647A Calibrator Squeel


Howard Matthews
 

Folks - any information appreciated.

I have 5 647A scopes in various states from almost calibrated to
(one) parts unit. All the working scopes have an audible high
frequency squeel that comes from the calibator unit. Turn the
calibrator off, or to 100v DC, and there is no squeel. In all
positions that output the square wave, there is an annoying squeel.

OK, a lot of people my age cannot hear it - but my hi frequency
hearing is still pretty good. It sounds like maybe 10kHz, which is
strange since the calibrator outputs a 1 kHz square wave. Well,
maybe not completely strange if you count the harmonics of 1 kHz.

Questions:
1. Was this normal in new scopes, i.e. a design flaw?
2. Is this caused by a transformer in an oscillator circuit aging?
3. Is there any known cure?

TNX, Howard

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