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Was checking voltage drop across the power supply choke and a resistor. Only one tube in circuit and I am checking at 1st choke and at cathode 10 ohms to ground.
The choke ma reading is higher at 32ma and cathode 10 ohm resistor is 27 ma. My understanding is in a series circuit the current is same. I measured the choke resistance, it is 407 ohms.
This is interstage transformer and fixed bias circuit if that makes a difference.
Thanks Tom
Follow Ups:
Well put a few amp meters in two spots and got these results. Before the 1st choke 30.9 ma after last cap 29.9. Also did voltage drop accross 1st choke and this time was close to the 30.9. Also the 10 ohm resistor at the cathode was 29.8 so very close to the last cap in power supply.
The good news is the 10 ohm test point is on the money. You guys where right about AC ripple causing some issues even with the amp meters. Also my fluke 87 meter has a blown fuse. Got a new one on the way.
Thanks guys for the help you nailed this one!!!
Tom
Don't forget to take into account the internal impedance of the measuring device.
When measuring voltage drop across two circuit nodes the meter impedance is very high.
But when the meter is used in current mode its impedance is very low.
The only meaningful measurement of voltage and/or current by a meter is across a resistor.
Omnes feriunt, ultima necat.
You might want to insert a current meter.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hey Tre
I have a few meters I can use but I am confuse why the different readings. The ten ohm resistor is a actual test point I can get to with everything sealed up.
Will see if meters show same reading in both spots at the choke and resistor. If they are I might be losing current somehow.
Thanks Tom
Measuring voltage across a resistance and then calculating relies on the accuracy of the resistance reading. If you insert your multimeter (in the current mode) into the circuit at each spot and that reads different, then they are different for sure.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Voltage across a power supply choke likely includes AC as well as DC components.
"Voltage across a power supply choke likely includes AC as well as DC components. "
And the AC component is likely not sinusoidal. This is not a good place to measure current. It would be better to insert a current meter like Tre suggested, probably after the last filter cap.
--------------------------
Buy Chinese. Bury freedom.
The choke resistance will increase when hot - so it will read higher as it warms up. In fact this characteristic is used to measure internal temperature in transformers and choke / motor windings.
Edits: 12/27/21
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