On Feb 20, 9:09*am, Hugh wrote:
On 18 Feb, 02:10, "Dave Liquorice"
wrote:





On Wed, 17 Feb 2010 05:43:50 -0800 (PST), Hugh wrote:
If you study the circuit diagram for a traditional dial telephone,
and
an actual dial, you'll find that on the dial, as well as the
clever
pulsing mechanism there are two additional pairs of contacts which
'make' when the dial is 'off normal', ie away from its rest
position.

One of these is used to short the handset earpiece to
prevent/reduce
clicking in the receiver; the other is used to shunt
(short-circuit)
the bell.

Ah it comes back now... yes it was dial switches that shunted the bell to prevent clicks and tinkles.

It might be worth checking that the wiring is correct, though
IIRC
you either get bells that ring non stop or don't ring at all.

Sadly, I think that the current NTE5 (modern plug-socket system)
is
Fairly Bad News for enthusiasts of electromechanical bells and
pulse
'dialling', since there's no provision for series bells with their
positive anti-tinkle circuitry.

The bells are in parallel between the anti tinkle/bellwire and one of
the line wires. The anti tinkle is feed via a C from the other line
wire. If you short the anti-tinkle to the line wire that has the
other side of the bells they won't tinkle and the C maintains the DC
line conditions for pulse dialling.

I used to have a proper bell and didn't have trouble with it
tinkling. I think that Decor 1200 isn't shorting the bell wire as it
should. The mechanical solution may well be the best option. See if
you can work out which way the hammer moves when a phone goes of hook
and bias it that way against the gong. Not too much or you'll damp
the gong to much when a real ring finishes. Or as the gongs have
offset holes just try rotating them at little to adjust the relative
positions of them and the hammer.

--
Cheers
Dave.

Want to follow-up on the excellent suggestions from Terry and Dave.
Your ideas certainly tie up with what happens in practice, in that the
size of the ding varies quite a bit, and is obviously dependant on
where the striker is resting relative to the two gongs when the pulse
comes on the telephone line.

Brilliant idea to bias the striker against the gong that will sound
when the phone goes off-hook. *The two gongs have very slightly
different pitch so it's easy to identify the direction. *The only
problem I could see is that while you might be able to suppress the
ding when the phone goes off-hook, during the time the phone is
checking for 1571, the ringing capacitor will charge to the new line
voltage, and when the phone goes on-hook, a pulse will be produced in
the opposite direction so a ding will sound from the other gong.

Anyway, I biased the striker to the first gong with a rubber band,
initially I had too much force and the bell wouldn't ring at all.
With a gentler tension applied near the bottom of the striker arm
near the pivot, the results were much better. *I took out the
thermistor and replaced it with a 2.2k ohm resistor (roughly the right
value I think for a REN of 1 with this old bell) so I now have a
better ring. *With the elastic band, there is now no sound at all as
the phone goes off-hook and only the faintest ding when the phone goes
on-hook. *Obviously the rubber band is sufficient to resist the
limited energy stored in the ring capacitor.

The rubber band is a sort of temporary fix, as these things perish and
change resilience, so I'll need to look around for a weak coil spring
to replace it now that we seem to have come up with a satisfactory
solution.

Thanks again for all your interest and invention, even all the way
from Canada!

Cheers,
Hugh- Hide quoted text -

- Show quoted text -

Thanks Hugh. We used to have the ding problem, occasionally with dial
phones. Today touch-tone is just about universal (see anecdote). As
mentioned there are extra contacts on the dial to shunt out the
'speech portion of the telephone circuit' and the perhaps disconnect
the bell, within the same phone, while dialling takes place.
When however there is a separate magneto phone bell; as mentioned in
the original posting, and not being familiar with today's GPO phone
connections (Oops that's Brit.Telecomm these days isn't it?) it seemed
like the 'mechanical' approach might be appropriate?
Also I have two of those big magneto phones downstairs; always meant
to modify one so as to answer the touch tone phone line when in the
workshop.
Anecdote: Grandson to school friend visiting briefly after school one
day! "Hey have you seen this cool phone! It's got this round thing to
dial numbers!". Then; "Hey Pop can I call somebody on it?".
The same grandson, when many years younger, was seen pressing the
numbers on calculator while pointing it at the TV! Today he can load
and/or programme a computer faster than I can.