Mojotone British 800 2204 clone---- crazy voltages

[armandodiaz]

Thanks for everyone's help!!!!!!!

 

[armandodiaz]

THanks for everyone's help!!!!!!

 

[ThreeChordWonder]

Those small probe points on the back of the chassis, if connected to pin #8 on each EL34 socket, and with a 1 ohm resistor between pin #8 and ground are a great idea.

Unless you do something really stupid, the probe points will only see millivolts and milliamps.

You can probe them with a digital multimeter to measure the voltage drop across the resistor (between pin 8 and ground) and that gives you a direct analogue measurement of the bias current. Ohm's Law, Voltage V = Current I x Resistance R reduces to V = I when R = 1. So if you see a 35 mV drop across the resistor, you have a 35 mA current.

Far safer IMHO than going prodding around inside a live chassis.

What I would not do, for sure, however, is to put probe points in for any of the high voltage points.

 

[NickKUK]

Those small probe points on the back of the chassis, if connected to pin #8 on each EL34 socket, and with a 1 ohm resistor between pin #8 and ground are a great idea.

Unless you do something really stupid, the probe points will only see millivolts and milliamps.

You can probe them with a digital multimeter to measure the voltage drop across the resistor (between pin 8 and ground) and that gives you a direct analogue measurement of the bias current. Ohm's Law, Voltage V = Current I x Resistance R reduces to V = I when R = 1. So if you see a 35 mV drop across the resistor, you have a 35 mA current.

Far safer IMHO than going prodding around inside a live chassis.

What I would not do, for sure, however, is to put probe points in for any of the high voltage points.

Unless scaled down to mV using a voltage divider and a low mA fuse inline.
9M/1Mohm divider can be useful.