Though I've never owned one, I've seen a few homebrews of vintage that have a voltmeter in the front panel (some early factory sets as well). Where exactly is the meter placed - across the A supply after the rheo? - off the tube filament?... detector or amp? I'd like to incorporate one in a planned project but I'm unsure where to put it (and why).

To clear up my question a bit - should I be more concerned about voltage on the detector..... or on the amp section??? The few metered homebrews I've seen had only 1 meter and no obvious selector switch (although I'm sure some variations exist - a few even had meters to measure plate current). I want to keep it simple - only a volt meter.... but I want it authentic......

In a commercial receiver, such as an RCA Radiola 25, the meter is installed after a master rheostat called "Battery Setting" The other rheostat appropriately called the volume. Such a receiver uses '99's which have a narrow operating limits of 3.3 volts. Early '99's are said to have an operating voltage of 3-volts. The Battery Setting rheostat would be advanced as the batteries wore down. Thus, the volume rheostat would most likely be set at the same location during normal listening.

So, if a power supply were in use the changes needed to to the Battery Setting would be unnecessary...

Depending how the filament circuits are wired and what tubes are in need of careful filament voltage would determine where the meter should monitor the filament voltage.

YMMV

Chas