I just rebuilt my ESR meter.
I found the schematic on the web, see ORIGINAL-schematic.png for author.
This works well and is easy and almost free to build.
It is analog (which I prefer), and uses a 50uA meter.
Resistor R13 depends on your meter and pot.
The way I chose it was to set the 10K pot to mid-range.
Then uses a resistor substitutuion box to zero the meter.
This gives you a plus-minus on the zero pot.
8K2 was the closest standard value.
On my other version it was 3K3.
Yes I have a large white cat, named Gus, he likes to play with wires and push stuff onto the floor.
You may see some fur on the pcb.
We call this "Gus sign". (as in Dune's "Worm Sign").
The meter and knob are recycled.
To use you short out the leads, and zero the meter to full scale.
Then use it as an ohm meter.
I put DC blocking caps in both leads and run it off a battery.
This is for when I work on my tube gear, I can test in-circuit.
The smaller the reading, the better the cap.
It is a good idea to have some good test caps to verify your readings.
Anyway - Enjoy.
edit: updated to parts actually used.