Can anyone suggest a practical use for this gauge on a tube amp

[devilsindetails]

Big fan of the look of old electronic volt/amp etc. gauges. Came across this one recently and wondered if it might be useful to implement with one of my tube amps.

Range seems to be 0-100 D.C. (i am assuming volts) dial face shows res. 270 ohms and F.S.D. = 1 mA.

What does. F.S.D. designate?
Any ideas of what I might be able to use this for.?
What would the third connection at the noon position be for?

(Mods feel free to move this to a more appropriate section if necessary)

 

[fpitas]

F.S.D. most likely means full scale deflection.

 

[nigelwright7557]

You could put it across B+ if you use resistors to scale the voltage.

1mA FSD means it needs 1mA to measure 100VDC on the gauge.

Its likely the meter has resistors already inside it so they would need to be changed to read other voltages.

 

[Mooly]

If it is 270ohm internal resistance and 1ma F.S.D. then it needs only around 0.27 volts to swing it fully over. Try it on a 1.5v battery with a 1.5k series resistor.

You could make an ammeter with a shunt resistor across the terminals or a voltmeter by adding a series resistor to suit the range.

The middle terminal could just be a ground to earth the casework and internals for safety.

 

[devilsindetails]

You could put it across B+ if you use resistors to scale the voltage.

1mA FSD means it needs 1mA to measure 100VDC on the gauge.

Its likely the meter has resistors already inside it so they would need to be changed to read other voltages.

If it is 270ohm internal resistance and 1ma F.S.D. then it needs only around 0.27 volts to swing it fully over. Try it on a 1.5v battery with a 1.5k series resistor.

You could make an ammeter with a shunt resistor across the terminals or a voltmeter by adding a series resistor to suit the range.

The middle terminal could just be a ground to earth the casework and internals for safety.

Thanks gents...time to do some 'xperimentin'

 

[indianajo]

Yeah, I ran B+ out to an unused terminal of the "preamp power" socket of my ST70. B+ sags so fast, average life of a main cap (sprague or CDE cans from the seventies) was 8 years. The average life of a 5AR4 (GE or RCA from the seventies) was 10 years. This was 4 hours a night and 12-30 hours on weekends.
Idle current on the output tubes was also an interesting measurement, but I found it went to **** slower than the B+. Output tubes lasted about 12 years, so when I put the new can B+ cap in, the idle current would go back to near where it was supposed to be. Of course ST70 idle current was affected by the ****y selenium rectifier on the bias voltage, which had a short life of its own (bad about 1974 when the amp was 13 years old).