News:

"The phone is a remarkably complex, simple device,
and very rarely ever needs repairs, once you fix them." - Dan/Panther

Main Menu

GPO232 & Bellset 26 - Loud clicking in receiver

Started by Fennec, March 31, 2018, 08:43:42 PM

Previous topic - Next topic

Fennec

Hello, gentlemen:

I would appreciate your assistance in solving a loud clicking in the receiver of my GPO232 / 26 Bellset combo, that I hear every time the receiver goes on hook.

A while ago I have attempted increasing the impedance of the ringer by adding a 3k3 resistor in line, and a 2uF capacitor in series with original. While it worked, the clicking when going back on hook was like a small explosion. And after a while I suspect I blew up the magnet winding - total silence in the handset, although all other functions work...

Since I am not a phone tech, I can only assume that I have peaked the current in the receiver circuit enough times to essentially burn the winding.

I have since removed  both the capacitor and the resistor and replaced them with straps, per original wiring, but the clicking in the receiver is still there, although subjectively not as loud as before the failed mod.

Question - what could be causing the clicking in the original circuit? Is there a way to eliminate, or at least substantially reduce it? Also, is there a relatively non-invasive way to increase the impedance of the ringer and possible reduce the sidetone without negatively affecting the function of the phone?

Any advise would be appreciated.

Dmitri

twocvbloke

Rectifier 205, that was the official modification, it's connected across the receiver terminals in the phone, just take a couple of diodes (E.G. 1n4002), wire them back to back in Parallel with each other, and that's basically a Rectifier 205... :)



Edit to add picture of a DIY Rect. 205:

Fennec

OK, installed back a 3k3 resistor between B7 and B8, together with a "Rectifier 205" between T5 and T8, consisting of 2 x 1N4004 diodes. Clicks are still there, but much softer now, and so are soft clicks during dialing.

So, I'd say it worked - thank you.  :)

twocvbloke

Yeah, the clicks will remain, but they're much reduced in volume as not to cause acoustic shock (not a nice experience I can tell you!), which is handy for people who did follow-on calls without removing the handset from their ear... :)

dsk

#4
Regarding the pop, it may be wrong timing on the 2 hook switch contacts, I believe the one between terminal 1 and 8 on tour phone should open before the one between 2 and resistor winding.


Moving the extra capacitor from 2-3 to 4-5 may also help, of course you have to move the strap 4-5 to 2-3 at the same time.

Using a 0.67 uF capacitor instead of 2 uF, and using a strap instead of the resistor may increase the ringer volume with no or little increase of the REN load.


dsk

andy1702

There shouldn't be any requirement to put any additional capacitors inside a UK phone or bell box. The rectifier 205 is the correct modification and was commonly used on later 700 series phones. The 3.3k resistor is part of the conversion for UK plug and socket use. Anyone outside the UK using a traditional 2 wire system probably shouldn't need that either.
Call me on C*net 0246 81 290 from the UK
or (+44) 246 81 290 from the rest of the world.

For telephone videos search Andys Shed on Youtube.

dsk

Quote from: andy1702 on April 02, 2018, 07:46:45 AM
There shouldn't be any requirement to put any additional capacitors inside a UK phone or bell box. The rectifier 205 is the correct modification and was commonly used on later 700 series phones. The 3.3k resistor is part of the conversion for UK plug and socket use. Anyone outside the UK using a traditional 2 wire system probably shouldn't need that either.

I mainly agree, the extra resistor/capacitor will only be there to limit the pretty high ringer load, often wanted when the phone is used together with others on the same line, or when the ATA gets problems with such loads.

Different 1 kilo-ohms ringers has different impedance, and I have one telephone with a 1 kil-ohm ringer and 2 uF capacitor drawing so high ring current that my old sxs believes it goes off hook, but with another phone with the same values it works great.

The UK conversions with use of a resistor is by my opinion a cheap and not so good solution, but it has been a tradition in the UK. A resistor limits the load and has a considerable loss ending up in heating the resistor, but a capacitor adjusted to let the ringer circuit have the same impedance will have almost no loss of energy. Of course this is much more complicated to adjust, and you may not have any standard values to put in.

dsk

Fennec

Quote from: dsk on April 02, 2018, 08:35:57 AM
I mainly agree, the extra resistor/capacitor will only be there to limit the pretty high ringer load, often wanted when the phone is used together with others on the same line, or when the ATA gets problems with such loads.

