Hi guys! I've recently come into possession of a GPO 332 telephone, and have attempted to convert it to work on a modern system. It should be noted that the telephone was in less than ideal state when I received it, missing the cable used to connect it to the phone line, and having been kept in a loft for some time.
Using the information available
here and the wiring diagram available
here I removed the relevant straps, installed a 3.3kΩ resistor & a 205 rectifier, and double checked the handset was wired correctly (it appears to be).
The telephone dials out fine and can receive calls, with a beautifully loud ring might I add!
However, the receiver's volume is so low I initially thought it wasn't working at all and spent a solid 90 minutes pouring over the wiring to make sure I hadn't made a mistake somewhere. I discovered that making tones by pressing buttons on my mobile were getting through, but barely. I can hear the pulses when dialling just as clear as I can on my GPO 746, but the dial tone is so inaudible it may as well not be there, outside of when I press down on the hook and I can hear it for a half second or so. I've spent a good 4 hours trying to get this telephone working and I'm ready to accept defeat and ask you wonderful people for help. I've attached images of my (temporary, I promise!) wiring below. I've also tried wiring up my 746's handset but got the exact same problem, but it could simply be the handsets are not interchangeable. In case it helps, the telephone has a Receiver Inset No 1L installed. I'm a complete layman when it comes to vintage telephones so please excuse any incorrect terminology or faux pas I may have made.
To summarise:
Call audio is quiet almost to the point of not existing, no sound appears to be transmitted either.
The telephone dials out & receives calls fine.
Pulses can be heard clearly when dialling out.
Dial tone becomes audible for a moment when hook is pressed down.
(Somewhat unrelated: Could anyone tell me what the pictured rubber gasket is? It fell out while I was disassembling the telephone to take pictures and I've no idea where it came from, thank you)