Simulating old caps with new parts

I'm working on an old 60's keyboard which needs new caps in the power supply (edit: and elsewhere). Since any change to the sound is likely not going to be well recieved, is there a simple way to model the leakage characteristics of the old caps? I guess i could measure the leakage current and parallel the cap with a resistor, but that's only the static DC condition. Is there an AC or some kind of time-based aspect to leakage etc that i don't know of?

I'm not sure that leakage would be desired in most situations.  Non-zero power supply impedance is a different story.  You can definitely hear "sag" in applications like a guitar amplifier.

For sure. Maybe leakage isn't exactly what I'm looking to model, but there *is* leakage in the old caps, i change em to new ones, and there's a noticeable difference in sound. Which is bad. Has to sound the same (but contine working lol). Guess I'm not sure what other characteristics of old caps I'm looking for? And how to fake that...

I very seriously doubt that any deficiencies in power supply caps would have any audible effect. If it's tube gear and the rectifier is a tube, tube rectifiers have high series resistance (usually 100 ohms or so) that can contribute to power supply sag (although transformer saturation equally likely to be responsible for supply sag). But you're just replacing caps so that is of no interest. The most leaky / high esr power supply filter capacitors will have zero (0) effect on sound. Electrolytic capacitors used for filtering could in theory but I personally doubt anyone could actually hear that. Certainly not in some old 60's tube gear which probably already has a bit of grit / warble to it.

So just pop in new caps that are the correct size and you're done.

Dreams said:

For sure. Maybe leakage isn't exactly what I'm looking to model, but there *is* leakage in the old caps, i change em to new ones, and there's a noticeable difference in sound.

Click to expand...

Leakage is not the cause of the change in sound. The two main causes are:
The new cap has a significantly higher capacitance than the old one, which, after the years has probably lost 3/4th of its capacitance. You (or the owner) has got used to this lower capacitance effect, but it does not reflect the performance of the amp when it rolled out of the factory.
Modern caps have much lower ESR, which results in less rounded transients. You may try adding a resistor in series with the cap, not much, a few ohms, till you are satisfied with the result.