• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Ammeter wiring?

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I want to put an ammeter in my HV power supply, but am completly new to the concept of ammeters.

my power supply is adjustable from 150vdc-450vdc, and will have a maximum draw of 150-200 ma.

I have a Vellman 500ma panel meter that I got for like $5. Can I use this in a HV circuit? Does the shunt resistor have to be very high and if so would it cause any problems with heat dissipation?
Make sure the meter is on the negative line of the high voltage supply not on the positive side.

You can use the vellamen gauge and the type of resistors shouldn't really matter.

Just find the current draw full scale for the meter and find the corresponding resistor value.

Are you going to use a .1 ohm shunt or a 1 ohm shunt, this will decide what the size of the multiplier resistor is.

Hope this helps,

If the meters resistance is .5 ohms then it probably has a built in shunt.

You can test is with a power supply and a resistor and the meter put in the circuit and see what you get.

But I'm guessing it has a built in shunt. Most of the amp meters I have working with do.

I'm confused? If it is in series with the plate supply, how can it arc to ground?

I basically want to put it in line with the B+ output ... it would go between the B+ output and the + lead of the output transformer to measure plate current. I would put it in the cathodes but this wouldn't do me any good as I want to be able to monitor my entire power supply's current draw to keep it within the transformers ratings, and to see if there are any problems in the circuit causing excessive current draw.
Case is made of oak...and any panels are made of PVC. Yeah I know, maybe a fire hazard but I have a main kill switch nearby and a fire extenguisher handy at all times. Its very well built and shielded inside as well.

I guess I could put it in the negative rail...will the .5 ohm resistance mess anything up with the ground potential? I wouldn't think so but just asking...
Here is an example from Yamamoto:



Go here for more details...


-- josé k.
thanks for the reply, but those show the meter in the cathode. This is great information on measuring bias for when I built my power amp prototyping box, but right now what I want is a master current meter for the entire B+ line so I can see what draw my amps are pulling when operating so that I can have the right size transformers made for my guitar amps.
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