Bird dummyload acting up

[bob85]

Years ago i bought a cheap 250w bird load off Ebay, when it arrived it measured 60ohm on a fluke 87,
its been cooked so its no good for accurate power readings but ok for other tests, it ended up in the garrage forgotten about,

i came across it the other day & decided to put it to use, i checked it again and wtf it measured 280ohms & climbing, prodded around hoping for a better connection but no joy ,

tipped it on its back & removed the clamp to extract the resistor, removed the black cone around the resistor & pulled resistor out,

there was a greenish black coating almost everywhere on the cone & the ends of the resistor but the oil was clear, i gave it a clean & measured it,
it was all over the place depending where and how hard i pressed the test leads against it,

i decided its fcked as it is so i can't hurt anything & gently polished the ends of the resistor and the cone back to shiny copper to ensure the best connection possible & measured it again, 51ohm including the test leads anywhere i make a connection on the ends,

I put it back together & tested it with rf, it measures flat on minivna & uhf & almost zero reflect with 300w+ on hf


what i learned is don't throw your faulty oil filled loads away, clean them up first, they may not be cooked at all.

 

[autotuner]

Years ago i bought a cheap 250w bird load off Ebay, when it arrived it measured 60ohm on a fluke 87,
its been cooked so its no good for accurate power readings but ok for other tests, it ended up in the garrage forgotten about,

i came across it the other day & decided to put it to use, i checked it again and wtf it measured 280ohms & climbing, prodded around hoping for a better connection but no joy ,

tipped it on its back & removed the clamp to extract the resistor, removed the black cone around the resistor & pulled resistor out,

there was a greenish black coating almost everywhere on the cone & the ends of the resistor but the oil was clear, i gave it a clean & measured it,
it was all over the place depending where and how hard i pressed the test leads against it,

i decided its fcked as it is so i can't hurt anything & gently polished the ends of the resistor and the cone back to shiny copper to ensure the best connection possible & measured it again, 51ohm including the test leads anywhere i make a connection on the ends,

I put it back together & tested it with rf, it measures flat on minivna & uhf & almost zero reflect with 300w+ on hf


what i learned is don't throw your faulty oil filled loads away, clean them up first, they may not be cooked at all.

Bob, it has always amused me how everyone trusts their Bird. In a previous job we received a lot kit from various departments, and one of them would send their RF kit to us to check. There was boxes of Birds , loads and cables, all suspect.
So the moral is, don't trust one reading from one device, it may not be what you think.

 

[Captain Kilowatt]

So the moral is, don't trust one reading from one device, it may not be what you think.

Agreed. If you only have one device it is either always right or always wrong. How do you know the difference? That is why routine checks and calibration are needed.