On 15 Feb, 08:25, Frank Erskine wrote:
On Sun, 14 Feb 2010 15:25:22 -0800 (PST), Hugh



wrote:
On 14 Feb, 11:35, "Tinkerer"
wrote:
"Hugh" wrote in message

....

On 13 Feb, 16:37, JohnW wrote:
On 13 Feb, 12:24, Hugh wrote:

The problem is, when the phones go off-hook, the bell goes ding,
presumably because the sudden change in line voltage goes through the
capacitor and into the bell.

Hugh

You need to put a thermistor in series with the bell. These were very
common when I worked for the Post Office and looked like this:

http://www.telephonesuk.co.uk/images/1A-1.jpg

A quick Ebay doesn't show any for sale, but there were so many used,
there must be some around

John

Thanks very much for the tip, John. *I can see how that would work..
I'll keep a watch for one.

Any good?http://www.maplin.co.uk/Search.aspx?...stor&source=15
--
Tinkerer

Thanks for that. *Maybe the 15k thermistor might be worth a try.

The GPO "Rate Book" (a sort of catalogue of stores) specified the
Thermistor 1A (the 'innards' of the 1A-1) as having a cold resistance
of 200,000 ohms +/- 20%, and a hot resistance (with 100mW) of 500
ohms.

--
Frank Erskine


Thanks Frank, that is very useful information. The 1A thermistor has
a very wide range. I've ordered a a couple of the two suitable
thermistors Maplins sell:

The FX22Y is 1.19k at 100C, 15k at 25C and 45k at 0C
The FX42V is 2.94k at 100C, 47k at 25C and 155k at 0C

I'll report back how these perform with the old bell.

Cheers,
Hugh