Telephone Switching > General PABX Talk

Miniature 10-line telephone exchange using 22 relays

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Owain:
The attached is an article from Wireless World, August 1980, by L D Gunn for a 10-line telephone exchange using 22 relays.

Please note the corrigenda from the Sept 1980 edition on the last page.

I would be interested to hear from anyone who constructs this circuit. I think the scan is legible but please ask if it's not.

GTC:
I found this site and this thread via Google.

Thanks for making the PDF of the article available along with the corrigenda.

I quite like the idea of building this little 10-line exchange, although miniature relays -- especially 48 volt ones -- are not as abundant these days as they were back in 1980 when the article was published, and their current pricing reflects this, too.

Also, it's very hard to find multi-tapped transformers these days, so I'd be looking to redesign the power supply around components more easily obtainable today, and at reasonable prices.

Given that we are dealing with rotary phone technology, a relay-based mini-exchange appeals to me far more than a microprocessor-controlled one.

I'd like to discuss this project with other members who may share this interest.

twocvbloke:
I recall seeing this exchange a few years back, looks quite intriguing, but beyond my abilities to construct, it would be interesting seeing one built though... :)

GTC:

--- Quote from: twocvbloke on August 20, 2013, 10:57:28 AM ---I recall seeing this exchange a few years back, looks quite intriguing, but beyond my abilities to construct, it would be interesting seeing one built though... :)

--- End quote ---

I think it's a great way to put 10 rotary dial phones to practical use, so I'm giving serious thought to constructing one.

Am in the process of working out the availability and cost of the various parts, especially the relays.

Owain:
I'm glad it's been found useful.

I also put up this article for a 2-line ringdown circuit / line simulator
http://www.classicrotaryphones.com/forum/index.php?topic=6141.0

IIRC when the original article was published, 'old' phones (probably Bakelite 300 series!) could be had for about 3 and 'new' phones (probably 706) about 5.

Mind you, a dot matrix printer for your 8K computer was probably about 1000 ...

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