Converting a US amp to UK

lovestrat74

What is involved or what is required to convert an amp made for the US market (110v?) to UK (240v?).  And roughly what would the cost be?

wjpp

Plug it into something like this https://boxed2me.co.uk/product/mercury-45w-230v-to-110v-uk-to-us-usa-voltage-step-down-converter-transformer-34669?gad_source=1&gclid=EAIaIQobChMIn8Dg6s7sgwMVFYdQBh1GcQv_EAQYBSABEgLIuPD_BwE

goldtop

wjpp said:

Plug it into something like this https://boxed2me.co.uk/product/mercury-45w-230v-to-110v-uk-to-us-usa-voltage-step-down-converter-transformer-34669?gad_source=1&gclid=EAIaIQobChMIn8Dg6s7sgwMVFYdQBh1GcQv_EAQYBSABEgLIuPD_BwE

Yes, but probably a bigger (higher VA) one than that. 45VA doesn't cover most valve amplifiers.

ICBM

lovestrat74 said:

What is involved or what is required to convert an amp made for the US market (110v?) to UK (240v?).  And roughly what would the cost be?

It depends on whether the power transformer has different voltage taps so it can be rewired. If it does, it’s a fairly simple job but it will need a new mains plug (ideally a new cable with the correct colour coding and a moulded plug) and a PAT check, so I would allow about £50.

If it doesn’t have a suitable transformer, you will either need to use an external step-down transformer (also about £50 for a decent quality one if the amp isn’t very low-powered), or have the amp’s own power transformer replaced with the ‘export’ version - this is a bigger job and more expensive, I would allow £100-£200 depending on the size and cost of the transformer.

If the amp is old and has a 2-wire non-earthed power cable this will need to be replaced as well, and the ‘death cap’ inside removed.

wjpp said:

Plug it into something like this https://boxed2me.co.uk/product/mercury-45w-230v-to-110v-uk-to-us-usa-voltage-step-down-converter-transformer-34669?gad_source=1&gclid=EAIaIQobChMIn8Dg6s7sgwMVFYdQBh1GcQv_EAQYBSABEgLIuPD_BwE

No, that is too low power-rated for all but the very smallest amps and doesn’t have an earthed output.

For most guitar amps you will need at least a 200VA transformer (for an amp up to about 50W), 300VA or 500VA (for up to 100W amps) - check the amp’s power draw rating - and it must have an earthed output socket (3 holes, but make certain it does genuinely have an earth connection and not just a blank hole).

Something like this - https://www.cricklewoodelectronics.com/230V-to-110V-UK-to-USA-Mains-Auto-Transformer-300VA.html

ecc83

All depends on the power consumption of the amplifier and how difficult the job of changing the power transformer will be. Not likely to be cheap.

Probably the simplest solution is to buy a suitable 'auto transformer' of the appropriate rating that way the amp stays 'stock'.

Dave.

rossi

Dear old Viv .I fondly remember a Bonzo song called " I'm painting my half of the drain pipe pink to keep the neighbours away"this always made mw laugh as there were several semis i around with exactly that ,the drain pipe painted their half  in their chosen colour often garish .

lovestrat74

Thanks all. The amp was an old Gibson GA-6 on Reverb but it has sold now

GoldenEraGuitars

lovestrat74 said:

Thanks all. The amp was an old Gibson GA-6 on Reverb but it has sold now

I was looking at a 58 Princeton the other day and funnily enough I asked the same question to my amp tech. No point in posting the reply from him but needless to say I’m much happier knowing what I’m looking at if dealing with a vintage American market model.

ecc83

Well, if we are talking "vintage" equipment, i.e. gear that is worth much more than its face value IF kept original, then do not even think of ripping out that septic traff!

Dave.

ICBM

With an original vintage amp - assuming it’s not already been modded or compromised in some other way - then the best solution is an external stepdown transformer. The only change you need to make to the amp is to replace the 2-wire power cable with a 3-wire and disconnect the ‘death cap’.

