KTAS D30 Rotary Phone

[Land Rover Fan]

Hello all,
I have just acquired a 1930s KTAS D30 telephone which I am in the process of converting to a standard bt plug.
This article has been very useful:
https://www.britishtelephones.com/pstconv1.htm
Scroll down, you’ll find it eventually! (Mine is the first version)

The the purpose of quick initial testing, (I don’t have a pulse to tone adapter yet so I will only be receiving calls) can I do without the resistor across the a/b contacts, until I can get my hands on one? I will also make sure to get a rectifier for the receiver.

I am quite a newcomer to all things old telephone related, especially ones from the other side of the pond!

[Dave Moll]

The insertion of the 3.3K resistor is simply a fudge to prevent a 'phone with 1K ringer from overloading the line if in parallel with other 'phones, so no problem leaving in the strap if the sole instrument on the line.

I take it from your comment about pulse-to-tone converter that your line doesn't accept loop disconnect (pulse) dialling.

[Land Rover Fan]

Originally Posted by Dave Moll

The insertion of the 3.3K resistor is simply a fudge to prevent a 'phone with 1K ringer from overloading the line if in parallel with other 'phones, so no problem leaving in the strap if the sole instrument on the line.

I take it from your comment about pulse-to-tone converter that your line doesn't accept loop disconnect (pulse) dialling.

Hello there,
Interesting you say that. I decided, for testing reasons, to leave the space for the resistor blank. What I got was quite interesting, was when I had got the phone working (hurray!) my GPO-67b telephone bell, which is connected to the same line, gave a single, DING when i picked up the handset. This got me thinking. My line is of the digital type, so the phone can’t dial out on its own, so when I dialed 0 for example, the bell rang until the dial returned to the stop position. The phones inbuilt bell didn’t ring, presumably because there was nothing between A/B, resistor or jumper. Either this is fine, or I have wired it wrong! The dial tone does get interrupted when I try to dial.

Edit: I have ordered the right parts, the resistor and the rectifier.

[Dave Moll]

Yes, if there is nothing between A and B, the bell will not be connected.

As to the ding on the external bell, are you using the anti-tinkle wiring of bells connected directly in parallel (via the third wire) or does each connect to the line via its own capacitor?

I don't understand the (external?) bell ringing while the dial is off-normal (i.e. during dialling).

[TonyDuell]

Originally Posted by Dave Moll

Y

I don't understand the (external?) bell ringing while the dial is off-normal (i.e. during dialling).

Could it just be the external bell tinkling due to the dialing pulses?

[Land Rover Fan]

Here is a video: https://www.youtube.com/watch?v=h6T9YxNukWw

I think the pulses from the dial are being picked up by the bell.

The same happens with the inbuilt bell.

Edit:
With another phone connected to the same line, if you lift the receivers on both phones and then dial on the old one, you can hear the pulses on the new phone. So theoretically the dial is working fine….

[Land Rover Fan]

Here is how I have wired it:

Please excuse my temporary wiring, I do have the original cable but haven’t connected it yet.

[Dave Moll]

I'll have a thorough look at Bob F's circuit diagram later (I'm presently only at home briefly), but it's probably worth trying with the A-B strap reinstated, as its removal may be disconnecting the suppression of the external bell. On the other hand you might end up with bell tinkle on both, but it would do no harm!

[Land Rover Fan]

Originally Posted by Dave Moll

I'll have a thorough look at Bob F's circuit diagram later (I'm presently only at home briefly), but it's probably worth trying with the A-B strap reinstated, as its removal may be disconnecting the suppression of the external bell. On the other hand you might end up with bell tinkle on both, but it would do no harm!

With it reconnected, the “dialing tinkle” is present on the internal ringer as well.

I have my GPO bell connected directly to my router, and I have been using this phone on the same line, though a splitter.

[Dave Moll]

OK, at least this proves that something is preventing the dial-off-normal contacts from shorting out the bells while dialling.

I must say that I'm not finding the circuit diagram the easiest to follow - not helped by yellow-coloured lines combined with my ageing eyes.

[Dave Moll]

I've now had a chance to study the circuit diagram (after going over the yellow lines with a ball-point pen!) and it's beginning to make more sense.

Although I'm unfamiliar with Danish, I assume from some knowledge of German that the four dial (nummerskive) wires are coloured blue (blaa), black (sort), red (rød) and yellow (gul). Assuming I'm correct (and with the 'phone not plugged in), are you able to measure the resistance between the red and yellow with the dial off its rest (normal) position, which should be zero. If tæller is (as I suspect) a 300 ohm resistor, this value of resistance should read between L2 and J (again with dial off-normal). I must say that I've not come across this arrangement and wonder whether this is allowing sufficient current to pass through the bells to cause tinkle.

[Land Rover Fan]

Hello,
Thank you so much for your research.

Between J & L2 is 1.33k (but this changes as I rotate the dial)

Between red and yellow on the dial is 300 ohms. As you suspected.

Attached is a photo of the underside of the telephone:

[Land Rover Fan]

There appears to be two resistors on the underside of the phone, could one of these need changing for a higher value?

[Dave Moll]

The smaller one at the back, 200 ohms, is presumably the one in series with the ringing capacitor, but the only 500 ohm resistance (larger in front, actually appears to be 510 ohm) in the diagram appears to be part of the induction coil. What's at the other end of the blue wires connected to it?

[dagskarlsen]

Take a look here: https://www.classicrotaryphones.com/forum/index.php?topic=19900.msg203907#msg203907

[Land Rover Fan]

Originally Posted by Dave Moll

The smaller one at the back, 200 ohms, is presumably the one in series with the ringing capacitor, but the only 500 ohm resistance (larger in front, actually appears to be 510 ohm) in the diagram appears to be part of the induction coil. What's at the other end of the blue wires connected to it?

The blue wires run from the larger of the two resistors to L2 and to a coil.

[Land Rover Fan]

Originally Posted by dagskarlsen

Take a look here: https://www.classicrotaryphones.com/forum/index.php?topic=19900.msg203907#msg203907

Interesting.

Mine is the slightly earlier version, but apart from the counter I believe they are quite similar electronically.

[Dave Moll]

Originally Posted by Land Rover Fan

The blue wires run from the larger of the two resistors to L2 and to a coil.

So that is the resistor next to the induction coil.

I must say that the circuit linked by Dags is much easier to follow - and not just because it's in English. By the way, now that I see tæller means counter, I'm not much wiser as to what it's doing.

[Land Rover Fan]

Originally Posted by Dave Moll

So that is the resistor next to the induction coil.

I must say that the circuit linked by Dags is much easier to follow - and not just because it's in English. By the way, now that I see tæller means counter, I'm not much wiser as to what it's doing.

I believe the counter was to calculate the telephone bill. Although I may be wrong…

[Land Rover Fan]

Ok, interesting development.
I have just acquired a second pulse dial telephone, and it too has “dialling tinkle”.
I have ordered a pulse to tone converter, so we’ll see if that helps.