The amp runned over 30 years like this, now there is a problem somewhere that make the BC640 to burn. Tell me if im wrong but there is probably something on the 18v negative rail shorted that take too much current for the BC640 and make it run too hot until it finish to burn.
Lift the emitters of the two regulator transistors and put 100R 1W in series.
Then you will be able to measure the drop and calculate current. A volt or so drop won't make any difference to the opamps
If I do the same but instead of using a 100R I use the DMM in serie on the mA scale I will get the current or Im better with your method?
I recommend that you never use your ammeter function, unless there is no other way to do a current measurement.If I do the same but instead of using a 100R I use the DMM in serie on the mA scale I will get the current or Im better with your method?
Inserting a low value resistor and measuring volts drop is far more effective.
If you have a meter that resolves 0.1mVdc, you can resolve currents down to 0.1µA with 1k0 resistor, or down to 1µA with a 100r resistor. Even a 1r0 resistor allows resolution down to 0.1mA
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