GEC BC506 Non electrolytic capacitor question

[Mike Watterson]

No-one uses bipolar unless they need to, because they are bulky and more expensive, and less reliable.

It's decoupling the AGC. Fed from positive detector via 8.2k Ohms. One side has emitter voltage of -0.68V or more or maybe zero depending on signal level. It feeds the PXA101 base on the AGC side via IFT, so base can be -0.8V. But as signal rises the base voltage drops.

The temperature co-efficient and voltage rating won't matter on a miniature ceramic.

The 8 uF seems large. I'd try a 1uF ceramic, which is a shorter time constant. Or maybe 2uF, though the 8.2K feedback resistor is small.

If using a polarised electrolytic, then the negative goes to IFT and positive to emitter. But it's likely to go leaky on strong signals. A strange place to put the "earthy" end of AGC response time / filter cap. But I wouldn't use a polarised cap. They have a polarised 8 uF on the volume control, so it's a deliberate decision.

R&TVS 1962-1963 pages 170 - 171

I have the earlier BC505.

Edit:
Note C18 8uF polarity and voltages are with NO signal.