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Old 11th December 2014, 05:48 PM   #1
DavidJE is offline DavidJE  United Kingdom
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Default Power supply load testing

I've recently acquired a vintage valve based bench power supply that has a variable 0 to 300V DC output, a fixed -150V DC output and a fixed 6.3V AC output. I'm hoping to use it for developing and testing valve circuits which I'm guessing is what it was intended for when it was made in the 60's.

The unit has four selenium rectifiers which I want to replace and I also want to make sure that the outputs produce the voltages that they're supposed to. So I'm thinking about using some kind of dummy loads on the DC outputs while I measure the voltages.

The -150V output should be fairly simple as it's a fixed voltage rated at 7mA. So I'm guessing that I can just use Ohms Law etc to calculate that a 22K resistor that can safely dissipate 1W will suffice? Is that correct?

The 0 to 300V output is a bit more tricky as it's just rated at 60mA. I'm guessing it won't be able to supply 60mA at every voltage between 1 and 300V. So I'm not sure if I should assume that it's 60mA at 300V and use a 5.1K (very high wattage) or something else.

What would be the best approach?

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Old 11th December 2014, 06:04 PM   #2
DF96 is offline DF96  England
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I would buy a small set of power resistors for checking the 0-300V output. You will want to check behaviour at several different currents and voltages.

2x 10k 15-20W (use in series or parallel)

2x 3.3k 10W (use singly at lower voltages and in series at higher voltages)
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Old 11th December 2014, 11:23 PM   #3
DavidJE is offline DavidJE  United Kingdom
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Thanks, that makes sense. I'll do the same for the -150V output too.
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