Voltage on long tail phase inverter

[sbirkenstock]

Hi!
I just built my first guitar amp, pretty close to a Vibroverb.
It just works fine, but checking on the voltages I recognized that the voltage on the 12at7 phase inverter is 72 volts on the grid.
Plate is 270 and Cathode is 112.
Grid and Cathode seem to be way too far apart.

So I checked on a BF Vibrolux, and there is the same thing.
The voltages are:
Plate 175
Grid 50
Cathode 80

It seems when I touch the grid with my Fluke Multimeter, that the voltage is going down and stops at 72.
Can somebody give me some info on that?

Cheers,

Stephan

[martin manning]

Your meter is providing a new ground reference for the grid. Measure at the bottom of the bias resistor to get a better idea of grid voltage.

[jjman]

Look at a schematic of any Fender BF/SF with a LTPI and you'll see the voltage is measured at the point mentioned and never on those grids directly.