Need some help with electrolytic capacitors

Question

I am restoring an old 1960s Sanyo reel to reel tape recorder, replacing most bad electrolytic capacitors.

On the preamplifier there are ten Rubycon 6.3V 4.7uF electrolytic capacitors. I assume it is old school markings. Most are are testing around 6 to 8uf. That's probably OK except the ESR of 3 to 4 ohms is probably too high.

The problem is that I cannot find 6.3V
replacements. I searched every where. The closest I can find is 50 or 63V 4.7uf capacitors. Will this be OK to use or should I go for 10uF 16V Nichicon Gold hi-end audio capacitors?

Tolerance values are high, I think around 20% or so on these old capacitors back in the 1960s.

Answer 1

There's no harm in using capacitors with a higher voltage rating than the original ones. That rating tells you the maximum voltage that the device can tolerate, and doesn't influence the two most important specifications which concern you here, capacitance and ESR.

Higher voltage ratings generally imply larger physical size, which might be of concern to you, but since modern capacitors are typically far smaller than old devices, for similar specs, I think it's unlikely to be a problem.

Answer 2

Bypass capacitors need to be rated higher than the voltage rail they are used in. So if you know that a capacitor voltage rating is higher than the previous cap it's fine to use.

But another thing you need to consider is series resistance (ESR) and that needs to be lower than or equal to the capacitor that previously was in place. ESR limits the capacitor from shorting high frequency currents, too high and the rail might get noisy.