Why strap T5 to T6 in 700 series telephones? - UK Vintage Radio Repair and Restoration Discussion Forum

Dave Moll · 25th Jul 2020, 4:28 pm

As per the title, I have never quite understood the purpose of the strap between T5 and T6 in 700 series telephones. Without it, the gravity switch would disconnect the ringer when the handset is lifted, whereas this strap means that it remains connected across the line. Does this have an effect on the speech performance of the telephone during use, or is it simply a hangover from earlier telephones that didn't have a switch contact in this position?

dagskarlsen · 27th Jul 2020, 5:45 pm

Seen from non UK (=Norway) I see no reason for that strap, but we have capacitors in each phone. (no master socket)

dsk

Dave Moll · 27th Jul 2020, 5:55 pm

I don't think it's related to where the capacitor is located. After all, the 700 series of telephones pre-dates the introduction of master sockets with capacitors in them - and ringers were connected in series to avoid bell-tinkle when dialling.

The thing that seems strange to me is that a changeover switch was introduced with the 700s (in contrast with the simple switch in earlier 'phones to make a loop) but the chageover contact was shorted out.

OscarFoxtrot · 27th Jul 2020, 6:15 pm

The option may have been intended (whether used or not) for some plan systems where the ringer had to be rung (eg to signal an exchange call) even when the phone was in use (eg on an internal call).

russell_w_b · 27th Jul 2020, 6:35 pm

Isn't the link removed for shared service working?

russell_w_b · 27th Jul 2020, 7:18 pm

I notice that on the cheaper ASTIC-less 'Etelphone' made by Ericsson (N1900) the paster diagram shows the link between T5 and T6 is removed. Drawing N112419/4 refers.

ThePillenwerfer · 27th Jul 2020, 7:45 pm

Quote:

Originally Posted by russell_w_b

Isn't the link removed for shared service working?

Yes.

25th Jul 2020, 4:28 pm	#1
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 4,978	Why strap T5 to T6 in 700 series telephones? As per the title, I have never quite understood the purpose of the strap between T5 and T6 in 700 series telephones. Without it, the gravity switch would disconnect the ringer when the handset is lifted, whereas this strap means that it remains connected across the line. Does this have an effect on the speech performance of the telephone during use, or is it simply a hangover from earlier telephones that didn't have a switch contact in this position? __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

27th Jul 2020, 5:45 pm	#2
dagskarlsen Heptode Join Date: Jan 2008 Location: Hakadal, Norway Posts: 532	Re: Why strap T5 to T6 in 700 series telephones? Seen from non UK (=Norway) I see no reason for that strap, but we have capacitors in each phone. (no master socket) dsk

27th Jul 2020, 5:55 pm	#3
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 4,978	Re: Why strap T5 to T6 in 700 series telephones? I don't think it's related to where the capacitor is located. After all, the 700 series of telephones pre-dates the introduction of master sockets with capacitors in them - and ringers were connected in series to avoid bell-tinkle when dialling. The thing that seems strange to me is that a changeover switch was introduced with the 700s (in contrast with the simple switch in earlier 'phones to make a loop) but the chageover contact was shorted out. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

27th Jul 2020, 6:15 pm	#4
OscarFoxtrot Heptode Join Date: Apr 2011 Location: Edinburgh, UK. Posts: 766	Re: Why strap T5 to T6 in 700 series telephones? The option may have been intended (whether used or not) for some plan systems where the ringer had to be rung (eg to signal an exchange call) even when the phone was in use (eg on an internal call).

27th Jul 2020, 6:35 pm	#5
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,394	Re: Why strap T5 to T6 in 700 series telephones? Isn't the link removed for shared service working? __________________ Regds, Russell W. B. G4YLI.

27th Jul 2020, 7:18 pm	#6
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,394	Re: Why strap T5 to T6 in 700 series telephones? I notice that on the cheaper ASTIC-less 'Etelphone' made by Ericsson (N1900) the paster diagram shows the link between T5 and T6 is removed. Drawing N112419/4 refers. __________________ Regds, Russell W. B. G4YLI.