Selecting a Power Transformer for a Korg Trident - VA & Power Factor Questions

Dear GroupDIY,

I'm looking to modify a British (240V/50hz) Korg Trident to run on US (120V/60hz) power by replacing its power transformer. Typically I would look up a data sheet for the transformer or use a step up transformer and take measurements but without either of those available I'm hoping to find a suitable replacement by making a few educated guesses.

The calculations should be simple but moving between Watts and Volt-amps (VA) psychs me out and I'd love to hear any insights. Hopefully I'm not overlooking something!

First, I wanted to figure out what kind of secondary voltage I need to look for. The keyboard has a linear power supply with custom regulators that supplies +/-15V and +/-5V (see attached). I disconnected the original transformer and ran a 24VAC sine wave into the primary and measured a 4VAC wave on the (unloaded) secondary to so with that ratio remaining constant I assume I'm looking for a transformer with at 36VCT or 40VCT secondary coil which would give each rail ~18-20VDC of headroom to regulate down to +/-15V.

The next step (and my main question!) is to figure out how big of a transformer I'd need. The service manual says that this keyboard consumes 53W of power so I know I'm looking for a transformer with a Volt-Amps rating of at least (and probably more than) 53VA, but how big is big enough?

I could base a conservative guess on the main line fuse but the fuse is rated at 2A so 2A*240V=480VA which seems way too big for the instrument. Alternately, this website suggests a way to calculate the VA for a similar power supply which comes down to: VA = 1.4 x ( WATTS + 2 IDC ) where IDC is the DC current output. This power supply has a 3.15A fuse for each rail so it seems my calculation would be 1.4 x (53W + 2(6.3A)) = 91.84VA which looks more reasonable although still pretty big. Is that a fair estimation?

Whats the best way to make this calculation so I don't end up with a transformer that's too big to fit in the instrument or so small it burns out?

It seems your transformer has 40V CT.

If the device consumes 53W then the current requirement is just over 1.3A.  With a little extra call this 1.5A. You'll need a charging current of between 50 to 70%. With a bear minimum you are looking into 2.2A. So, your estimation of around 90VA is reasonable. 

Check the available space within the instrument. Check the transformer dimensions and if you can get higher VA rated one in, then why not?

are you experienced? have you ever been experienced? 

if so you could measure the pri current of the Korg with everything on, radio, heater, wipers, rear defroster, this will tell you your actual pwr consume,  it may vary wildly from the sticker plate,

multiply you current by the line voltage that evening and there is your VA.

pwr factor not really an issue as this is mostly a resistive load,

maybe you mean duty cycle?

getting a spell check error on resistive, wtf, over?