![]() It's also not quite as accurate since bypassing the OT does change the circuit very slightly and increase the measured current. expect fireworks - I did once destroy a quite nice little multimeter doing this, simply by slipping with one of the probes. There is an even quicker and more dangerous method which involves using the meter as a current meter across the OT primary ('transformer shunt method'), but I really don't recommend this as not only is it equally dangerous to you, it's more dangerous to the amp (and the meter) if you get anything wrong, since the meter is then nearly a dead short across the amp's HT supply. Then divide the voltage by the resistance to get the current.īut DON'T try this unless you're absolutely sure you know what you're doing. The voltage you are expecting to read is in the few volts at most, even though the voltage to ground is much higher. You must measure the resistance of the primaries (best to check both sides since they are not always exactly the same) with the amp off, then it's best to clip the test probes to the points you need (OT center-tap feed and tube pin 3, plate connection) and only then power up. But it is DANGEROUS since you're connecting to two points which are both at over 400V relative to ground. This is actually the best and most accurate method, since it avoids including the screen current and does not alter the circuit in any way.
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