VoIP ATA Tinkle Thermistor 1A - UK Vintage Radio Repair and Restoration Discussion Forum

boombox · 16th Apr 2020, 8:55 pm

At least once a day I hear a GPO phone do a bing, bong - sounds like the beginning of a ring- only it never goes full throated, never gets beyond the initial two or sometimes three notes. Quite jarring because it sounds JUST like the beginning of a ring.

Anyway I was doing some reading about this and it sounds like a solution IS available (although I am wondering why my phones, which were both in use on the PSTN, weren't/aren't retrofitted with this) - the thermistor 1A?

I've had a look online and these are being sold at £6ea which seems very steep for what is probably a few pence worth of component.

Interestingly, but logically, I didn't have this problem when I had both GPO phones on one port of the ATA, now that I've got each phone on its own port, the bell tinkle has reared its head.

So just wondering if you guys had any tips before I ponder splurging the £6... which I can't really bring myself to do...

Thanks!

Cobaltblue · 16th Apr 2020, 10:22 pm

Some information from Sam Hallas amazing site.

The present standard method of preventing bell tinkles is merely to connect a thermistor in series with the bell coils. A thermistor is a special type of resistor with a high negative temperature coefficient; in this instance it has a nominal resistance of 200,000 ohms when no current is flowing through it, and the resistance drops to less than 500 ohms When it is passing a steady current of 14 mA.
The durations of the surge voltages caused by dialling or other signalling conditions are too short to lower the thermistor resistance appreciably, so that insufficient current will pass to operate the bell.

I am guessing you could get away without such a wide range by experiment

Cheers

Mike T

Graham G3ZVT · 17th Apr 2020, 9:35 pm

I would want to tackle the cause rather than the symptom. Is the ATA configured with a static LAN IP address or does it get one via DHCP? If the latter, what is the lease time?

Another thought!! does any phone connected to the ATA have a voicemail checking facility (obviously not the GPO phones)

Might help if we knew the model of ATA.

16th Apr 2020, 8:55 pm	#1
boombox Pentode Join Date: Mar 2012 Location: Rotherham, South Yorkshire, UK. Posts: 152	VoIP ATA Tinkle Thermistor 1A At least once a day I hear a GPO phone do a bing, bong - sounds like the beginning of a ring- only it never goes full throated, never gets beyond the initial two or sometimes three notes. Quite jarring because it sounds JUST like the beginning of a ring. Anyway I was doing some reading about this and it sounds like a solution IS available (although I am wondering why my phones, which were both in use on the PSTN, weren't/aren't retrofitted with this) - the thermistor 1A? I've had a look online and these are being sold at £6ea which seems very steep for what is probably a few pence worth of component. Interestingly, but logically, I didn't have this problem when I had both GPO phones on one port of the ATA, now that I've got each phone on its own port, the bell tinkle has reared its head. So just wondering if you guys had any tips before I ponder splurging the £6... which I can't really bring myself to do... Thanks!

16th Apr 2020, 10:22 pm	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,867	Re: VoIP ATA Tinkle Thermistor 1A Some information from Sam Hallas amazing site. The present standard method of preventing bell tinkles is merely to connect a thermistor in series with the bell coils. A thermistor is a special type of resistor with a high negative temperature coefficient; in this instance it has a nominal resistance of 200,000 ohms when no current is flowing through it, and the resistance drops to less than 500 ohms When it is passing a steady current of 14 mA. The durations of the surge voltages caused by dialling or other signalling conditions are too short to lower the thermistor resistance appreciably, so that insufficient current will pass to operate the bell. I am guessing you could get away without such a wide range by experiment Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

17th Apr 2020, 9:35 pm	#3
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,715	Re: VoIP ATA Tinkle Thermistor 1A I would want to tackle the cause rather than the symptom. Is the ATA configured with a static LAN IP address or does it get one via DHCP? If the latter, what is the lease time? Another thought!! does any phone connected to the ATA have a voicemail checking facility (obviously not the GPO phones) Might help if we knew the model of ATA. __________________ -- Graham. G3ZVT