International Amp Conversions

[DJSC89]

Gday everyone, im really happy i finally tracked down a forum here where i can ask questions no one else can answer.
The search that led me here is all about being able to successfully modify U.S tube amps so they can run in australian power conditions (240VAC @ 50-60HZ)
My previous attempt was only partly successfull and it really discouraged me.
I tried to convert a U.S made Peavey 5150 mkII, i changed the existing power transformer with a torrodial transformer which i thought would disperse any noise, i think it induced a hum in the amp because it wasnt in a casing??
anyway, the Xformer was 240v primary with a 110v secondary so it did work and the amp worked well it was just too noisy and the person i did it for took it to an amp guy who charged a heap and fixed it up while making me look the fool.
Im now interested in getting a US dual rectifier and changing it so it will work here in australia without the need for an external power transformer.
Is there any specific things i need to be doing apart from getting a 240v to 110v transformer??? and where can i get one?
any help would be appreciated.

[Enzo]

Are you talking about adding a 240 to 120 transformer ahead of the existing power transformer inthe unit? The way to do this is replace the existing power transformer outright, with one having 240v primary windings. All the secondaries would be appropriate then. You don;t want two transformers in there.

It is not clear what you did. On the one hand you state you replaced the power transformer in the amp (which to me means removing the original one completely), but next you say your new transformer has a 110v secondary. The PV amp does not use a 110v winding on a secondary circuit. That makes me think the original one is still there, but running off the other transformer instead of direct off the mains. Which is it?

When you talk about noise, it would be a good idea to differentiate between noise and specificaly hum. Hum is noise, yes, but itis a particular type of noise that would associate with transformers, as opposed to pops and crackles and hisses, and so on.

[DJSC89]

Are you talking about adding a 240 to 120 transformer ahead of the existing power transformer inthe unit? The way to do this is replace the existing power transformer outright, with one having 240v primary windings. All the secondaries would be appropriate then. You don;t want two transformers in there.

It is not clear what you did. On the one hand you state you replaced the power transformer in the amp (which to me means removing the original one completely), but next you say your new transformer has a 110v secondary. The PV amp does not use a 110v winding on a secondary circuit. That makes me think the original one is still there, but running off the other transformer instead of direct off the mains. Which is it?

When you talk about noise, it would be a good idea to differentiate between noise and specificaly hum. Hum is noise, yes, but itis a particular type of noise that would associate with transformers, as opposed to pops and crackles and hisses, and so on.

i see how i mislead there.
i did put the transformer in the head as a step down transformer, so it went 240VAC into the transformer i installed, 110v out and through the fuse, which i then assume went to the power xformer in the unit.

the scenario im asking about now is if i get a australian type dual recto transformer will it be as easy as just connecting straight in where the U.S power xformer is?

and by noise i did mean hum, sorry i am quite new to this but i do want to expand my knowledge, im a electronics technician by trade but tube amps seem to be a whole different world.

[black_labb]

what you had done should work correctly. the issues that could have caused the hum is where the transformer is on the amp and where the wires are running. the idea is to get it as far from the preamp as possible and keep the wires as short as you can. putting it close to the power transformer should be a good start.

a photo could help

[Enzo]

Yes, adding a step down in front should work, but putting a second power transformer inside the amp is asking for more hum coupling at the very least, not to mention the added weight.

[DJSC89]

yea it did add alot of weight and the wires were long and i did have the step down transformer bolted to the inside roof of the head if that makes sense.
Is it easy to get a power transformers that will be able to mount in place of the one in the U.S model dual rectifiers? and is it just a matter of changing the one in the U.S model for a australian one, i guess what i mean here is if there is any extra circuitry or components required ?

help so far has been amazing too thanks, ive learnt more off here then i wouldve in 100 yrs alone

[Enzo]

COntact customer service at Peavey, they will send a schematic. Seems to me it includes the variations on mains. The secondary voltages will all be the same of course, the primaries will be set for 240. Ther are some minor changes like removing the polarity switch and a couple caps on the mains side.

I don;t know what they cost or how hard they are to order down there, but a Peavey 5150-2 power transformer is what it would take. Down under, I suspect they only sell the kind you need, as there would be little market for new 120v ones.

Or if you are now talking about a Mesa, same formula.

[Steve Conner]

You usually get one of two possibilities:

1. A universal power transformer. The amp is sold with the same transformer everywhere in the world, and it has several primary windings that you wire up however you want. This is easy to convert, you just flip the voltage selector from 115 to 230. Or if there's no selector, you open the amp up and rearrange the primary connections. Often they print a little diagram inside the amp, showing how to hook the windings up for various voltages.

2. Two different transformers depending on the market. For amps to be sold in the USA, the maker fits a 120V, 60Hz only transformer, to save money. For export models, he fits a 240V transformer.

If you have an American amp with the 120V transformer for the domestic market, and you live in a 240V country, you need to order the export transformer and swap it out. I think Mesa (and Peavey too) are the kind of company that you could call up and explain what you're doing, and they'll take your amp's serial number and make sure to sell you the right part.

Or you could get one from TAD in Germany.