Step down transformer recommended

[overales]

Hi all,
I've purchased an early 70's Ampeg B15 portaflex from the US.
While waiting to get it home, i'm looking for a step down transformer to convert the 120VAC to my home's 230 voltage.
I can find many different options out there, some are big and bulky, some others smaller.
The amp has 30 watts all tube, and runs 50/60Hz.
Which one will be the safest i must look at?
Will much appreciate your suggestions, and sorry if there is some other thread with the same question, just couldn't find the right one for my understandings.
Thank you!

[iiipopes]

Stepdown transformers are not recommended, especially with running with other gear. There are numerous noise, hum and shock hazard reasons why.

I recommend you contact Ampeg to obtain a replacement transformer at UK mains voltage.

[bremen]

You need to know the power consumption of the amp, rather than its output. This will be considerably more than the output, and should be stated on a label somewhere on the chassis.Once you know this, choose a transformer at least that rating, try Farnell or Rapid Electronics.

I know of no safety issues with using a step-up, care to elaborate, iipopes?

[The fasting showman]

I can't see a problem with using a stepdown either, as Bremen has said, once you've established the consumption which won't be huge I'd guess.
I owned a USA '70s Ampeg v4B that I sourced a replacement UK mains transformer for from Fliptops in the US; this was only because I was sick of dragging a heavy stepdown around along with a heavy amp. It was an easy drop in for our local amp tech. I'm stating the obvious, I don't mean to insult your intelligence: keep the original transformer in case you sell the amp on if you go down the route of switching out the mains transformer.

Edited August 26, 2013 by The fasting showman

[overales]

Thank you all for your responses.
I know that fliptops.net has replacements to power transformers for vintage B15's.
I'm planning to end up ordering one of these but the whole price plus shipping and tax duties are expensive, so i wanted to try a step down one to fire up the amp once gets home.
Contacted Ampeg and recommends me any transformer that can step down 120V and can supply at least 100 watts.
I will check for the brands you are suggesting.
Thanks again!

PD. I only have some pics at the moment and can't see any label on the chasis either than than the 120VAC 50/60Hz and AC Outlet 500 Watts Max
Better to wait until it arrives.

Edited August 27, 2013 by overales

[iiipopes]

Grounding and earthing issues. Old American amplifiers can have the white or neutral side of the mains plug wired across the amplifier chassis, dually functioning as the ground or earth. This is not usually a problem with modern wiring codes in either country, but older American amplifiers have two-prong plugs that are not necessarily polarized for what we call the "hot" (black mains wiring) and "neutral" (white mains wiring), and they can be reversed, sending the voltage to the chassis making a touch-shock hazard. Modern amplifer plugs have a three prong plug, which the third plug is green for direct to earth and is usually bolted by a lug onto the chassis, so if anything happens internally to the amplifier, it is earthed or grounded directly. I have an older Fender Bassman Export head of the same model that Macca used on the Beatles Apple Corp. Saville Row rooftop concert, which I have had to have the mains rewired for a modern three prong plug to address this issue.

Unfortunaltely, in spite of safety, the three-prong scheme does cause its own problems with audio equipment with possible ground or earth loops that can induce hum and noise. But it is a small price to pay for the added safety of the third prong direct to earth. Here in the USA, I have a rack mounted tuner that I use a three-to-two prong adaptor on its plug so that ground or earth loop noise is eliminated. It is not a hazard, because it is eventually grounded to the chassis anyway through the daisy chain between the instrument and the amplifier.

Now, all the above is compounded by the UK scheme which is just as complicated, if not more so. Worse, the colours of the wires are different, so a do-it-yourself-er cannot simply rewire point-to-point. Even if there is a universal mains transformer in the amplifier, as with many Marshall amplifiers, including my 1975 2203, so that all that needs to be done is change the primary mains tap, the correct colours and configuration of the mains wiring must be attended to with the proper plug wiring to make it work. And it must be "Good British plugs" at that.

Some newer amplifiers, like my Carvin MB12, have automatic voltage sensing input circuitry, so it is not the issue it used to be, but on older amplifiers, it can mean the difference between working properly and electrocuting something or someone.

I don't necessarily like Wiki, but it can provide a good starting point for more in-depth discussion and resource links, so with that in mind, compare USA wiring:
[url="http://en.wikipedia.org/wiki/Electrical_wiring_in_North_America"]http://en.wikipedia....n_North_America[/url]
to UK wiring:
[url="http://en.wikipedia.org/wiki/Electrical_wiring_in_the_United_Kingdom"]http://en.wikipedia...._United_Kingdom[/url]
Because, we must have "Up, Up Up!" with the voltage, with "Good British Plugs," because
Algernon: "It's green there in America."
[but]
Macca: "In some places, it's brown, you know...."
[media]http://www.youtube.com/watch?v=uOkjQjkEjzo[/media]

Edited August 27, 2013 by iiipopes

[BILL POSTERS]

