Re: 547 scope HV transformer problem. One practical solution.


 

Hi Morris,

Yes, the deflection factors, which I called the "gain of the CRT" is an inverse function of the high voltage, and I have taken this into account. It requires simple readjustments of the gain of the vertical and horizontal amplifiers. When all this is over I will care about finding good standards to calibrate the scope with. In the meantime I have made some more observations:

After being relieved with the good results of lowering the HV to 1500 V I decided to try out a "thermal enhancement".
After removing the plastic cover of the HV section, I placed over it an old PC supply whose little fan did blow mostly over the transformer. And here is what I got:

- With HV = 1500 V, the supply current raised slightly in the first minutes, then it stabilized. One and a half hours later it was still the same, and the supply was still running fine.
- With HV raised to 1655 V, the same happened and I ended the test after one hour.
- With HV returned to the nominal 1850 V, exactly the same happened. The HV supply DID NOT FAIL.

So the COOLING OF THE TRANSFORMER will solve the problem of my 547, which originally failed after running for about 10 minutes.

The easiest implementation of the cooling can be to drill holes in the cover right above the HV transformer and place on top a little fan (with a filter), blowing on the transformer with the plastic cover off.
But I don't like the aesthetics of the fan sticking out on top of the instrument, so I will do the cooling internally. A change from electrical engineering to industrial engineering, haha.

Cheers,

Ernesto

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