Step Up Transformer Suggestions?

Discussion in 'Recording Gear and Equipment [BG]' started by DLemos, Oct 14, 2016.


  1. DLemos

    DLemos

    Sep 7, 2015
    I recently got some sweet vintage': A Selmer Bassist Major. It's from the 60's, valve driven, and runs at 220 volts with a British power plug. I was looking at some of step up transformers, and have no idea if any of it's specifications matter with such an amplifier- in this case I would assume the vacuum tubes. The other question I have: Is there an order to turn these two on, I'm assuming the transformer, and then the amplifier?

    Dave
     
  2. tom-g

    tom-g

    Oct 2, 2007
    Do you know how many watts the amp uses? It might tell you on the back. That's what the transformer needs to be able to deliver.
     
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  3. DLemos

    DLemos

    Sep 7, 2015
    Okay, good- something new to me. So the amplifier is rated at 15 Watts, does this mean that the transformer also has to be 15 Watts, or can it be more / less?

    I'm not sure if this helps, but I'm looking at "outboard" transformers, not something I'd like to hardwire into the circuitry, but rather just use it as it's outlet.
     
  4. delta7fred

    delta7fred

    Jul 3, 2007
    England
    A lot of the old British stuff had mains transformers with windings that could be configured for different line voltages. Do you have any photos of the guts?

    If you are going for a step up transformer I would go for one at least twice the amplifier output rating, so 30w or better still 50W.
     
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  5. DLemos

    DLemos

    Sep 7, 2015
    I wish it were that easy, but the plug is still a product of London.

    IMG_1345.JPG
     
    Last edited: Oct 15, 2016
  6. delta7fred

    delta7fred

    Jul 3, 2007
    England
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  7. DLemos

    DLemos

    Sep 7, 2015
    @delta7fred Check my posting in between your last two.

    So I just need a transformer with a serving of at least 15 Watts? Any other specifications?
     
  8. delta7fred

    delta7fred

    Jul 3, 2007
    England
    Sorry for the mix-up, you still need a step up or auto transformer of 30w minimum.

    Something like this - Ebay item 191428487876
     
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  9. DLemos

    DLemos

    Sep 7, 2015
    I forgot! So it's 15 Watts in "U.K.", meaning 30 Watts in "U.S.", correct? Is there any problem with the ones that plug directly into the outlet, with a slot for the plug coming from the amplifier?
     
  10. delta7fred

    delta7fred

    Jul 3, 2007
    England
    The amp has an output of 15W and will have an efficiency of a lot less than that, I guess about 50% but could be less. So half the power it takes is given off as heat meaning that you need to supply it with a transformer having an output capability of 30w minimum. The Mains transformer in your amp will already have a rating in excess of 15w, probably 30 - 50w.

    I don't know of any plug and play transformers in the USA, if you can locate one it will be the ideal solution.

    You might be able to mount a step up transformer in the amp box and fit a standard IEC chassis mounted line inlet socket. Not something to be undertaken if this is your first project using line voltages, especially UK line voltage which as you now know only too well is almost double what you have in the USA. It can give you a nasty jolt (at best) and be lethal if you are unlucky.
     
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  11. DLemos

    DLemos

    Sep 7, 2015
    Sweet! I like to keep my vintage as original as I can, so a "plug and play" is my only option. I'll start looking at some transformers, and see what I can do.
     
  12. DLemos

    DLemos

    Sep 7, 2015
  13. delta7fred

    delta7fred

    Jul 3, 2007
    England
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  14. delta7fred

    delta7fred

    Jul 3, 2007
    England
    It never occurs to me to add a bottle of hot sauce to the order when I am shopping for electronic stuff. :roflmao:
     
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  15. That looks like it will work. You might find a cheaper transformer, but this one is already in a box that you can just plug in.

    15 watts is the audio output power of your amp, but what you need to know is the actual power that the amp uses. Tube amps, especially old ones, are relatively inefficient - a lot of the power that goes in, turns into heat. There should be a plate or a sticker that shows the power requirement. The classic mistake you see is people thinking that number is the audio output power.
     
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  16. wouldn't it be easier or at least cheaper and lighter to just buy a new 110v power transformer for the amp and replace the 220v transformer?
     
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  17. DLemos

    DLemos

    Sep 7, 2015
    Maybe, but I'd rather keep it to it's original specifications.
     
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