I've been digesting what W8JI's excellent site has to say about metering of toob amplifiers, particularly with respect to floating the negative rail. Talking about cathode-driven G-G triode[s] here. My Hunter Bandit 2000C [2x3-400Z] has no provision for metering grid current, and a superfluous meter movement for relative output. I would have to ask anyone answering my questions to grab a copy of the schematic from BAMA. According to W8JI's site, it would seem at first glance that R-8, 100milliohms from the negative supply rail to chassis ground, with the tube grids directly grounded, it would seem the voltage drop across R8 would vary as a function of grid current.yet in this amp, according to the schematic, when set to read PLATE current the meter is directly paralleled with R-8. Taking a closer look, I observe that on W8JI's metering webpage, the cathode[s] or filament[s] center tap is returned to the negative supply rail through a plate current meter shunt whereas on the bandit 2000C the filament center tap is returned to chassis ground. As such it appears the voltage drop across R-8 is the voltage drop caused by *cathode* current [Ik] even though it's labeled Ip on the schematic. Meter polarity, positive to chassis ground when measuring "Ip" would tend to support this, I think... Setting aside the obvious concerns about shielding, bypassing, feedback loops, etc, for the sake of conversation, is it accurate to say that moving the filament center tap from chassis ground to negative supply rail would cause the meter to read Ig instead of Ik? Taking it a step farther is it also accurate to say that interpolating another 100milliohm 1% resistor between negative supply rail and filament center tap would allow the second meter [assuming both movements are the same full scale sensitivity and same internal resistance] would give a proper place to measure Ip? Thanks in advance 73, Brian KA9EGW
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