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Step Down Transformer (what's my best option?)

Thread starter #1
Hi there guys, I have a US Tube Poweramp that I want to use permanently in the UK...

Specifically it's a Peavey Classic 50/50 Stereo Tube Poweramp... it's power rating is:

500w
60hz
110v

And obv in the UK we are 240v, 50hz - will a simple 750w step down transformer do the job or will the hz difference prove to be troublesome?? Can you get hrz -converting transformers?? Or even a UPS might work if I get one that accepts 240v input into 110v / 60hz output??

What do you guys think is the best thing to do?? Thanks in advance!!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#2
No contest, just buy an auto-transformer - these are commonly (and cheaply) available - be aware that they don't provide isolation (but this isn't needed).

The mains frequency is of no relevence!, 50Hz and 60Hz are near enough the same.

A better option (but MUCH more expensive) is to source a UK transformer from Peavey - although you might try looking inside, just in case the transformer has alternative mains primaries!.
 
Thread starter #3
that's great, thanks Nigel - I will look into Auto-transformers and will look inside the amp and come back with my findings!

I am not bad with electronics but this is a new field for me!

I thought there might be frequency issues with it being a tube amp - but if not thats great news :) another load of my mind!
 
Thread starter #4
also would I be right in saying that it would be more problematic going to the US with a UK amp?? IE it wanting 50hz and getting 60hz?? going up would be worse than going down?? *ooo err* hehe...
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#5
Docaroo said:
also would I be right in saying that it would be more problematic going to the US with a UK amp?? IE it wanting 50hz and getting 60hz?? going up would be worse than going down?? *ooo err* hehe...
Again, it makes no difference, it's close enough not to matter - and you could use EXACTLY the same auto-transformer over there as well!.
 

eblc1388

Active Member
#6
It helps to know that whatever voltage and frequency you have chosen as the primary voltage, inside the amplifier internally it is converted first into DC high voltage using rectifier and capacitor to power the tubes. Tubes work on DC inside a stereo amplifier.

So small frequency difference has no audible effect on the sound quality of the amplifier.
 
#7
Docaroo said:
Hi there guys, I have a US Tube Poweramp that I want to use permanently in the UK...

Specifically it's a Peavey Classic 50/50 Stereo Tube Poweramp... it's power rating is:

500w
60hz
110v

And obv in the UK we are 240v, 50hz - will a simple 750w step down transformer do the job or will the hz difference prove to be troublesome?? Can you get hrz -converting transformers?? Or even a UPS might work if I get one that accepts 240v input into 110v / 60hz output??

What do you guys think is the best thing to do?? Thanks in advance!!
Used all my US equipment in Germany for many years, used a step down transformer and a different pulley on my turntable.
But I was thinking that you would maybe have about 120v from one of the hot wires to ground. Is so, you could just rewire your plug.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#8
Rolf said:
But I was thinking that you would maybe have about 120v from one of the hot wires to ground. Is so, you could just rewire your plug.
NO, NO, NO!!!!!!.

Don't attempt this! - Europe doesn't use the strange American dual-voltage system with two lives (a two phase system).

Europe use a three phase mains system with around 440V between phases, domestic premises only get a single phase supply, so you get a neutral (grounded at the substation) and a single live (230V), plus an earth lead (may be a local earth spike, or a PME earth provided by the electricity company).

So attempting the American idea would put 230V across the 110V transformer.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#10
Docaroo said:
lol not cool!! tis ok I shall go with the step down transformer! :) many thanks everyone!
One obvious place to get one (that you might not think of) is the bright yellow transformers used on building sites to feed electric drills etc. They use 110V electric equipment for safety reasons - because builders are completely brain dead where electricity is concerned!. So those big yellow portable transformers do exactly what you need - and you may be able to 'come across' one somewhere?.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#13
Dr.EM said:
Are you suggesting stealing one from a building site :eek: ;)
No :D

If you keep your eyes open you can often find them, as I mentioned builders are exceptionally brutal with their equipment, and quite often throw out 'faulty' transformers. Usually it's nothin more than a wire off inside!.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#16
Dr.EM said:
Yeah they are a bit unsightly, but unforunately the largest "black box" type one Maplin sell is only 300VA. eBay may have some offerings, the search term "110v transformer" brings up a selection of results :)
RS Components do them, but large transformers (even auto-transformers) are pretty expensive.

