Multimeter testing at higher voltages

I needed a way to test out my HP 3478A multimeter at higher voltages. I ended up driving a transformer with a signal generator, then running the output directly into a voltage doubler. IMG_0772

Unfortunately the reverse breakdown of 1N4148 diodes is only a little bit above 100V. The solution (as seen above) is to simply run a few in series. I used a ceramic capacitor on the input, and an 0.47uF X2 rated filter capacitor on the output. Not really designed for high voltage DC, but it did the job! I was able to squeeze 426Vdc out with effectively no load (10M ohms).

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Lowering the amplitude from the signal generator gave me the 300V max the 3478A will take:

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Conclusion: It isn’t too hard to generate high voltages with readily available parts, and my 3478A works as expected. I didn’t even electrocute myself! Seriously though.. a little caution goes a long way.

Just a little dust..

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I found the inside of an Agilent 33120A looking like this. It runs a little warm without being covered in a blanket of dust! No wonder the output amplifier failed.