How should a jlh amp be set up for first time setting the bias and midpoint voltage? Should I have speakers connected and a preamp on with audio signal input? I have all 4 pots turned all the way down (clockwise) and am ready to do this but I'm scared..I don't want to blow another cap or anything this time 
If your output cap is right polarity and has the right value and voltage rating there should be no particular danger connecting your speakers up. If you are scared to do so pick up some suitably rated resistors matching the impedance of your speakers and use them as a dummy load.
Measuring midpoint voltage is quite easy. You measure from each rail to the + side of the output cap. Both voltages across the output transistors have to be equal.
Qcurrent is a bit more tricky. Would help to know what your circuit looks like
Measuring midpoint voltage is quite easy. You measure from each rail to the + side of the output cap. Both voltages across the output transistors have to be equal.
Qcurrent is a bit more tricky. Would help to know what your circuit looks like
I know, a chinese version, it's what I have
. I replaced all the 470uf caps since one blew up when hooking up power from a 12v 10amp psu. 
The board has 20k printed where the 204's are, which is a 203, but it came with 202's and 204's so that's what I bought and yes, they are installed correctly this time
From what I understand I set the mm to amp with the red pen plugged into the 10amp port, the red connected to + of psu, and the black pen to the vcc+ on the amp and then adjust Q to 1 amp each side?
Unfortunately it's not the same version as mine. The principle is the same however. For the midpoint voltage you need to measure base to emittor voltage on the power transistors.
Both need to be equal.
For the Qc, I would recommend putting a resistor in series with the psu and measure the voltage across it. Using ohms law turn that into current.
12VDC is a bit low for a classic JLH1969. You will not get full output of the amp.
Both need to be equal.
For the Qc, I would recommend putting a resistor in series with the psu and measure the voltage across it. Using ohms law turn that into current.
12VDC is a bit low for a classic JLH1969. You will not get full output of the amp.
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