Help with capacitors

[tonyboyle]

I have a 1960's Siebe Gorman Mk9 divers telephone with an amplifier unit inside. I am hoping to replace the old capacitors. I have a circuit diagram but need some help identifying the polarity of the old capacitors so that I put the replacements in the right way around.
I am assuming on the attached circuit diagram the symbols for a polarised capacitor is a black rectangle and a white rectangle the white side being positive?
So for example in the attached circuit diagram the positive side of C2 is connected to C1/R1. In the second photo attachment C2 has no polarity markings but I'm assuming the right end with indented ring in this photo (attached to C1/R1) is the positive end?
C1 appears to be non polar in the diagram so it won't matter which way around it goes? (Although it does have a red and black ring at the ends).
C3 and C4 are giving me trouble.
In the circuit diagram the positive terminal of both C3 and C4 is on the positive side and connected directly to R8. The negative of C3 towards Transistor 1, and of C4 towards R5.
However in the actual circuit C4 at least appears to be the other way around. The + (and indent) on C4 is linked to R5 with the blue wire which according to the diagram is the wrong way around - but I assume it must ahve worked? C3 has no indications of polarity at all so may be correct?
So when replacing C3 and C4 would I be correct attaching the positive lead to the terminals on the right connected by the black wire?
Thanks for any help!

[GMB]

I would say that C4 does not look original, so someone has replaced it and wired it the wrong way round. An easy mistake to make if they did not realise that it was using PNP transistors so the earth line in black is actually the positive supply

Non-electrolytic capacitors are sometimes marked in a similar manner - but what they are marking on cylindical foil capacitors is which end is the outermost part, so should be the earthy connection (whatever the polarity) for best screening effect.

[tonyboyle]

Thank you. So assuming C4 is wired in incorrectly all replacements thould have their positive terminal to the right (C3 and C4 connected to the black wire)?

I'm struggling to find a 0.05µF axial electrolytic capacitor for C1 - is a ceramic replacement ok at a higher voltage rating?

[Radio Wrangler]

C2 on the diagram is shown positive to the left, negative to the base of TR1 This is how it should be, R3 and R2 provide some negative bias to that base while T1 and VR1 keep the positive end of C2 at ground as far as DC bias is concerned.

C3 is a simple emitter decoupling capacitor, and the emitter is biased a little way negative due to the negative bias on TR1 base. So the negative end goes to the emitter, the positive end goes to chassis.

C4 is a simple power supply decoupler acting as a noise filter with R5 and preventing any unwanted feedback and instability. Negative end upwards on the diagram towards R5. Positive end to chassis.

David

[DMcMahon]

Originally Posted by tonyboyle

I'm struggling to find a 0.05µF axial electrolytic capacitor for C1 - is a ceramic replacement ok at a higher voltage rating?

It is not shown as an electrolytic. Ceramic would be fine, higher voltage is fine. A more modern equivalent value would be 0.047uF/47nF

David

[paulsherwin]

A 0.05uF cap is *extremely* unlikely to be electrolytic. As said, a modern 0.047uF plastic film cap will be fine. There's no polarity.

[tonyboyle]

Thanks everyone, all useful answers!

[dazzlevision]

Originally Posted by paulsherwin

A 0.05uF cap is *extremely* unlikely to be electrolytic. As said, a modern 0.047uF plastic film cap will be fine. There's no polarity.

C1 is a metal cased paper dielectric type - made by TCC.