Some vintage purists might disagree with even doing this, but it’s important to remember that almost all stepdown transformers are autotransformers and not isolating transformers, so the amp is still directly connected to the mains and hence dangerous unless earthed.

goldtop

What he said. For the 40W 1960s Vibrasonic I use a big brick-sized external step-down TX, shown here just at the top left:



 It's a bit OTT at 500VA - because I use it for any/all US amps up to 100W output, and I prefer things to run cooler for longevity.

And I added that rather fat-sized three-pin plug with three-wire cable for proper grounding, when the amp had only a two-wire cable.

lovestrat74

Yes it was mentioned that the "death cap" had been removed.

ecc83

" It's a bit OTT at 500VA -" There is very little downside to going big! Obviously a bigger traff will run cooler but there are other benefits. The 'regulation' that is the stability of voltage with a varying load, will be better and if you run any transformer close to its VA limit it distorts the mains waveform and chucks out a lot more, more 'hashy' mains hum. In any case keep it well away from your guitar!

ICBM's point about "isolation" is worth repeating. There are isolating, step down transformers, usually called "tool transformers" used for 55-0-55 volt supplies in outdoor applications.

Iso-traffs watt for watt are bigger, heavier and more expensive than autos and you don't need them so LONG as that earth is carried through.

Dave.

allen

What about a modern amp? - say like a Mesa California tweed that's in the classifieds. What are the chances that it would have the necessary taps on the power transformer to just be rewired? Or what would the approx cost be to put a 240v power transformer in there?

ICBM

allen said:

What about a modern amp? - say like a Mesa California tweed that's in the classifieds. What are the chances that it would have the necessary taps on the power transformer to just be rewired? Or what would the approx cost be to put a 240v power transformer in there?

Many Mesa amps do have multiple taps, but if not then it will cost approximately one million pounds for the right replacement one from Mesa, if they'll even sell you one at all.

allen

Oh shame. If it was half a million I would have been okay with it.

allen

Seriously, there seem to be loads of mesa compatible transformers here:

https://www.tubeampdoctor.com/en/parts-for-amplifiers/transformers/mains-transformers/mains-transf.-for-mesa-boogie/

Does it have to be the 'exact' one? or surely one with the same specification would work.

ICBM

allen said:

Seriously, there seem to be loads of mesa compatible transformers here:

https://www.tubeampdoctor.com/en/parts-for-amplifiers/transformers/mains-transformers/mains-transf.-for-mesa-boogie/

Does it have to be the 'exact' one? or surely one with the same specification would work.

Yes, if they do the right one for the exact amp model. Some of them are quite complex though.

ecc83

For sure it needs to be the right one! Producing power transformers for amplifiers ( sstate as well as valve) is a bit of a 'Black Art'. You take a stab at how the voltages are going to pan out. Send the specs to the winders then when a pre prod comes back, test the arse off it. With luck it does what you expected it to but 25% of the time there will be an iteration.

All that is bad enough but when people want "world wide" operation it gets expensive and rarely bang on the money on in all countries. "The world" is not just 230 and 110 volts tha'knows!

LOT to be said for SMPSUs!

Dave.

Ddigger

ICBM said:

With an original vintage amp - assuming it’s not already been modded or compromised in some other way - then the best solution is an external stepdown transformer. The only change you need to make to the amp is to replace the 2-wire power cable with a 3-wire and disconnect the ‘death cap’.

Some vintage purists might disagree with even doing this, but it’s important to remember that almost all stepdown transformers are autotransformers and not isolating transformers, so the amp is still directly connected to the mains and hence dangerous unless earthed.

Could you not just use a power breaker between the transformer and mains socket?

ICBM

Ddigger said:

Could you not just use a power breaker between the transformer and mains socket?

Possibly - although I'm not 100% sure whether a RCD would still trip or not, since the current on the supply side of the stepdown transformer would still be balanced (or much closer to it).

I'll see if I can think of a way of safely testing this...