On a quick check Rapid do a 500W one for £36.98, or a non-ROHS 500W one for only £18.90, their on-site 3.3KW transformer is £39.00 which looks cheap next to the 500W one!.

You might also check toroidal transformers?, Rapid list a 55-0-55, which would give you 110V from the outside connections, 625W for £34.00 or 800W for £42.00, and £49.00 for 1000W. These would give you isolation as well.
 

Dr.EM

New Member
#17
Thats a good point, just pop them in a earthed case/plastic case and it would be relatively compact.

You say it provides isolation, does that mean you don't need to earth the secondary? I used to think they were Class2, but later found it never said that and so I have earthed the secondaries in thing's i've used them in (hence the ground loop on my hi-fi amp project and since earthing my power supply it has become far less useable). Are they safe to use without an earth at the secondary? They look pretty well insulated and I can't imagine the secondary ever going live in normal use, but heard there is always a chance unless it is doube insulated/class2 or whatever :)
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#18
Dr.EM said:
Thats a good point, just pop them in a earthed case/plastic case and it would be relatively compact.

You say it provides isolation, does that mean you don't need to earth the secondary? I used to think they were Class2, but later found it never said that and so I have earthed the secondaries in thing's i've used them in (hence the ground loop on my hi-fi amp project and since earthing my power supply it has become far less useable). Are they safe to use without an earth at the secondary? They look pretty well insulated and I can't imagine the secondary ever going live in normal use, but heard there is always a chance unless it is doube insulated/class2 or whatever :)
My personal opinions on earthing are well known on these forums, and they often don't agree with others! :D

Mostly people misunderstand the reasons for earthing, and blindly believe that something earthed is safer than something not earthed. Under certain circumstances this is true - but under many other circumstances it's more dangerous.

A LOT depends on exactly what you use the transformer for, and how the unit is cased - if you have a metal case it's probably a good idea to earth the case, this doesn't mean the secondary of the transformer needs earthing - it's a completely different scenario.

As for your power supply?, has it a metal case?, there seems little reason to want to earth any of the secondary side of the supply?, as you have already found out it makes it far less useful.

In the case of the valve amp under discussion, if you fed it from an isolated toroid there's no reason whatsoever to ground the secondary.

Construction wise it would be a VERY, VERY good idea to build the transformer in the amp (if there's room - if it's a combo, there will be plenty of room), otherwise you just know someone is going to plug 230V into the 110V transformer and blow it. You wouldn't believe how many items I see blown in this way!.
 

Dr.EM

New Member
#19
So, theres no real risk of the secondary going live anyway? I suppose it would take and full meltdown a the fuses would prevent that happening in any situation?

My power supply is in a plastic enclosure. The amp in a metal one (whose case is earthed as well as the secondaries). At the moment, the amp is used as amplification for my electric drum set, which is ran from an isolated wall wart so it causes no problems. The power supply though is very awkward with the earth, making it difficult to use with the scope as well as my mixer in the case of any audio circuitry. But being in a plastic case I guess it needs earthed secondaries? I had used it for months without, but by the nature of the equiptment I am often in direct contact with the low voltage output and a failure (no matter how unlikely) is certain to be very bad :D
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#20
The mains transformer provides isolation from the mains, and insulation failure between primary and secondary is EXTREMELY rare - even that VERY unlikely failure though is unlikely to be "very bad".

Personally I wouldn't have grounded the secondary, and I certainly wouldn't have grounded the scope either!.
 

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