Doug McNutt wrote: > At 15:36 -0800 11/12/09, David Wilker wrote: >> Any reason you couldn't use a simple step-down transformer, maybe 1:12?
That's all an AC output wall wart is. > > Anything from 7 to 10 VAC at 60 Hz would probably be acceptable. The galvanic > isolation provided by the transformer is probably required and probably needs > to meet some specification for connection to the telephone line. There is > probably an audio transformer in the telco line but it might not be > considered safe enough for the regulators. > The requirement for isolating circuitry that comes in contact with people is going to far exceed any requirements for isolation from the phone line. And yes, the phone line is isolated via transformer and opto-couplers and THAT isolation is sufficient for the phone line. If it weren't the phone line would be messed up simply by the ground via the computer and serial port, forget the modem's power transformer. > 6 VAC and 12 VAC transformers are ubiquitous. 9 VAC is not so common. It's fairly common, if for nothing else, modems. Most modems I've had have used 9 VAC. Make sure the current rating of the replacement transformer is the same as or more than the original BUT not too much more. If the current rating is too high then the voltage under the lower load will be quite a bit more than the spec. -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting "I'm a designated driver on the Information Super Highway" --~--~---------~--~----~------------~-------~--~----~ You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ -~----------~----~----~----~------~----~------~--~---
