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k150-8 [message #14395]

Fri, 24 September 2010 13:11

Bill
Messages: 64
Registered: March 2002
Location: Kansas

Member

I bought a k150-8, non working, pilot light works, no sound at speakers. Found someone had reversed the monitor and speaker outputs on the output board, wired the speakers as a short. I fixed these things and now have signal all the way through the amp, but it has a whoop-whoop-whoop sound, that is not affected by the volume or other controls,puts out about 20 volts ac--don't see any dc. Someone has replaced one driver with an SK3024, and the thermal diode was replaced by a 116 diode, and not placed in the chassis heat sink. Three other transistors have been changed on the premap board. I will try to isolate where it's coming from--either preamp or power board first.
Bill C

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Re: k150-8 [message #14398 is a reply to message #14395]

Fri, 24 September 2010 14:37

Bill
Messages: 64
Registered: March 2002
Location: Kansas

Member

Update on the k150-8 project.
With all boards installed normal, I have 89.3.vdc at the power iputs of the board. Voltage at the preamps is 9.5v on the red/positive side, and 3.87 volts on the negative.

With the power cut off the right preamp it is 10.62v positive and 2.76 vlots negative.

With both preamps cut off it is 12.56 volts positive and 1.4 volts negative.

Looks like I have a power regulator problem, too.
Bill C

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Re: k150-8 [message #14399 is a reply to message #14395]

Fri, 24 September 2010 14:49

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

That's strange that the negative supply gets lower as you unhook more load from it.

I guess you're right that there is a problem in the regulator circuit. As I recall, the positive supply is set by the circuit values, and the negative supply tracks the positive supply. I'd check the transistors and the tantalum caps in there first.

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Re: k150-8 [message #14403 is a reply to message #14399]

Fri, 24 September 2010 17:31

Bill
Messages: 64
Registered: March 2002
Location: Kansas

Member

Thanks Bill,
So far I've only found the second driver was bad, so replaced that, and went ahead and put in the correct thermal diode (1n3754). Will try the power board now and see what changes.
Have a good weekend, and thanks for your help.
Bill C

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