New filter capacitors vs old tolerances


My Technics su-v8 has 4 10000uf capactors but with high tolerance -20%.+80%. I removed the bludging tops to find it was only the plastic that had wrapped, i have another Technics SU-V8, but its caps are perfectly flat and it was from a diseased estate. so possible an easier life. Both built in 1980. The new capacitors for instance do they measure less? than the actual capacitance on the plastic cover? CDE 383LX 10000uf i am looking at due to the high temp and life. They stated at ± 20%. Is it possible the old capacitors measured more than indicated on the plastic slip, i assume the emitter resistors being 3watt might suggest they are not 12000 or more the old ones. The new ones would be more on the low side? it appears a common issue with the old capacitors with these high tolerance figures, going by the audio forums. The rectrifer stock diodes are 3A 400V.

Hi SamMac,

I’m not clear on what you are ultimately asking, but to cover a few things –

Yes, it is possible that the caps that were on each of your units had capacitance higher than 10,000uF, since their tolerance was +80/-20% (a range of 8,000uF to 18,000uF), but the engineers who design such things would assume the worst case of -20% for the value of those capacitors, so any 10,000uF cap rated for no worse than -20% would be acceptable. The actual value of these caps is not critical, as their purpose is just to store a reserve of charge for when the amp needs it, rather than some sort of precise value for some sort of frequency-dependent filter application.

Related to the first point, there would almost certainly be no harm in going with higher values (or higher voltages) in this application. Even if you assume you shouldn’t exceed the upper possible limit of the old caps, which isn’t necessarily the case, you could go with 15,000uF +/-20% caps and still not exceed 18,000uF (15,000uF plus 20% is 18,000uF).

I would be more concerned more about finding caps rated for long life and high temperatures that fit in the same mounting points than finding exact matches of capacitance values in your application.

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Hi @David_1528,

Thank you for your reply and help.
That is what i was asking, and that the new capacitors of today are mostly ±20%. I was looking at the 338-383LX103M080A082-ND or 12000uf, however I would expect the rectifier diodes and emitter resistors would have to be changed?

Maybe the rectifiers 3A 400v and Emitter resisotrs 3W 0.47ohm 10% tolerance can handle the 12000uf if the tolerance is high ( + 80%) as you said, or would it be a safer option to change them to 5watt and 6A diodes. Thanks Sam

Hi SamMac,

I wouldn’t expect that changing the capacitors to 12,000uF +/-20% would change the nature of the circuit in any way that would require increasing the power and current handling requirements for the emitter resistors or rectifiers.

The capacitance value should have no bearing on the emitter resistors’ requirements at all, and it’s unlikely to have a significant effect on the diodes’ requirements. And, as you say, since the maximum value of the original caps (18,000uF) is higher than your proposed 12,000uF ones, it is still within the nominal range of the original design.

On the other hand, there’s almost certainly no harm in doing so. It would merely add an additional margin of reliability, as you would be running them even further below their maximum ratings.

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Hi @David_1528

The original value on the capacitor case is 10000uf. The other amplifer was 8200 again with the +80 - 20%. An extra 2000uf would not hurt, especially with the tolerance range up to 18000uf. The new CDE 10000uf could be -20 below and also maybe +20. In audiokarma, someone said that new capacitors are a bit of the low side? if so then 12000uf would suit. Have a wonderful Christmas and New Year, Thanks Sam

12,000 uf 105C we have in stock [Aluminum Electrolytic Capacitors | Electronic Components Click here

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@Robert_1552 Thanks Robert, the size is a bit wide and high, so i am stuck with the CDE brand (which seems popular), love Nichicon in power supplies, shame the PW series is being phased out. The orignal cap height and width is 35mm x 80mm height, have a wonder Christmas and New Year, Cheers Sam