Plan 7
 

I've got at bell set 44 with a 248 hooked up to a 328. The whole thing is then connected to a extn on my exchange. It's all been working fine for a couple of years now but one thing I've never been able to solve is that when the set is connected direct, bell set to extn, the receiver is very quiet on the bellset handset. The extn handset is fine. It's odd as when you dial in from outside the volume is fine, on both the bellset phone and the extn. I've cleaned up all the contacts on the switching mechanism and the relay that shows the extn. is busy but to no avail.

I think this is something to do with the low resistance between the phones when they are directly connected as there is no proper "balance" on the line but I don't really know what to look for.

One other clue is that if I don't touch the setup for a two or three months the volume drops to a very low level, to the point where it doesn't sound like it's working at all, but then picks up to the usual quiet level when i re-clean the contacts. So maybe it's a dodgy connection.

Any ideas?

Re: Plan 7
 

If I undersand your description correctly, the problem is confined to the "Speak to extension" setting. If so, then it has to be that something (e.g. oxidation in a set of contacts) specific to the contacts in use in that position is attenuating the signal. Could you try working your way through that signal path (with the setup NOT powered up - either by line or local battery) measuring the resistance across various points, to localise the problem?