Measuring the high voltage plate Voltage

[KA5ROW]

Measuring the high voltage plate on RF amplifiers.

How can you measure the plate voltage on a amplifier?

I looked at some HV probes that can be used with multimeters, but there seems to be a problem with them handling the current. So what to do to accomplish this.

This is what I have looked at.

FLUKE 80K-6 HIGH VOLTAGE PROBE for MULTI-METER METERS!

http://www.tequipment.net/Fluke80K-6.html

[AI3V]

That probe will work.

Keep in mind it will only be accurate with a meter that has a 10MΩ input impedance.

Rege

[K1ZJH]

Probably work with the correct meter...

But note that is safety rated for use on devices with HV
supplies that are designed to deliver very low currents.

Pete

[W1VT]

You might consider using a series network of resistors to scale down the voltage. The really cheap way is to use the existing bleeder resistors. Perhaps the most accurate way is to buy a lot of precision resistors and connect identical resistors in series--and then calibrate them with a lower voltage. You should measure the voltage across the resistor closest to ground. They should all heat up identically.

Zack

[WB2WIK]

If you're measuring voltage, that has nothing to do with current.

A HV meter of any kind won't draw any current to speak of.

Measuring "plate current" or other stuff from a HV supply is not related to measuring the voltage, at all.

As W1VT pointed out, any DC voltmeter can become a high voltage meter with enough resistance in series with it. Just be careful -- a lot. It's best to connect the test instrument(s) to a HV source while that is still shut OFF, then turn on the source while you, your fingers and all body parts are nowhere near the high voltage.

[K8ERV]

Also be aware that some resistors-mostly carbon I think- change their value with high voltages. Don't know why.

TOM K8ERV Montrose Colo

[AG3Y]

Use a high voltage probe that is designed for your meter. Nothing else. I cannot believe that you guys are advocating a string of resistors. What if the guy touched a bare wire lead on one of the resistors closer to the plate cap?

Once you are dead, there is no turning back !

[WB2WIK]

Use a high voltage probe that is designed for your meter. Nothing else. I cannot believe that you guys are advocating a string of resistors. What if the guy touched a bare wire lead on one of the resistors closer to the plate cap?

Once you are dead, there is no turning back !

A HV probe usually is just a string of resistors (or possibly one very long HV resistor) with a plastic cover over it. I've built HV probes before. Mount all the resistors on a PCB then coat that with a conformal coating, then a layer of epoxy, and stick it in a PVC tube with end caps. It works, although simply buying one is probably cheaper.

[AI3V]

There are similar divider probes from many manufacturers.

Typically they have a long glass/metal film precision HV resistor inside.

A resistor, as in one .

Each manufacturer picks a resistance value so that one of the existing meter scales are accurate.

I have a Triplett probe here (paid a whopping $3), I built a simple meter that consists of a microammeter and 3 switchable range resistors, gives me a choice of 15, 30, and 60KV fullscale readings. I built in when I was repairing CRT TV's and needed to be able to measure the 2nd anode voltage.

A minutes work with Mr Ohm's law and you can work up a calibration chart to use just about any probe with any meter.

Nice thing about the commercial units is the fancy insulated handle with leakage rings- reminds you to be careful.

Electrostatic air cleaners like the ones installed in many furnace/air conditioning units have similar resistors that can be salvaged and made into HV probes.

Rege

[K8ERV]

Use a high voltage probe that is designed for your meter. Nothing else. I cannot believe that you guys are advocating a string of resistors. What if the guy touched a bare wire lead on one of the resistors closer to the plate cap?

He would become a fast learner?

TOM K8ERV Montrose Colo