EL34 Socket Wiring for Bias Metering

[ViperDoc]

I'm building a 2 x EL34 Marshall. Is it necessary to wire pins 1 to a separate ground for keeping pins 8 isolated for measuring cathode current, or can you tie pins 1 and 8 together to the 1R resistors to ground?

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[sluckey]

Either way is fine. It's your choice. I would strap pins 1 and 8 together just for simplicity.

[harleytech]

Either way is fine. It's your choice. I would strap pins 1 and 8 together just for simplicity.

That's the way I do it !

[mhuss]

+1 -- the suppressor grid ( pin 8 ) current is negligible, so it won't affect your reading, and it is simpler to wire them together.

[pdf64]

I like to wire the current sensing resistor between terminals 1 & 8, then run the 0V common wiring on up and down the chain from those points

[ViperDoc]

Much appreciated!

[TUBEDUDE]

I wire pin 1 to the raw bias supply, and pin 8 to the cathode resistor.

[pdf64]

I wire pin 1 to the raw bias supply, and pin 8 to the cathode resistor.

But that mode of operation is undocumented / unsupported by the published info, so how to work out the loadlines?
I guess one option is to plot your own!

[mhuss]

I like to wire the current sensing resistor between terminals 1 & 8, then run the 0V common wiring on up and down the chain from those points

That certainly makes sense if you're running a proper 0v line along the power tubes, but many vintage amps connect the cathodes to chassis/ground individually and locally, so socket terminal to solder lug is perhaps easier to do.

The resistor pin 1 to 8 idea is good for new builds where you can wire it early on before things get cluttered, or in old Fenders where the ground lead is physically soldered to the chassis (provided the sockets have a pin !

[TUBEDUDE]

I wire pin 1 to the raw bias supply, and pin 8 to the cathode resistor.

But that mode of operation is undocumented / unsupported by the published info, so how to work out the loadlines?
I guess one option is to plot your own!

I Ballparked the circuit using examples from Garnet and Traynor schematics as a baseline.
You could breadboard, varying the g3 voltage to chart changes, much like testing how varied screen voltages affect operation, just much smaller changes.

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