11-08-2015, 09:17 PM
I found an article on the internet about making electrect transmitters to replace the carbon ones in old telephones.
An appeal in the Wanted section on the UK Vintage Radio Forum quickly turned up the PCB artwork so I got on and made one.
The design specifies some quite odd values of capacitor but I had no trouble substituting more common ones for these. I haven't got any BC639s either so used a BC337 — and found the hard way that the pin-out is different.
I also used one for T1 and a BC327 for T2. It works very well and cost well under a pound.
I'd got a duff Number 16 Transmitter so took that to bits, turned the bottom off the aluminium casting and fitted the PCB in that. It would be perfectly possible to cut this off with a hacksaw or grind it away with a power sander. The anti-gob membrane is just a piece of thin plastic.
[attachment=12744][attachment=12745][attachment=12746]
If a larger surround allowed 'round the PCB tracks it will fit inside the earlier Bakelite Handset 164. It can be held it in place by turning over the forked connector which would normally press against the back of a carbon transmitter after well insulating the ends.
[attachment=12743]
I cut a circle from some thin packing foam, which isn't dense enough to block sound, and put in the back of the mouthpiece as a spit guard and it also helps to stop it from rattling.
As well as the cost saving no original parts are removed, other than the transmitter, so the original configuration can be easily restored if subsequently desired.
— Joe
An appeal in the Wanted section on the UK Vintage Radio Forum quickly turned up the PCB artwork so I got on and made one.
The design specifies some quite odd values of capacitor but I had no trouble substituting more common ones for these. I haven't got any BC639s either so used a BC337 — and found the hard way that the pin-out is different.
I also used one for T1 and a BC327 for T2. It works very well and cost well under a pound.I'd got a duff Number 16 Transmitter so took that to bits, turned the bottom off the aluminium casting and fitted the PCB in that. It would be perfectly possible to cut this off with a hacksaw or grind it away with a power sander. The anti-gob membrane is just a piece of thin plastic.
[attachment=12744][attachment=12745][attachment=12746]
If a larger surround allowed 'round the PCB tracks it will fit inside the earlier Bakelite Handset 164. It can be held it in place by turning over the forked connector which would normally press against the back of a carbon transmitter after well insulating the ends.
[attachment=12743]
I cut a circle from some thin packing foam, which isn't dense enough to block sound, and put in the back of the mouthpiece as a spit guard and it also helps to stop it from rattling.
As well as the cost saving no original parts are removed, other than the transmitter, so the original configuration can be easily restored if subsequently desired.
— Joe
