Testing out my new ESR meter MESR100v2 on a a PAS3 Dynamo AMP - Page 1
Forum section: electronics / testgear

author: jcrubin
author_rank: Frequent Contributor
timestamp: August 11, 2015, 01:42:37 am
content: Good evening,My MESR100v2 arrived today and I thought I would test it out with my modified PAS3 amplifier scheduled for major upgrades. The ol amp hums like a hornets nest and still runs the original selenium rectifier. Id like to ask a few questions however that I was left with after testing.As I cannot pull up a data sheet on Blackcat caps, or have been unsuccessful doing soI thought Id post some values here and see if folks could make sense of this. Note , all of this including the rectifier is being replaced anyway, I'm not looking for repair help and am migrating to the kit in this linkhttp://www.tubenirvana.net/pas3-main.htmlA modern cap would obviously have an online data sheet from which the correct ESR at a given freq would be knownThis is what I haveElectrolytic can cap (I can't make heads or tails of these values but nothing off the deep end)Value Voltage ESR Ohms30mfd 450 .94820mfd 450 2.2820mfd 450 1.1610mfd 450 1.24Black Cats (similar caps seem to have the same ESR, nothing found way off between same value caps)Value Voltage ESR Ohms Model num.05mfd 400 29.6 PKM 4S5.05mfd 400 30.2 PKM 4S5.01mfd 200 14.7 PJ 2P1.01mfd 200 15.2 PJ 2P1.01mfd 200 14.7 PJ 2P1.01mfd 200 14.6 PJ 2P1Here is where it gets interesting, not that I stopped writing down the model numbers as I couldn't find datasheetBlack CatsValue Voltage ESR Ohms Model num.02mfd 400 90.5 PRM 4S2.02mfd 400 88.8 PRM 4S2.0075mfd 400 0.784 PKM 4D75.0075mfd 400 OPEN!!!! PKM 4D75.0075mfd 400 OPEN!!!! PKM 4D75.0075mfd 400 8.9 PKM 4D75 Looks way off from the other one I can get a reading on.004mfd 400 OPEN!!!! PKM 4D4.004mfd 400 OPEN!!!! PKM 4D4Can anyone provide some feedback on the testing results....Jordan

author: dacman
author_rank: Frequent Contributor
timestamp: August 11, 2015, 02:39:00 am
content: BY mfd I suppose you mean micro-Farad (or uF). (mF = milli-Farad.) Your numbers look OK. Measurable values for the 0.0075mfd values are most likely due to parallel resistance. ESR meters work by driving Xc to a negligible value and they return the magnitude of the impedance (not Rs). Xc is not negligible at lower capacitance values, which is the reason some are reading open. Your meter appears to have a 99 Ohm full scale.

author: singapol
author_rank: Frequent Contributor
timestamp: August 11, 2015, 04:01:22 am
content: Quote from: jcrubin on August 11, 2015, 01:42:37 amQuoteI have the same model and it's VERY useful as it can read miliohms.From my experience a 10uf will read under 1 ohm standalone...typically better than 0.5 ohm.(Depends on whether 105 degree C or 85C ones...105s will be lower) as exampled by 30uf.They probably work in an audio amp but pose problem if it's s swtichmode power supply.QuoteFor small capacitances like these, I would accept them as "good"Although I find the 0.01uf untypically low.Could it be in parallel with some component? BTW did you zero the clips to minus the resistanceof the probe leads?QuoteAgain these are small value capacitances, and the meter can only read maximum of 100 ohms, so the "open"ones are actually "out of range". MESR100V2 is really a cheap and useful esr meter in terms of price and performance,I highly recommend it for troubleshooting capacitors although I caution what you measure and deduceof the condition of the cap and circuit may not be true as you are measuring in-circuit so ultimately you may need to desolder out of circuit to double check.You should also check with a capoacitance meter just for sanity. As an aside tube equipment are the way to go if you like music.This amp hums bcause I think the main power filter cap has dried up by now and low capacitance?

author: oldway
author_rank: Super Contributor
timestamp: August 11, 2015, 09:04:50 am
content: Measuring the value of the ESR has practically no interest for applications where the ripple current is of low frequency (100 Hz or 120).For these applications, it is the value of the capacity which is most important, not that of the ESR.Concerning the tube preamplifiers, the first thing to check is the frequency of the hum ... 60 or 120 hz?You must also check the value of the power supply ripple with multimeter in AC range.In the case of 120 Hz hum, it is a bad filter problem in the power supply. (capacitor who loosed his capacity)In the case of 60 Hz hum, it's probably a defective tube. (Short Circuit heater / cathode)It can also be a defective selenium rectifier (only half wave instead of full wave)NB: currently, using tubes in preamplifiers is nonsense: there are too much drawbacks: microphony, hum (heater voltage should be DC and not AC for low hum), limited lifetime of tubes, high losses, ...and no advantage at all.