Hi Galu.
I purchased the tester you recommended.
Bare bones but inexpensive and automatically decides what it is testing.
I cut the wires from the two caps lying on their sides to isolate them from the circuit board.
Following a number of tests here are the results.
Existing 3.5uF Cap (found to be polarity conscious)
Tested to average 5.45uF (ESR 2.5Ω, & V Loss 1.2%)
Existing 2.7uF Cap
Tested to average 3.15uF (ESR 0.51Ω, & V Loss 0.25%)
As a reference, the tester displayed 46.61uF at 0.32Ω for the 47uF Jantzen poly cap I have on hand.
To test the existing 18uF & 47uF caps I need to de solder.
I see what you mean about size when it comes to poly vs electrolytic at 47uF.
I'll have to ponder the best way of fitting these.
Maybe a separate board to hold the 2 large caps with wiring back to the existing circuit board termination points?
Now you're cooking with gas, Cliff! 
Using the poly cap as a reference has given you a good indication of what magnitude of ESR you should expect from a good capacitor.
The 3.5uF electrolytic has aged badly, as indicated by its very high capacitance and ESR readings.
As we previously discussed, there's no electrical problem with connecting a physically much larger 47uF poly capacitor 'off board', you just have to mount it and its wiring securely.
When doing a similar renovation, I was happy to replace the ancient 47uF NP electrolytic bass shunt with a new NP electrolytic. The difference this made to the quality of the bass was enormous. Prior to the renovation, the owner had been listening with his amplifier loudness control engaged.
After the renovation, he no longer had to use the loudness control, as the bass had really firmed up.
Using the poly cap as a reference has given you a good indication of what magnitude of ESR you should expect from a good capacitor.
The 3.5uF electrolytic has aged badly, as indicated by its very high capacitance and ESR readings.
As we previously discussed, there's no electrical problem with connecting a physically much larger 47uF poly capacitor 'off board', you just have to mount it and its wiring securely.
When doing a similar renovation, I was happy to replace the ancient 47uF NP electrolytic bass shunt with a new NP electrolytic. The difference this made to the quality of the bass was enormous. Prior to the renovation, the owner had been listening with his amplifier loudness control engaged.
After the renovation, he no longer had to use the loudness control, as the bass had really firmed up. 
This time I shorted the cap for 10 seconds.
New series of tests
Existing 3.5uF Cap (found no longer to be polarity conscious & averaged similar figures when swapping the poles)
Tested to average 5.65uF (ESR 0.69Ω, & V Loss 1.3%)
Would you say both caps have deteriorated?
At what values should ESR & V Loss be consider unserviceable?
New series of tests
Existing 3.5uF Cap (found no longer to be polarity conscious & averaged similar figures when swapping the poles)
Tested to average 5.65uF (ESR 0.69Ω, & V Loss 1.3%)
Would you say both caps have deteriorated?
At what values should ESR & V Loss be consider unserviceable?
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That's a complicated question because ESR depends on so many factors.
Just expect an electrolytic capacitor to have a higher ESR than a film capacitor.
A typical electrolytic in a loudspeaker crossover could have an ESR of a couple of ohms compared to the couple of tenths of an ohm of a film cap.
For loudspeaker crossovers, I submit that an ESR below 1 ohm is desirable. This I will call 'Galu's Law'!
Regarding 'V Loss', a couple of % is probably good for electrolytic caps.
Over to you, Cliff, which of the caps would you now judge to have deteriorated and why?
Just expect an electrolytic capacitor to have a higher ESR than a film capacitor.
A typical electrolytic in a loudspeaker crossover could have an ESR of a couple of ohms compared to the couple of tenths of an ohm of a film cap.
For loudspeaker crossovers, I submit that an ESR below 1 ohm is desirable. This I will call 'Galu's Law'!
Regarding 'V Loss', a couple of % is probably good for electrolytic caps.
Over to you, Cliff, which of the caps would you now judge to have deteriorated and why?
Over to you, Cliff, which of the caps would you now judge to have deteriorated and why?
Even so, I suspect their values will also be out.
2 out of 3?
- The 3.5uF Cap should be replaced because its capacitance is out by 36%
- The 2.7uF Cap will be replaced because its capacitance is out by 15%
- The 18uF and the 47uF Caps will also be replaced.
Even so, I suspect their values will also be out.
2 out of 3?
If I go for a pcb style board to mount "off board" are the "paper" types ok, or do I need FR4 rating or bakelite type?
Don't know whether caps, inductors, and resistors heat up or a fire risk??
Full marks, Cliff!
I would simply attach the large cap firmly to an offcut of plywood/mdf using plastic ties.
FR-4 is the most commonly used material in PCBs. It is a glass reinforced epoxy laminate sheet.
However, there is no need to overthink this as the components in domestic loudspeaker crossovers do not get warm enough to require any special precautions to be taken.
I should have added that, under fault conditions, ceramic resistors can become hot enough to char a pcb. That's when a heat resistant pcb is important.
However, Cliff, it is safe to say that your remotely located 47uF film capacitor neither poses a heat risk to the board on which you mount it, nor is in danger of being heated by the other crossover components.
However, Cliff, it is safe to say that your remotely located 47uF film capacitor neither poses a heat risk to the board on which you mount it, nor is in danger of being heated by the other crossover components.
Thanks.
All this information is very useful to me and is helping me build my skill level.
With the Yamaha speakers my aim is for a professional looking finish, as well as a technical improvement.
I found a source of fire resistant pcb boards for around AUD$0.80 each.
Less fiddling around, and they include a grid pattern of holes for zip ties and for solder connections.
I have a quantity of male and female non ferrous wire terminals.
I'll fit these so the "outboard" can easily be de coupled from the main crossover board should future work be required.
These will be color coded so caps don't get mismatched on the circuit board.
All this information is very useful to me and is helping me build my skill level.
With the Yamaha speakers my aim is for a professional looking finish, as well as a technical improvement.
I found a source of fire resistant pcb boards for around AUD$0.80 each.
Less fiddling around, and they include a grid pattern of holes for zip ties and for solder connections.
I have a quantity of male and female non ferrous wire terminals.
I'll fit these so the "outboard" can easily be de coupled from the main crossover board should future work be required.
These will be color coded so caps don't get mismatched on the circuit board.
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