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Old March 17th 18, 07:44 PM posted to
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Default KLH Model 21 help

On 17/03/2018 1:22 AM, wrote:
> On Friday, July 27, 2001 at 2:34:43 PM UTC-5, MitchSF wrote:
>> Hi, I'm almost finished restoring a KLH Model 21. I replaced three
>> transistors on the RF board and it now works!
>> The only problem left is a hum from the audio board. I
>> disconnected it from the input to the board so I'm sure it's not
>> coming from anywhere else. I replaced the filter capacitor and all
>> electrolytics on the audio board and it's a little quieter, but
>> still there. The level of the hum doesn't change with the volume
>> control.
>> Any hints would be appreciated!
>> Thanks, Mitch

> Hi Mitch. The power supply filters, either of the black color
> are/were a common failure item. They should be replaced. However,
> note that the positive terminal was marked with the stripe as we
> would now associate with the negative terminal. It is also important
> that you do not increase the value of these capacitors as the power
> supply can't handle the extra in-rush and operational paramete5rs.
> Mark - Former National Service Manager, KLH Cambridge.

Wonder whether he even still has it 17 years later? :-)