[Amps] Measuring fil V

[Ron W4BIN]

    Randall, Randy wrote:

> Possible stupid question alert.  Why not measure filament current instead of voltage?
> Then you do not have to worry about accounting for losses in the filament path or the
> position of the voltmeter connection?  Or is there too much variability in the current
> drawn from tube to tube to be useable?

   As a retired broadcast engineer I can tell you:  Some equipment 
manufacturers
provide a high current shunt (100. Amperes or so for something like 62. 
Amperes)
and a dedicated Ammeter for the monitoring the filament current of the 
final power
amplifier tube.  When a new tube is installed the filament Voltage is 
adjusted to the
final factory test value and that dc current is logged and that current 
is maintained
through out the life of that tube.  (dc current for lower noise)
Such power supplies frequently feature two 24." long nichrome rods with 
an adjustable
short between them as the filament Voltage and current adjustment.

-- 
    Ron  W4BIN - Understanding is much better than
                                       knowing how.MX