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Vintage IMAI.S.S. Power Supply Voltage Conversion

I've recently returned from Japan and have brought a loot with me. Whilst in Tokyo, there was the annual Antiques Jamboree at Odaiba and I happened across a box of HO KTM brass that I could not refuse.

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This set included a lot of track, two powered locomotives, rolling stock and a power supply. Thanks to the age of the kit, the power supply was 110v only. Preliminary testing in my Tokyo hotel proved that everything was in fantastic working order. I assume this box has been in someone's cupboard for quite a while.

Don't plug anything rated at 110v into Australian sockets

You don't want to try this at home. Our powerpoints are more than double the voltage of that in Japan... I wonder if this explains why we have a ground line. Either way, any Japanese equipment that is not dual-voltage will bake if you plug it in. This beautiful old transformer would never handle it's new home.

I had the option of chaining in a power converter, but this would have been tedious. In fact, this is my first 110-only product and I would've needed to purchase a step-down transformer. Instead I chose to pull the thing apart and replace the transformer.

What were you expecting? Integrated Circuits?

I opened up the power supply and felt that I'd opened a treasure chest. I could pick out the potentiometer for the throttle, the switch for the direction and the transformer. The final component needed to be a bridge rectifier to convert the AC to DC, but it ... didn't look like one at all.

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Following the wires, it seemed that there were 5 contacts on the device I assumed was the rectifier. A little googling informed me that this is a vintage metal rectifier with selenium insulation acting as the diodes. Very cool actually.

Purchasing a replacement transformer

Jaycar is my local electronics store of choice (if not the last available store in Australian cities) and perusing their site came up with a valid substitute.

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There were quite a few to choose from, actually. As the amperage went up, so did the weight. I assume the copper coil mass dictates how much current the transformer can deal with.

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Transformer transplant

This all went quite swimmingly. The existing wiring was labelled for safety-sake.

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It turns out that the 110v input wires were hardly twisted and taped together. I would hope that this wasn't an original factory job... but as far as I know this is a Japanese brand and this should have been the original factory plug. Quite interesting... let alone dangerous.

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Once the 110v transformer was out, the new transformer was soldered and then bolted in.

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It just fit. I mean.. a few millimeters more and we would've had to determine if Jaycar does returns.

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The 240v feeder was passed in and the wires were heatshrinked, the rest were soldered in place as per the previous construction.

Plugging it in...

With breath held, I plugged the transformer into the power board. It worked. The light lit dimly and no smoke came out.

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I rigged up a quick test track from the box of treasure purchased in Japan and tested the KTM ED100 that also came with it. After a little wheel and track cleaning the locomotive started bolting along.

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Success! This transformer is solid... although has zero short-circuit protection! Smoke started to appear during a motor short.. but I couldn't determine the source... I'll make bloody well sure in the future that shorts don't last too long.

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The directional switch is momentary unless you force it to either extremity. This is a nice touch as you can set your speed and then pulse the direction as required.

After running my brass EF62, I found a screw left on the track... the downfall of brass locomotives is that they're bound to shake things loose eventually!

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I was nothing short of ecstatic to have found this box at the antique fair in Tokyo.

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About stevenh

Trains… trains… trains… + Electronics + Japan.

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