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Enzo is right on about the tubes glowing and they should all be lit. We need to isolate the problem and find out why one is not lit whether it's the tubes or the socket or a problem with the circuit which is what usually happens when a tube shorts with this amp. Let me explain a few things first about your meter and how the bias works on that amp. When you say AC & DC Amps that's exactly what it is but measuring voltage and Amperage are two different things. To measure amperage you have to get in between the circuit to measure it where voltage and resistance you can measure across it like across a resistor you can measure the voltage and sometimes it's resistance of the resistor iif it's not in parallel with something else. You can't measure current across that resistor with your meter you would have to break the path and insert the leads in between them. You also have to move the red lead to the amperage side of the meter that says (A) for amperage. Those test points on your amp are for DC millivolts and what it is reading is a voltage across a 1 ohm resistor that is calculating how much amperage the tube is drawing as a 1 to 1 ratio where 1mv=1ma of amperage. So if you put your black lead in the middle pin and the red lead on the left pin and put your meter on DC milli volts you will read a combination of two tubes worth of milivolts of around 70 or 80 ish millivolts. Before we do this though we need to get all four tubes lit so try swapping a tube and see if it lights up.
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So this will REALLY show my ignorance but...Originally posted by Bruce / Mission Amps View Post
So if this tool can do 2 tubes at a time what about the other 2? Do you not have to set them all at the same time?
Do you have to do biasing for the pre-amp tubes as well?
The only thing that exceeds my ignorance is my desire not to be ignorant.
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plug your dummy load in but leave off plugging in signal to the amp when setting up the bias volts...Experience comes with more understanding
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