UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Two DSL filters, two 706 phones, bell tinkle

Riccardo Grillo · 13th Jul 2019, 9:30 pm

Andi,

Thank you so much for your reply, but I wonder if we aren't talking at cross purposes?

The bell tinkle noise comes not from the phone I am dialling on but from the other phone that is not being dialled on. One phone dialling causes the other to ring.

Yes, the filters do not have a third wire on their plugs, but they do have a third wire on their sockets so the phones can ring. My understanding is that the phone and its related filter (together) are essentially running as a two-wire device in that the filter only has 2 and 5 on the plug to the wall socket but that, instead of using its own capacitor, it is using the capacitor built into the filter. Essentially the filter is converting the 3-wire phone back to 2-wire?

I had heard of adding an extra switch, but I cannot see how this would work in the context of ADSL filters if this merely mutes the bell on the phone that is being used to dial out. What I'd need to do is mute the bell on the other phone, as it is the other phone that is ringing. Can you explain what you are thinking please as I'm not sure how I'd wire the bell, or how it would help in electrical terms?

Of course, the simple thing would be to run an extra cable from the router to a splitter plugged into the master socket, but that entails running an extra cable and more holes in the building.

I had a chat with a friend who used to do a lot of work with data cables and he said he wondered what the issue was with the 3rd wire is and whether it would only cause a problem when the phone rang, which I could happily live with.

In practice, my extensions all have the third wire and so it is presumably normally at -48V and would become highly charged when a ringing voltage is applied and cut to wires AB, but since no phone is connected to that wire, there is no current.

Any thoughts on my original suggestions above?

I have also had another thought. If the issue with having a bell wire is that it takes its negative from 2(B) at the master socket and dumps its positive back onto 5(A) thus meaning that the AB pair is not balanced and that the bell cable is not balanced at all, would it somehow be possible to add a 4th wire (4) (that lovely spare green wire) to take the positive from the bell in the phone and connect to 5(A) at the master socket straight through the filters?

Thus:

https://beta.photobucket.com/u/ricca...a-614b66419588

This would mean that the ringing current would run down 3, return to the master socket along 4 from whence it would continue along A, thus, hopefully, not inducing a current or unbalancing BA on the internal wiring.
I'm guessing the reason they don't already make filters like that is that most phones would not work on them... but we can modify a 706 quite easily.

What do people think?

13th Jul 2019, 9:30 pm	#4
Riccardo Grillo Triode Join Date: Jul 2019 Location: Colchester, Essex, UK. Posts: 24	Re: Two DSL filters, two 706 phones, bell tinkle Andi, Thank you so much for your reply, but I wonder if we aren't talking at cross purposes? The bell tinkle noise comes not from the phone I am dialling on but from the other phone that is not being dialled on. One phone dialling causes the other to ring. Yes, the filters do not have a third wire on their plugs, but they do have a third wire on their sockets so the phones can ring. My understanding is that the phone and its related filter (together) are essentially running as a two-wire device in that the filter only has 2 and 5 on the plug to the wall socket but that, instead of using its own capacitor, it is using the capacitor built into the filter. Essentially the filter is converting the 3-wire phone back to 2-wire? I had heard of adding an extra switch, but I cannot see how this would work in the context of ADSL filters if this merely mutes the bell on the phone that is being used to dial out. What I'd need to do is mute the bell on the other phone, as it is the other phone that is ringing. Can you explain what you are thinking please as I'm not sure how I'd wire the bell, or how it would help in electrical terms? Of course, the simple thing would be to run an extra cable from the router to a splitter plugged into the master socket, but that entails running an extra cable and more holes in the building. I had a chat with a friend who used to do a lot of work with data cables and he said he wondered what the issue was with the 3rd wire is and whether it would only cause a problem when the phone rang, which I could happily live with. In practice, my extensions all have the third wire and so it is presumably normally at -48V and would become highly charged when a ringing voltage is applied and cut to wires AB, but since no phone is connected to that wire, there is no current. Any thoughts on my original suggestions above? I have also had another thought. If the issue with having a bell wire is that it takes its negative from 2(B) at the master socket and dumps its positive back onto 5(A) thus meaning that the AB pair is not balanced and that the bell cable is not balanced at all, would it somehow be possible to add a 4th wire (4) (that lovely spare green wire) to take the positive from the bell in the phone and connect to 5(A) at the master socket straight through the filters? Thus: https://beta.photobucket.com/u/ricca...a-614b66419588 This would mean that the ringing current would run down 3, return to the master socket along 4 from whence it would continue along A, thus, hopefully, not inducing a current or unbalancing BA on the internal wiring. I'm guessing the reason they don't already make filters like that is that most phones would not work on them... but we can modify a 706 quite easily. What do people think?