6v6 2204 PI problems

[menger66]

The PI in my 6v6 plexi is'nt working properly, cathiodes are reading 25v WAY low grids pins 2 & 7 16v plates are around 200v, it's grounded, i've switch known good 12ax7, i measure resistance from front of 470 ohm to ground reads about 10470ohms so im stumped, im pretty sure i followed layout correctly, bad socket maybe, not making contact with pins 3 & 8? mark

[Stevem]

The cathode should read 14,470 to ground.
You have the 1 meg grid resistor?

[Ken Moon]

Defective (shorted) .1uF cap connected to PI tube pin 7?

[menger66]

yes it reads very close to 10470ohm and im using 1meg. I'll try the new coupling cap ken moon thanks for replys mark

[Bob S]

Yup that's 10k + 470 ohms.

[sluckey]

The PI in my 6v6 plexi is'nt working properly, cathiodes are reading 25v WAY low grids pins 2 & 7 16v plates are around 200v,

You cannot accurately measure the grid voltage on that type PI. The grid impedance is verrry high due to the bootstrap bias. Even a 10MΩ input impedance meter such as a Fluke 87V will load the grid voltage down to an unbelievable number. The grid voltage in a properly working LTP PI will be the same as the voltage measured at the bottom side of the grid resistors. And you can accurately measure that voltage.

Alternately, just measure the grid voltage with respect to the cathode voltage. Positive probe on the grid, negative probe on the cathode. It should be slightly negative. [/quote]