So in this post: Figuring out a substitute for an old amp capacitor - value and type
I figured out the capacitor I had in my amp.

It was a
Red, red, yellow, black = 2 2 0 000 pf +/- 20% resin dipped polyester (Mullard C280).

In this post: Mullard tropical fish capacitors it was said that I shouldn't look for a vintage cap. It has been also said that: "Exactly the same performance can be had from ordinary "greenie" metalized mylar caps from Mouser or any other supplier". source
So I looked in the internet and I found some stores.

Now - the problem: how do I choose which capacitor should I buy? I've found some stores on the internet and they have a selection of capacitors.

How do I find which one I need ?

  • 3
    \$\begingroup\$ You can't ask for "what should I choose" here, it's off-topic to do so, by the official rules. But: you can ask for "how do I choose, what to look for", which not only helps yourself, but might be of benefit for future readers! \$\endgroup\$ – Marcus Müller Jun 27 '17 at 10:04
  • \$\begingroup\$ Also, the "ProductCompareView" link doesn't work as you seem to think it does. \$\endgroup\$ – Marcus Müller Jun 27 '17 at 10:05
  • \$\begingroup\$ I'd pick the cheapest one that meets or exceeds the specifications of the original part and fits best in the board. \$\endgroup\$ – Finbarr Jun 27 '17 at 10:18

It's tricky because unless you find an identical replacement capacitor (its specifications - manufacturer not important) the choice depends on the circuit. If you're really lucky, the circuit isn't fussy at all. Worst case scenario is the circuit relies on obscure properties, and/or relies on inferior qualities.

A capacitor has many properties. The main one, obviously, is capacitance. Other important qualities are maximum voltage it can withstand, and capacitance variability between parts. Other things like capacitance stability over temperature etc, and then there's the non-ideal capacitor properties. In theory an ideal capacitor has zero resistance and inductance; that is, it's purely capacitance. But it's obviously not the case in the real world, and sometimes that matters.

First find a datasheet for the capacitor you wish to replace. Then compare with datasheet for possible replacements. The closer the match on all properties, the better. It's as "simple" as that.

Chances are it's not hugely fussy. I'd aim for as many of these as you can:

  • Exactly the same capacitance
  • Equal or better capacitance tolerance (eg +/- 10%)
  • Equal or higher voltage, but not too much higher
  • Equal or lower ESR (Equivalent series resistance)
  • Equal or lower ESL (Equivalent series inductance)
  • Equal or lower leakage rate
  • Equal or better temperature coefficient
  • Identical capacitor type if possible - ie resin dipped polyester - but perhaps "greenie" metalized mylar will do.

And of course, size. Make sure it fits!

If you can get hold of the circuit diagram for your amp, it might provide insight for eliminating or easing many of the above constraints.

  • \$\begingroup\$ I found the original datasheet for those capacitors. Would you suggest buying from aliexpress (I think it would be cheaper to ship)? \$\endgroup\$ – George K Jun 27 '17 at 12:24
  • \$\begingroup\$ Depends where you live but Arrow, Digikey, Farnell, RS ... they all have great choice, sometimes with shipping deals \$\endgroup\$ – CL22 Jun 27 '17 at 15:06

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