DVM was set on 200mA. I did not have a dummy load, audio generator, or oscilloscope as described in steps 1 & 2. The instructions make no sense to me.

The receiver plays and doesn't sound too bad The TO3 outputs don't seem to be running hot, so the original settings on VR1 VR2 must be in the ballpark.

Anyone willing to make suggestions?

Thanks
 
Cap coupled amp.
Having the test equipment is a way to watch the trace for any distortion but not critical. The DMM and your ears are all you'll need.
The set can be on the DBT when adjusting the trimmer for the idle.
Measure the voltage at the output collectors as shown. Red probe to the output case and the Black to the chassis, your meter set to DC volts.
Set the middle outputs using the trimmer to half the voltage of the outer outputs. (The house line voltage is going to change the voltage from what the SM says. So measure the outer output and set the inners for half the outers)
You'll see how it works once you start the procedure.
Note:
The case of the output is the collector.
The setting is important but not as critical as the push/pull style circuitry. A little more forgiving with extra heat (when sound is heard) as a by product of an incorrect setting.

I have a Kenwood KR-6160 and like it more than the Pioneer 770's I know well.
 
Last edited:
zebulon1 Thanks for the reply.

I tested per your instructions, but adjusting the trimmers yielded very little if any change in voltage. A 1/8 turn of the trimmers in either direction maybe changed the voltage +- .1 VDC. Having experienced large changes of voltages in the past with small adjustments in trimmers I didn't want to press my luck so I returned the trimmers to their approx original settings and let them be, taking petehall347's advice. I also tested some voltages on the amp board and everything was within 5 -10%. As I stated before the amp sounds decent considering there are still mostly original transistors and caps on the amp board, as I did not perform a complete rebuild. And the outputs don't run hot.

I did discover arcing in the on/off switch contacts, which I sanded lightly. That cured an issue with the lights fluctuating under moderate volume.

All things considered I'm satisfied.

Thanks petehall347 for your input.

Cheers........Jim
 
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