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Accurate Low Amp Current Probe Advice

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KungFuJosh:
I assume the lower ESR & higher ripple handling of my newer caps helped filtering. Here's what mine were, all tested out of circuit on IM3570:

50V 2200uF    Old: 60mΩ ESR    New: 13mΩ ESR
50V 1000uF    Old: 120mΩ ESR    New: 11mΩ ESR

Thanks,
Josh

Martin72:

--- Quote ---I assume the lower ESR & higher ripple handling of my newer caps helped filtering.
--- End quote ---

This would make sense for a switched voltage, but I cannot imagine that an auxiliary voltage is generated in a switched manner on the AM503B board.

MarkL:

--- Quote from: KungFuJosh on November 20, 2024, 07:21:07 pm ---I assume the lower ESR & higher ripple handling of my newer caps helped filtering. Here's what mine were, all tested out of circuit on IM3570:

50V 2200uF    Old: 60mΩ ESR    New: 13mΩ ESR
50V 1000uF    Old: 120mΩ ESR    New: 11mΩ ESR

Thanks,
Josh

--- End quote ---
Yes, no doubt replacing those caps improved the ripple.

However, if the designers did their job, the worst case characteristics of the capacitors (including initial -20% of C, temperature effects, and end-of-life DF) would be taken into account.  The next stage of linear regulation would continue to reject enough ripple to meet a unit's specifications, or if no warranted noise specification exists as is the case here, to at least meet nominal characteristics.  Sure, that's putting faith in the designers, but I think it's a good bet from this era of Tektronix.

What was the capacitance of your old capacitors (@120Hz)?

nctnico:

--- Quote from: Martin72 on November 20, 2024, 09:47:59 pm ---
--- Quote ---I assume the lower ESR & higher ripple handling of my newer caps helped filtering.
--- End quote ---

This would make sense for a switched voltage, but I cannot imagine that an auxiliary voltage is generated in a switched manner on the AM503B board.

--- End quote ---
Yes. The 1000uf / 2200uf capacitors are all used for mains ripple filtering which means a frequency of 120Hz at most. At this frequency regulators and opamps have a very high attenuation. I don't think you can even measure the difference in ripple with new versus old capacitors. The series resistance of wiring, PCB traces, rectifier diodes and transformer windings is likely higher compared to the ESR of the original capacitors. Maybe the 1uf bipolar capacitor can make a difference; I have not checked where this is at in the schematics.

KungFuJosh:

--- Quote from: MarkL on November 20, 2024, 10:20:11 pm ---Yes, no doubt replacing those caps improved the ripple.

However, if the designers did their job, the worst case characteristics of the capacitors (including initial -20% of C, temperature effects, and end-of-life DF) would be taken into account.  The next stage of linear regulation would continue to reject enough ripple to meet a unit's specifications, or if no warranted noise specification exists as is the case here, to at least meet nominal characteristics.  Sure, that's putting faith in the designers, but I think it's a good bet from this era of Tektronix.

What was the capacitance of your old capacitors (@120Hz)?

--- End quote ---

I don't recall the cap values being out of spec enough to take note of it, however, I was mostly focused on ESR.

I don't doubt the skills of the designers being far greater than mine; but I do know the tech we have now, along with what caps available, are much better than what was around 30 or 40 years ago.

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