PSU test load (was: My PDP11/23 arrived...)

On Jan 24, 2012, at 6:11 PM, Richard wrote: I start with the current required. If there's a minimum load current specified, I'll start from that and go up, otherwise anywhere from 1/4 to 1/2 the maximum current specified. From there I figure out what resistance I'll need for the voltage rail operating normally, and then spec a resistance (sometimes multiple series or parallel elements) which can withstand from 3-10x the power dissipation (especially in case the supply is wildly out of spec on the voltage). I have some dummy load resistors for tube amp power supplies that are like small ceramic paper towel rolls with wire wrapped around them (the 8 ohm one for the speaker load is especially impressive, though since it's fairly reactive, it's also not a great speaker load). They're rated at something like 150 watts, and I think even that might be with forced air through them if you're running them longer than about a minute (which I don't). - Dave