Re: Repairing my Tektronix 454 oscilloscope need some advice

Chuck Harris
 

Wonderful! I just wanted to be sure that you and others were
aware of the issue.

Also, many of these HV diodes are designed to be used in old
color TV's, and CRT type monitors, so they need to be faster
than they would for the old style of transformer driven microwave
oven.

New style microwave ovens use inverters, and as such could be
pretty high frequency... I have never taken one apart.

-Chuck Harris

Ernesto wrote:

Hi Chuck,

You are very right about the importance of the diode recovery time. The specification on Amazon for this cheapy diode is Trr = 100 nS maximum. Other "fast" HV diodes specify 60 or 70 nS, not a big difference.
At 50 kHz the period of the rectified sine wave is 20 mS, 200 times longer than the Trr. During these 100nS the peak of the sine wave will barely comes down, so the operation should be safe. Indeed when I installed these diodes the efficiency of the supply increased, and it behaved correctly.

- Ernesto



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