[Trevor]

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? :-)

Trevor.