722 Trimphone ringer diagram - UK Vintage Radio Repair and Restoration Discussion Forum

nigelr2000 · 1st May 2015, 10:51 am

Hi all got another trimphone to play with so I wired it as my other full working one using the info from the net and have no ring, at first I realised the line cable was 2 wire so added the link between T6 & T7 (not shown in the picture), I now read about 14 volts on the ringer wires (DMM) but still nothing on the ringer. Its the 2 transistor type 8A but I can only find a diagram for a 5A. Is there a way to wire it off the phone just to test the ringer ?

I am using my telephone test rig (ex TV magazine designed one) and it has up to now worked perfectly testing phones but just in case I plugged into the main line and I was able to dial BT line test but nothing was heard on ringback bar my cordless ringing so I think I am looking at a ringer fault.

Pictures enclosed in case I have wired something wrong.

OscarFoxtrot · 1st May 2015, 12:33 pm

I don't have a circuit, but:

The tone caller, No 8A, was a novel feature of the trimphone. It consisted of an oscillator of about 2 kHz driven from rectified ringing current which gave it a vibrato effect.

The oscillator uses a tuned winding on a transformer (top left) and two transistors, which are BC108.

Earlier versions prior to the Telephone 2/722 were fitted with a slightly simpler design, tone caller No 5A, with only one transistor and which used a thermistor to provide the crescendo feature. The 8A uses a transistor fed by a capacitor with a bleed resistor. On each burst of ringing the capacitor charges up more than it discharges in the quiet period, until it is fully charged turning the transistor fully on to give maximum volume from the sounder.

http://www.samhallas.co.uk/collectio..._trimphone.htm

Ignoring the thermistor the ringing board just connects to the telephone line through a capacitor in the same was as a bell motor.

You can probably substitute a Receiver for the ringer sounder temporarily. That should localise the fault to the main tele. PCB, the ringer PCB, or the ringer sounder.

1st May 2015, 10:51 am	#1
nigelr2000 Heptode Join Date: Nov 2008 Location: North Walsham, Norfolk, UK. Posts: 900	722 Trimphone ringer diagram Hi all got another trimphone to play with so I wired it as my other full working one using the info from the net and have no ring, at first I realised the line cable was 2 wire so added the link between T6 & T7 (not shown in the picture), I now read about 14 volts on the ringer wires (DMM) but still nothing on the ringer. Its the 2 transistor type 8A but I can only find a diagram for a 5A. Is there a way to wire it off the phone just to test the ringer ? I am using my telephone test rig (ex TV magazine designed one) and it has up to now worked perfectly testing phones but just in case I plugged into the main line and I was able to dial BT line test but nothing was heard on ringback bar my cordless ringing so I think I am looking at a ringer fault. Pictures enclosed in case I have wired something wrong. Attached Thumbnails

1st May 2015, 12:33 pm	#2
OscarFoxtrot Heptode Join Date: Apr 2011 Location: Edinburgh, UK. Posts: 805	Re: 722 Trimphone ringer diagram I don't have a circuit, but: The tone caller, No 8A, was a novel feature of the trimphone. It consisted of an oscillator of about 2 kHz driven from rectified ringing current which gave it a vibrato effect. The oscillator uses a tuned winding on a transformer (top left) and two transistors, which are BC108. Earlier versions prior to the Telephone 2/722 were fitted with a slightly simpler design, tone caller No 5A, with only one transistor and which used a thermistor to provide the crescendo feature. The 8A uses a transistor fed by a capacitor with a bleed resistor. On each burst of ringing the capacitor charges up more than it discharges in the quiet period, until it is fully charged turning the transistor fully on to give maximum volume from the sounder. http://www.samhallas.co.uk/collectio..._trimphone.htm Ignoring the thermistor the ringing board just connects to the telephone line through a capacitor in the same was as a bell motor. You can probably substitute a Receiver for the ringer sounder temporarily. That should localise the fault to the main tele. PCB, the ringer PCB, or the ringer sounder.