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petemck66 20th March 2015 07:00 AM

240v to 110v for Sun Valley JB-300B
I need to know what wattage step down transformer I need for a Sun Valley JB-300B valve amp (110v) from Japan. stepped down from Australian 240v. Also any information on it would be good, as there does not seem to be a lot on the net as far as I have found so far.
Any help appreciated


Gorgomat 20th March 2015 07:49 AM

Did you try to check one of the PDF available ? Though I cannot read japanese, I can still calculate the power needed by the transformer by simply looking at the voltages + max. ampere for each coil.

You might need a step down transformer which can handle about 220 VA ;)

Best regards,

jeffhigh 20th March 2015 08:56 AM

If there is a mains fuse, I'd be giving some margin over the fuse rating X 110.

tubetvr 20th March 2015 10:14 AM

Note that Japanese mains voltage is 100V not 110V so if the amplifier is made for the Japanese market you will need a step down transformer from Australian 240V to 100V, using a transformer with 110V secondary will put unnecessary stress on tube heaters.

kevinkr 21st March 2015 12:18 AM

As tubetvr points out Japanese mains voltage is 100V and is commonly 60Hz (although 50Hz is or was used there too). Make sure that the amp's power transformer can operate on 50Hz (probably not an issue)

Growing up overseas we commonly used 1kVa auto-transformers to power loads of up to about 400Va which maintained better regulation that a smaller sized transformer would under varying loads.

tubetvr 21st March 2015 09:03 AM

50Hz is used in Eastern Japan like Tokyo and 60 Hz in Western Japan like Osaka.

The issue with voltage being 100V in Japan and not 120V which is standard in US is often overlooked and sometimes result in problems, In Japan they sell transformers for 100V in and 120V out for driving sensitive equipment built for 120V.

petemck66 22nd March 2015 08:52 AM

Thanks for all replies, looks like I will have to do a little more research, but I have a bit more of an idea now, so thanks again.


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