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In Reply to: RE: Need some trouble shooting advice please...... posted by vinnie2 on October 07, 2016 at 06:43:37
Yes, you can measure it with a meter, although I prefer to use a scope. Being able to see the waveform shape sometimes helps to identify the origin. A scope will also tell you whether it's oscillating, which sometimes sounds like hum. Modelling the PS can provide a lot of insight into how it's functioning and whether it's clean enough. Don't forget to apply a load that approximates the actual current draw. Be careful poking around in the PS with a scope. It's easy to exceed the voltage limits of the probe and/or scope input with tube circuitry. You might need to construct a voltage divider for this use or buy a high voltage probe.
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Buy Chinese. Bury freedom.
Edits: 10/07/16Follow Ups:
I tried hooking my scope up to an rca cable plugged into the RCA output of the preamp. I followed the instruction manual for getting a trace, but then didn't much of anything as a wave form on the scope. I really don't much about using it so I may be doing some thing wrong. Maybe I will try hooking my signal generator to the preamp and see if that helps at least get a sine wave or something I can recognize.
I thought you were referring to hum at the output of a power amp, not a preamp. What's the maximum sensitivity of your scope (V/div) with a 1:1 probe? Mine goes to 5mV/div, but also has a X10 multiplier switch for 0.5mV/div. Sometimes even that isn't enough to see preamp hum. One of these days I'll build a low noise SS preamp with 30dB gain for this use.
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Buy Chinese. Bury freedom.
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