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I put these test points into my 5E3 so that I could check the plate voltage of each tube as well as the current across the bias resistor. Does anyone think the use of these tip jacks is unsafe? The black one on the left is just for ground, the next two red ones to the right are connected to pin 3 of each power tube, the last red one on the right is for bias current. The 400 volts going through those tip jacks kind of bothers me.
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external test points connected to plate voltage are not a good idea, as you suspect. On the other hand, a test point that connects to the positive end of a 1 ohm resistor that is inserted btwn the cathode (or main cathode resistor like you 5E3) and ground is safe. You only have millivolts on the test point, and even shorting the test point to ground would not damage or affect the operation of the amp. If you short the plate voltage test point you have a problem... -
And....you don't measure current "across the bias resistor". You measure plate/cathode current and use that reading with the plate voltage reading to calculate the tube's dissipation wattage.
EX: 468 (plate v) x .042 (42ma plate current) = 19.6wThe farmer takes a wife, the barber takes a pole....Comment
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Actually, the bias jack on the far right is for voltage across the bias resistor. It has no 1-ohm resistor attached to it.Comment
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