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I recently acquired an early model Vic 20 computer but don't have a power supply for it and thought I might be able to make one. The Vic 20 is the early model with the two pin AC connector - not the later model DIN plug.

From what I've read it needs 9VAC at about 3A. I'm in Australia where mains is 240VAC, so I'm looking at this transformer:

http://jaycar.com.au/productView.asp?ID=MM2014&keywords=mains+transformer&form=KEYWORD.

It doesn't say on that site but in their dead-tree catalog it's got two sets out secondary outputs each multi-tapped 0->9V->12V, 2.5A each.

Since I've not done much with mains, just want to check somethings:

  1. Wiring the two secondary 0v + 9v outputs in parallel will give 5A output - enough to power the Vic and some accessories.
  2. Will I need a fuse on the mains side? They recommend one on the page so I presume so.
  3. What sort of case would you recommend for something like this - it's just the transformer and fuse, with a mains and 9VAC leads coming out. Should the case be ventilated, plastic, metal, how to best mount the transformer etc...
  4. Have I missed anything?
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    \$\begingroup\$ Upvote just for resurrecting a Vic-20! \$\endgroup\$ – Kaelin Colclasure Feb 13 '12 at 14:30
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  1. Check!
  2. There's discussion whether the fuse should be placed before or after the transformer. I place it before. I'd use a 500mA, slow-blow ("T") version.
  3. I would use a metal case rather than plastic. Not that there would be a risk of the plastic melting — it doesn't get that hot — but metal transfers the heat better to the environment. I would use a ventilated enclosure if I could find it, though it will cost a bit more.
    Mounting should be straightforward; if it's a classic EI transformer use a bolt and nut for all 4 mounting holes. Use spring washers so that the nuts don't come loose because of vibrations. A toroidal transformer often comes with mounting material, so use that.
  4. I don't think so. Success!
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    \$\begingroup\$ It's worth pointing out that you should connect the earth wire of the mains flex to the case, so that if somehow 240V makes contact with the case you will immediately blow a fuse/trip an earth leakage device. \$\endgroup\$ – Tom Davies Oct 31 '11 at 9:30
  • \$\begingroup\$ @Tom, I realized that, but good to mention it. \$\endgroup\$ – Brad Robinson Oct 31 '11 at 13:13
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The Commodore VIC-20 makes 9VAC available on the user port so that applications which need higher-voltage can employ a voltage doubler, but the VIC-20 would otherwise be just as happy with a DC supply of either polarity. Figure a drop of 1.4 volts for the rectifier and 2 volts for a 7805, an 8.4-volt DC supply would probably be ideal, with anything up to about 12 volts being tolerable. At least on my VIC-20, the 7805 generated a fair bit of heat; using a lower-voltage supply would help mitigate that.

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