Friday, March 30, 2018

Measuring Your Voltages: Why To Do It.

A relatively new Blues Junior III came in the other day because it wasn't making any sound....not a peep.

The first thing I did after testing the power tubes was get out my trusty multimeter I got from Horror Freight and started measuring voltages on the power tubes. Lemme see, plate voltage OK. Bias voltage OK...where the hell's the screen voltage?

Dave's not here, man.

It seems that  R47 (I think) the 2.2k 2 watt resistor in the power supply string had failed open kinda like a self activated standby switch.

From there it was a couple of hours work to crack it open, get rid of the Illinois power supply capacitors and replace the suspect resistor.

It powered right up and all is good.

The point is, measuring voltages is the first thing you do. Had I not done so I'd probably still be throwing parts at it in a random fashion hoping that something would stick or give me a clue.


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