Different 1 kilo-ohms ringers has different impedance, and I have one telephone with a 1 kil-ohm ringer and 2 uF capacitor drawing so high ring current that my old sxs believes it goes off hook, but with another phone with the same values it works great.

The UK conversions with use of a resistor is by my opinion a cheap and not so good solution, but it has been a tradition in the UK. A resistor limits the load and has a considerable loss ending up in heating the resistor, but a capacitor adjusted to let the ringer circuit have the same impedance will have almost no loss of energy. Of course this is much more complicated to adjust, and you may not have any standard values to put in.

dsk

I don't think there would be any harm in me trying to lower the REN by including a capacitor in series. Indeed, 3.3k was a "recommended" mod that I have found on UK phone forums, and it may well be a "poor man's high impedance" attempt. Having said that, since the 2nd cap would be in series with the original 2uF one, would it make a difference if it's between 2-3 or 4-5?

Also, you have drawn a blue wire, which in my phone I just connected to an empty E. On a NA 2-wire system, is there a reason why you would want to connect it to 3 ?

Dmitri

dsk

#8
Yes at this forum: https://goo.gl/KKqybH i found the picture under. there you see the third conductor working as a filter for the pulse contact, and discharging the capacitor(s). This will indeed reduce the pops in the receiver too.

This is also the reason for having the both capacitors on the same side of the third wire.

To reduce the REN load has been more and more common, and usually the ringing are still loud enough and gives a pleasant sound.  The original ringing was "harder" especially on short lines, I guess the intention only was to ensure enough signal to ring on good and bad lines.  Sometimes the resistor of 3k3  may stop a ringer from ringing.  Getting equal (and low) REN load on all telephones on the line will make it likely that all will ring and you may even have more telephones on a line.


Here in Norway we had a rule of maximum 2 ringers on the line, this rule was old and never explained.


dsk


PS I will guess that using a 0.67 uf capacitor will as the second will give you a chematic pretty equal to the lower picture.
DS

Fennec

OK, thank you twocvbloke, dsk and all for the input. Just to round this off:

1. Diodes across the receiver have helped to significantly reduce clicking, without affecting the sound level in the receiver
2. Installing 0.63 uF capacitor across 4-5 resulted in the phone being permanently on-hook, and phone ringing randomly, and only a couple of times.
3. Went back to original 2 uF capacitor, installed across 2-3, phone is ringing and receiver functions fine.
4. Re-tying the Blue wire to 3 did not produce any discernible effect, likely because there is no third wire in the socket that would "shunt" the AC to the ground. Left it at 3, since it does not seem to make any difference.

I would say that this is as good as it gets. Even though the REN number of the phone is impossible to calculate, a 4.3 kΩ load (1 kΩ coils and 3.3kΩ resistor) in series with 1 uF capacitance (2 x 2 uF in series) at 20Hz would result in ~9,000 Ω impedance. According to Wiki, this would be slightly under 1 REN (US standard).

Regards,
Dmitri

andy1702

If there is no 3rd wire in your line to go to the blue of your phone's line cord, then if the socket is a UK extension you might get different results if you xhange it for a master socket with a capacitor built in and a 3rd wire connection which is generated in the socket.

I run a 2 wire system here from a Revelation PBX, but all the extensions have to be master sockets to accomodate phones converted for the strange UK practice of ising a capacitor in the socket rather than the phone.
Call me on C*net 0246 81 290 from the UK
or (+44) 246 81 290 from the rest of the world.

For telephone videos search Andys Shed on Youtube.

twocvbloke

A cheat to getting the bell wire in a socket from a 2-wire extension is to use the ADSL microfilters that clog up our drawers of many things*, as the UK versions add back the bell capacitor and act like a mini PABX-Master socket... :)

I use them on my Panasonic systems as it's easier (and cheaper, cos they're freely supplied with modems & routers from ISPs) than setting up a master socket... :)





(*You know the one, the drawer that always seems to have everything but the one thing you want!!)