6 Pwr Supply

So the first thing to do is find a decent transformer. I think the telephone exchange gods must have been smiling on me the day I started my search on eBay as pretty quickly found me a decent 240v to 36v/18v transformer for a reasonable price that would be just the job. A few days later it's mine and we are ready to go. 

For the 36v feed, DC conversion is via a bridge rectifier and ripple removal by use of a 1000uf capacitor which I think gave me around 44v DC. I used a LM317 VR. and arranged the resistors to give me pretty much 36v, as near to the required 40v on Andrews design as I can get. This is at the very limits of the VR but it seems to work ok. When I do get to connect a phone I do get a bit of hum but it's not too intrusive. I recently found out much better ripple rejection can be achieved using a capacitor multiplier, so maybe that's something for version III.  The other rectifier and capacitor are for the 18v feed that I'll use for the 5v components via a 5v VR. The Veroboard I have selected is 100 x 200 so should be big enough to hold the entire exchange circuitry, though this is always a bit of a guess at this stage. 



I'm planning to fit the whole thing in to this box so I'm keeping size in mind as I go about building the exchange.

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