ok, power supply question, 230v - 117v conversion

[aardvarkash10]

As I posted earlier, I havre bought four Rowe-AMI stereo jukebox amps. You should have seen the look on the cook's face...

Anyway, these are all ex-USA units and the power transformer is a 117VAC primary side unit. We are 230VAC in NZ. THe PTX is a beautiful lump with a centre-tapped HV, a 5V, and 2 x 6.3V windings. It looks like it could happly power the Ginza district.

Being a cheap and cheerful type, this has me more than a little upset. I could 1) replace the entire transformer - expensive, hard to source, and wasteful 2) have the transformer rewound - expensive and wasteful 3) run a 230VAC/117VAC transformer in front - expensive, ugly, more crap hanging around the AC outlet.

Then I thought about how to manage the 230VAC such that the transformer only sees 117VAC.

So, how about I half-wave rectify the 230VAC and feed that to the existing PTX?

Comments?

[DigitalJunkie]

So, how about I half-wave rectify the 230VAC and feed that to the existing PTX?

Nope. Transformers don't like (and won't work on) DC. Rectifying AC = DC.
With a half-wave rect. you'd end up with a half of a sine wave,and a DC component,and the transformers would not be happy at all.

[aardvarkash10]

but if you consider a half-wave rectified AC sine input, it is effectively a pulse transformer with a series of positive (or negative) pulses applied to the primary.

The only "DC" component (if you can call it that) is the period when the rectifier is not conducting, so there is no current. Would that still lead to core saturation?

[boywonder]

If you were going to operate them 2 at a time, you could wire the primaries for two of the amps in series........just trying to think outside the box.

[aardvarkash10]

of course, then I have to build it as a HT sysyem and that means building three more speakers and all that... Hey - grreat idea!

[theoldtrout]

I do all the electronic work for a guy who repairs, restores and imports juke-boxes to the UK. If there are no tappings on the main transformers I always fit a 230-115V transformer in the base of the box [there is always plenty of space]; it is the most safe thing to do. Don't forget to connect an earth [ground] lead to the metal chassis of the box.

Another issue you may have is that some boxes use a 60Hz a.c. motor to drive the turntable so the record will run at the wrong speed at 50Hz.

[Merlinb]

Originally posted by boywonder
If you were going to operate them 2 at a time, you could wire the primaries for two of the amps in series........just trying to think outside the box.

If the transformers are identical, it should be possible to run the primaries in series by the secondaries in parallel, yes? Observing correct phasing of course. More iron yes, but potentially one really powerful amp?