[russell_w_b]

Can you now reconnect the handset with the carbon mic insert in place, wires correct as you now have in post #43 and measure the on and off-hook resistance round the loop from terminal T8 on the telephone terminal block to terminal T1 on the telephone terminal block?

On-hook should be open-cct.

Off-hook should be about 84 Ohms with your particular carbon mic insert fitted. Again, you'll maybe need to squeeze the hook-switch contacts gently together.

Can you do this resistance measurement with the carbon mic insert removed as well? We're looking at open-circuit here.