• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

help converting conrad johnson MV-55 into triode!

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In UL, the screen grids are connected to taps on the O/P trafos. Disconnect the leads connecting the screen grids to the trafos at the tube sockets. THOROUGHLY insulate the ends of the disconnected leads and tuck them away neatly. Connect the screen grids to the plates at the sockets via 5 W. 100 Ohm resistors.
 
I have one on the bench for repair, so I've taken a picture.
In the picture you can see the output transformer wires connect to the PCB.
The blue wire is the anode (plate)
The green wire is the screen (G2)
There is a link that should be easy to pull out and re-plug, but on this one it's been soldered in. If yours is soldered, I'd recommend just cutting it, else the PCB might get damaged.
What you have got to aim at, is to make the link horizontal, thus isolating the green wire that goes to the primary tap, and connecting together the anode and screen grid.
There are 4 to do, each near the PCB corners.
 

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