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I'm replacing the capacitors in a very old tape recorder (1957) and I'm ok with the electrolytics but there are 4 with values 0.001 (x2), 0.002 and 0.005 uF i.e. 1, 2 and 5 nF. Two are marked as 250v and two as 750v. Can anyone suggest what to replace them with please?

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    \$\begingroup\$ Why do you want to replace them? What technologie are they? \$\endgroup\$ – Botnic Oct 27 '20 at 14:14
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    \$\begingroup\$ Generally you want to replace them with new capacitors of the same type. Ceramic disc for ceramic disc, polystyrene for polystyrene, etc. \$\endgroup\$ – jwh20 Oct 27 '20 at 14:26
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    \$\begingroup\$ 2 and 5 nF is non-standard. I would not heasitate to substitute 2.2 and 4.7 nF with same or higher voltage rating. Please do check for and X1, X2, Y1 or Y2 markings as well for your own and others safety. \$\endgroup\$ – winny Oct 27 '20 at 14:36
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    \$\begingroup\$ Unless in a tuned circuit, the exact value likely isn't critical. If through testing it is found to be critical, a closer value can be achieved through series/parallel combination. \$\endgroup\$ – rdtsc Oct 27 '20 at 14:59
  • \$\begingroup\$ Thanks for those comments. I'm not sure what type they are but made by ERO and axial, about an inch long. I have looked online for suitable replacements but it is hard to find something with voltage ratings so high - most seem to be rated at 50 or 100v only. I have a picture but can't see how to send pictures on here. \$\endgroup\$ – Mike Collier Oct 27 '20 at 15:11
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They are film type capacitors. Likely any plastic film part (eg. polyester aka Mylar) will work (assuming the value and voltage ratings are the same - or better in the latter case).

For example, 5nF 250V for the middle one.

5nF is not a common value, so you could probably use 4.7nF or use two 10nF in series. 4.7nF is almost surely acceptable. I don't see tolerance markings on the parts, but if it's 10% then a 4.7nF 5% part is within spec.

If the parts are not (electrically) leaky and are within spec capacitance-wise there is little reason to change them. They do not have a wear-out mechanism and those ones appear to be molded.

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