The reference point of taking voltages in Philco20 - Printable Version

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The reference point of taking voltages in Philco20 - morzh - 11-06-2011

I guess, my question has been lost in the previous thread, so I will dedicate a separate thread to it.

My general understanding (and the lifelong practical experience) tells me that all voltages are measured relative to GND (Chassis), unless specifically noted otherwise.
Looking at the Voltage Chart in a Philco 20 manual (the link that was given to me here) I am a bit confused by what I see in there.

Example1: The Cathode voltage of the 27 tube (1st Audio stage) is shown at 8V.
The cathode is tied to the GND, so it has to be 0V.
This leaves me with two answers:
1)the measurement is done relative to some point, other than GND/Chassis
2) It's a mistake in the chart.

Example2:
The Grid voltages of three first stages (all 24 tubes) are shown at 3V/3V/1V respectively. My meter (a Fluke) shows 0V, and I think justly so, as the grids are connected to GND with coils, that present pretty much a short for DC.
Again, are those taken relative to the Chassis GND?

Also if someone can tell me what this means:

"Tube socket readings taken with AC Set Tester, AC Line, 115V".
My understanding is that all voltages are measured at 115V in the outlet.
1)What does "AC Set Tester" mean?
2)Why "tube socket?" Are the tubes themselves absent? Or are they installed?


Thanks,

Mike.

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