[quote][/quote]

[quote name='iiipopes' timestamp='1377622194' post='2189550']
Grounding and earthing issues. Old American amplifiers can have the white or neutral side of the mains plug wired across the amplifier chassis, dually functioning as the ground or earth. This is not usually a problem with modern wiring codes in either country, but older American amplifiers have two-prong plugs that are not necessarily polarized for what we call the "hot" (black mains wiring) and "neutral" (white mains wiring), and they can be reversed, sending the voltage to the chassis making a touch-shock hazard. Modern amplifer plugs have a three prong plug, which the third plug is green for direct to earth and is usually bolted by a lug onto the chassis, so if anything happens internally to the amplifier, it is earthed or grounded directly. I have an older Fender Bassman Export head of the same model that Macca used on the Beatles Apple Corp. Saville Row rooftop concert, which I have had to have the mains rewired for a modern three prong plug to address this issue.

Unfortunaltely, in spite of safety, the three-prong scheme does cause its own problems with audio equipment with possible ground or earth loops that can induce hum and noise. But it is a small price to pay for the added safety of the third prong direct to earth. Here in the USA, I have a rack mounted tuner that I use a three-to-two prong adaptor on its plug so that ground or earth loop noise is eliminated. It is not a hazard, because it is eventually grounded to the chassis anyway through the daisy chain between the instrument and the amplifier.

Now, all the above is compounded by the UK scheme which is just as complicated, if not more so. Worse, the colours of the wires are different, so a do-it-yourself-er cannot simply rewire point-to-point. Even if there is a universal mains transformer in the amplifier, as with many Marshall amplifiers, including my 1975 2203, so that all that needs to be done is change the primary mains tap, the correct colours and configuration of the mains wiring must be attended to with the proper plug wiring to make it work. And it must be "Good British plugs" at that.

Some newer amplifiers, like my Carvin MB12, have automatic voltage sensing input circuitry, so it is not the issue it used to be, but on older amplifiers, it can mean the difference between working properly and electrocuting something or someone.

I don't necessarily like Wiki, but it can provide a good starting point for more in-depth discussion and resource links, so with that in mind, compare USA wiring:
[url="http://en.wikipedia.org/wiki/Electrical_wiring_in_North_America"]http://en.wikipedia....n_North_America[/url]
to UK wiring:
[url="http://en.wikipedia.org/wiki/Electrical_wiring_in_the_United_Kingdom"]http://en.wikipedia...._United_Kingdom[/url]
Because, we must have "Up, Up Up!" with the voltage, with "Good British Plugs," because
Algernon: "It's green there in America."
[but]
Macca: "In some places, it's brown, you know...."
[media]http://www.youtube.com/watch?v=uOkjQjkEjzo[/media]
[/quote]

Not all transformers are the same. If you use an autotransformer, it could be an issue.

But if you used an isolating transformer, then neither side of the output is connected to the raw mains. So its much safer and just a bit more expensive.

Something like these. But if you shop around you will find much cheaper.

[url="http://www.ebay.co.uk/itm/NEW-Mains-Isolation-Transformer-300VA-230V-PRI-110V-55-0-55V-SEC-CCM300-110-/350846800238?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item51b019516e"]http://www.ebay.co.uk/itm/NEW-Mains-Isolation-Transformer-300VA-230V-PRI-110V-55-0-55V-SEC-CCM300-110-/350846800238?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item51b019516e[/url]

Edited August 28, 2013 by BILL POSTERS

[overales]

@iiipopes the amp is coming with an upgrade to a three prong cord. Already read that this is a nice ugrade that many owners of vintage amps use to do.

Anyway, i keep in mind i'll end upgrading to a dual voltage transformer.

Thanks to everyone for all the info!

[molan]

I have a fairly chunky Maplins step down transformer for mine. It was recommended by Andy Baxter who brings quite a few very nice B15's over.

I've used it in an environment with lots of other electronic equipment around and it's been rock solid and never suffered from any noise.

I know it's a small thing but my B15 is entirely original apart from the valves and I didn't want to start changing things internally

[Mr. Foxen]

You want to more than match the draw of the amp and the rating of the transformer should overrate by a fair chunk as amps draw more when first on (hence slow blow fuses) and can draw varying amounts according to use.

[iiipopes]

[quote name='BILL POSTERS' timestamp='1377702625' post='2190572']
But if you used an isolating transformer, then neither side of the output is connected to the raw mains. So its much safer and just a bit more expensive.[/quote]Not necessarily, especially when using multiple items of equipment in a band setting, due to leakage, inductance, neutral faults, etc.:http://electronics.stackexchange.com/questions/17496/how-is-using-a-transformer-for-isolation-safer-than-just-playing-with-it and [url="http://www.tlc-direct.co.uk/Book/5.8.4.htm"]http://www.tlc-direct.co.uk/Book/5.8.4.htm[/url]