Caps: To replace or not to replace?

[Vakito227]

Hi all, I'm still not an expert by any definition at all but after the success of restoring my '58 HMV stereo record player I thought I would step it up a notch and buy an EKCO 9 Octave which looks to be from the same era to hopefully restore back up to a good standard. The good thing about this one is the amplifier unit can be unplugged and pulled out of the main case which makes working on it a whole lot less fiddly.

Anyway I have only given the amplifier circuit a quick inspection to weigh up what capacitors need replacing and which ones can be left be (such as polystyrene and micas). I was expecting to find polystyrene caps around the tone controls but instead I have found what look to be tiny versions of the infamous hunts capacitors. One or two appear to be cracked too but I thought I would check whether it is vital to change these caps before I start throwing money at the wall and also because these ones around the tone controls are very awkward and fiddly to work with.

I have also found a cap elsewhere in the circuit that I'm having trouble identifying. According to the circuit diagram, it has a very small value of 56pF. Any help identifying it would be appreciated.

Thanks
Peter

[MrBungle]

The last image, assuming that's the 56pF one, looks like an old fashioned silver mica that the wax has melted off.

[Herald1360]

The tiny Hunts will be leaky....... but whether this matters depends on whether they're supposed to be blocking any dc and how the circuit impedances around them might be affected by their leakage resistances. There are places where 100k or even less leakage resistance doesn't matter but they're not the norm.

[paulsherwin]

As a general rule, you don't need to worry about caps with a value less than 0.001uF.

[Vakito227]

Thanks for the advice, what I'll do is get some replcements for those small hunts capacitors just in case and if the circuit works fine without the need to replace them then I'll leave them be. Regarding that 56pF mica capacitor, I know micas rarely go bad but is it worth replacing anyway?

[Nuvistor]

If that 56pf cap is working, which it probably is, leave it in circuit.
Frank

[vidjoman]

I would change all those Hunts caps. We were changing them in the 1960's as they mostly had a short life. The Mica types rarely fail and can be left alone, as has previously been mentioned. Even the later Hunts plastic coated caps were not much better.
You have to keep in mind that they were early plastic coated caps and, at the time, were an innovation after the paper waxies. The plastic was not very well applied to them and perhaps that was part of the problem and I think it's not very temperature stable and cracks when used in valve equipment.

[Vakito227]

Fair enough, I'm finding it difficult to find a 0.002uF cap that suits my requirements so am I right in thinking I can wire 2 0.001uF caps in parallel to create the same effect?

[MrBungle]

That would indeed do the job.

[julie_m]

Unless it's part of a timing circuit, the more modern preferred value 2.2nF probably will be fine.