SomeThing is not right with the crosstalk numbers. Either your methodology is flawed, or there is a problem with your Mini3.   I would inspect the soldering on the Mini3 with a loupe. High resistance at the phone jack or ground channel amp could elevate the crosstalk numbers.

Hook up your voltmeter to the power and measure the voltage with the power supply connected to the amp, then slowly and carefully move your hand close to the mosfets and observe the voltage. DO NOT TOUCH ANY EXPOSED WIRES!!!

Disconnect the power supply from the amp and measure the voltage at the power supply plug.

^Looking good there Pierre.   The volume knob turned out looking pretty nice, I think.   Did you get the high power supply voltage down, or is it still running about 68v or so?   I would like to see about 12v to 13v across the heaters. I'm not sure how they will last with almost...

is your power supply rated for 110vac input or 220vac?  

It would be easier if you did what Nikongod asks.   Then post your findings.

Measure resistance between RCA signal input jack(the center pin) and circuit ground.

Check the resistance between the input RCA jacks and ground.   68v is a bit high for your power supply. Is it 48v dc or ac?

Allow the tube heaters time to warm before taking measurements.    

Measure between the grid and cathode for voltage.   Measure voltage between the gate and source on the mosfets.

Your power supply is 48v?

Check some voltages and compare the 2 channels.   Power down and check the resistance from input RCA jacks to the grids, and to ground. Again, compare channels.

Yep, wire according to the diagram you posted earlier, while looking at the bottom of the socket.

Nikongod is right. The sockets should be wired looking at the bottom of the tube. They are backwards.

Quote: You are not finished in this pic? It looks like nothing connected to pin 1(plate) and a wire going to pin 9(should not be a wire on pin 9)   Up close pics would help.  

how about pin 4 or 5 on the tubes. One should be about 12v and the other should be zero.

Check some voltages. Start at the power inlet.  Make sure the polarity is not reversed. My first guess would be cold solder joints.

If you are facing the part, the pins would be gate drain source, from left to right.

You double check the pinout on the mostest? The pinout on the devices does not match the pinout on your board.

Some of the power supplies struggle a little to fire up a cold amp, so the power supply may cycle on and off a few times until the heaters get hot.   It takes the heaters more than a few seconds to get hot enough to warm the cathode sufficiently to begin emitting electrons, completing the...

Anything around 24 gauge or bigger should work fine for the source and drain. Smaller stuff would be ok for the gate.

R3 and R9 will be soldered very close to the MOSFET gates?   Looking good.

While the IRF510 output MOSFET here has internal protection devices built in, it could be possible for the drain to remain "hot" even if the device failed, and the entire circuit were inoperable. A problem with the power supply, be it a Cisco or alternate DIY variety, could pose lethal to even...

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Quote: It should be fixed, but likely not the problem.    In post #5970, you have an attachment with some of your operating points. You show 46volts at the gate of Q2, but 15.4volts on the other side of R9? With a good mosfet, you should read the same voltage on both sides of R9. If...