Classic Rotary Phones Forum

Telephone Switching => General Switching Discussions => Topic started by: dc4code on April 20, 2019, 03:15:29 PM

Title: How to create an Old Dialtone using Analog Electronics
Post by: dc4code on April 20, 2019, 03:15:29 PM
Is there any way to recreate an old sounding dialtone using modern off the shelf analog electronics ?

I know you can buy new vaccume tubes made for PreAmps, Is there any way I can combine those to create an Old City Dialtone?
Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: dsk on April 20, 2019, 03:56:50 PM
This is back-engineering, The first dial-tones was made bu a hum of the mains frequency, a buzzer, and later some resonant circuit(s).  Different development by different companies, no standards. 

dsk
Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: rherber1 on January 08, 2020, 10:47:43 PM
Is there any way to recreate an old sounding dialtone using modern off the shelf analog electronics ?

I know you can buy new vaccume tubes made for PreAmps, Is there any way I can combine those to create an Old City Dialtone?

Perhaps this could be a starting point http://oldphoneguy.com/old_dial_tone_main.htm
Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: Jack Ryan on January 09, 2020, 01:55:49 AM
Perhaps this could be a starting point http://oldphoneguy.com/old_dial_tone_main.htm

That article makes it sound complicated but in reality, it is not as simple as that.

The article states:
To be correct you need two sine wave oscillators with the 120 Hz one modulating the 600 Hz one, easier said then done. Search on Google for circuits, but there are not many.

That is not actually correct. The machines that generated old dial tone were not capable of multiplying two sine waves. They generally multiplied a noisy sine wave by a square wave so there were lots of harmonics in the "non precise" output.

It is possible to generate those tones and there was a lengthy discussion on the US CNet list that resulted in a micro-controller based tone generator. Bear in mind that the standard tones varied not only by manufacturer and equipment type, other countries used different tone frequencies.

Going back to the original request, what are the tones wanted for (how will they be played and where)? Can a recording be used instead of generating the tones?

So, it is possible to generate imprecise tones either roughly or "precisely". A uP based tone generator will be much simpler than an analogue circuit (which generally didn't use valves (tubes)). The complexity of the circuit will be determined by how fussy you are with the accuracy of the tones.

You will need a fairly simple transformer (perhaps even just a capacitor) based circuit to add the generated tone to your exchange if that is what you want to do.

Regards
Jack

Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: rherber1 on January 09, 2020, 05:02:12 AM
Hi Jack,

I make no claims for the validity or efficacy of the suggested 120/600Hz "Old DT Simulator" circuit and I submitted it only as a starting point for the OP to investigate. Since he was asking about "Old DT" I assumed he was wanting it for a vintage application and modern electronically or software derived solutions were not to be considered... But as you asked - "what is he trying to do with it?"

As for old dial tone - as far as Australia and the UK were concerned, this was 33Hz - or near enough. You are right that the inductor tone generator used to produce this dial tone produced many harmonics with the predominant ones in the low 200 - 400Hz range - and with appreciable level up to 1KHz. Without these harmonics dial tone would have been virtually inaudible since the receivers of the day (bell, 1L, 2P) had extremely poor response to a 33Hz sine tone.

Ross
Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: Jack Ryan on January 09, 2020, 10:00:16 AM
Hi Ross,

I understood that it was a suggested starting point and I in no way held you responsible for the contents of the article. I just added my take on the article.

I asked of the OP the purpose of the request in case a simple recording would suffice.

The discussion on the CNet list was a good one and I think the objective was to produce a kit although I have not heard anything since the prototypes were made.

Regards
Jack
Title: Re: How to create an Old Dialtone using Analog Electronics
Post by: Dan/Panther on January 09, 2020, 12:25:08 PM
Awhile back someone posted clips of dial tones from years gone by. Maybe that may help.

D/P