Studio Monitor amp transformer mystery

Hi all,

I'm looking for some help regarding replacing the transformer of the power supply of my aging but beloved Event Electronics PS8 monitor plate amps.

One is buzzing, it's driving me up the wall. Delaminating transformer.

Nothing is written on them, Event itself doesn't exist anymore and I can't find anything spec-wise.

What some research has taught me is that if I know the voltage it is outputting, it's input voltage (230) and how many amps it should be able to deliver (0.5A@230 says the badge on the amp) I should be able to determine the transformer I need to replace them with, is that correct?

So I should open it up, power it up and measure output voltage, leg to earth and leg to leg? 

If for example its 2x 30v to ground and 60v leg to leg, I am looking for a 30V, 150 VA torroidal transformer?

Thanks for any help.

Thanks. 

Luckily the transformer still works, and I have a second to compare.

Yes the VA rating is a bit mystifying to me. Also I would like to go from this steel core vibrating junk to something like this. 

0.5A @ 230 is 115Watt. If it turns out to be 30V that works out to roughly 4 amps, so then I spec it slightly beefier it works out to 150VA.

But I'm unclear if this calculation stays the same if the transformer has 2x 30volt secondary. I'll open up the amp this afternoon.

A couple of things, Double check that it is only two windings and that there isn't a smaller pair that would supply the 15v for the input stage. Secondly you mentioned you are looking for a toroidial transformer, it is very rare that toroids buzz without outside intervention, loose clamps or covers. Check those before you go too far.

Don't worry too much about the current because if you get the correct voltage and correct physical size you can't go wrong, you can however go wrong if you select just current and voltage because it could be way too tall or look like a dinner plate and still be correct. You should be able to measure the ac voltage at the transformer or as it joins the board but you can also measure the dc voltage and divide the number by 1.414 to get the lower ac voltage.

It measures at 2x 27.4V at idle, so that would make it a 25V transformer I guess?

There is quite a bit of room so I think I will order two of these.

A pic of the transformer:

I ordered the transformers and I found the schematic.

In the manual it says the amp has turn on/off transient protection, but mine do like to emit a slight BANG when powering on or off.

Do you electronics wizards have an idea if I could fix that myself? It's not a huge problem because I rarely turn the off, but whilst I'm in there...