Transformer Wire Thickness

Discussion in 'Amp Tech Center' started by gabasa, Jul 31, 2020.

  1. gabasa

    gabasa NEW MEMBER!

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    Hey all, if you're building a Champ, what voltage rating would you want to see on the wire leads coming out of the output transformer, as a bare minimum, for safe operation?

    I have an OT that has 300V wires, which I think is technically ok, they just look thin....

    Thanks.
     
  2. Jon Snell

    Jon Snell Tele-Meister

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    Depends on the current load but most wire sold for hand wiring or "hook up" wire is rated with 700volts insulation.
    I use 16/.02mm Equipment wire for most wiring and solid strand 0.75mm for output valve, heavy current heaters with the thinner more manageable 16/0.02mm for pre amp low current heaters.
     
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  3. rangercaster

    rangercaster Poster Extraordinaire

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    I just buy gear instead of building it ...

    A bit more spendy....


    But I get more leisure time ....
     
  4. King Fan

    King Fan Poster Extraordinaire

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    Is it a guitar amp OT that's built for a Champ, or an OT out of something else? Do we know what?

    FWIW, 'thin' is gauge, which affects ampacity, ie current carrying, while 300V is a rating on the insulation. All these things interact, of course, as does wire *length,* which luckily is short here.
     
  5. schmee

    schmee Doctor of Teleocity Silver Supporter

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    For a Champ, tiny wire is OK. Probably 24 gage or smaller even.
     
  6. David Barnett

    David Barnett Doctor of Teleocity

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    Transformers are tested at much higher voltages than anything they'll see in use. Reputable manufacturers will Hipot test every unit before it ships.
     
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  7. Nickfl

    Nickfl Tele-Afflicted

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    Keep in mind that a lot of older amps were built with 300v hookup wire throughout, and the actual failure voltage is much, much higher than that (3000-4000V). The rating on this stuff is very conservative and builds in a huge margin of error for the peace of mind of both engineers and insurance purposes.

    The cloth covered push back wire that a lot of people like never seems to have a voltage rating, probably because it either doesn't have one or it is low enough that it would raise questions.

    As @King Fan said it is an interaction of voltage, current and temperature that define the limitations of the wire. 300v wire is rated to 300v, but practical experience show that is it more than ok to use in guitar amps even at higher voltages.

    I looked into all this a while back when I realized I had used 300v wire on a lot of my builds that had voltages higher than that rating. I found more than a couple of threads on various forums where I was surprised to find EE types reassuring worried amateurs that the voltage rating on this type of wire are so conservative that exceeding them by 50% in a guitar amp was of no consequence. Hoffman also sells 300v rated wire and says it is fine for higher tube amp voltages, if there was any problem with that I think he would have found out by now.
     
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  8. telemnemonics

    telemnemonics Telefied Ad Free Member

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    The wires coming out of the OT connect to the speaker VC, which is wound with pretty thin wire AFAIK?
    There it has not only the potential to fail from current, but also from friction generated heat.
    Not sure how thin the wire is for a given power handling, just asking.

    I tend to look at things and want them to be way to over built.
    For years I made my guitar speaker cables with very heavy fairly expensive stereo speaker cable, hard to solder to the little 1/4" plugs. Now I use cheap brown lamp cord, probably 16awg which is still way heavier than needed.
     
  9. telemnemonics

    telemnemonics Telefied Ad Free Member

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    In reality the system used to rate wire is terrible and IMO does not work.
    Because: length of run.

    When we look at house wire, and try to determine which gauge to use for a given run, AFAIK the rating does not take wire LENGTH into account.
    If you do some research you'll find that the rating stamped on the insulation only applies to short runs, where longer runs of wire for example fail to meet the (commonly 15a) rating.
    Add in the fact that many consumer devices rated at 15a current draw actually draw more than 15a at startup, then calculate something like 100' of house wire rated for 15a @ 120v, the result ends up being the breaker trips when you try to make a cut with your chop saw, despite all your specs being correct.

    So while specs are supposed to have a big margin of safety, all you have to do is replace that 15a breaker with a 20a breaker to stop it from tripping, then unknowingly somebody plugs in a second appliance running off the same safe wiring, and that wire gets smoking hot.
    16awg rated for 15a @ 120v is so far from adequate that going to 14awg isn't even enough, and you really need 12awg if you might run a 15a home device a distance from the breaker panel. That's my grok of it anyhow.

    Still, the 300v rated insulation does the job and doesn't melt.
    While the wire is smoking hot.

    Doesn't apply to the Champ OT but worth considering.
     
  10. Jon Snell

    Jon Snell Tele-Meister

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    Copper has a conduction and is rated at 1 square in of copper passes 1000amps.
    Insulation is totally different.
    A 15A cable requires a 1.5mm cable. Length does come into it but we are talking about an amplifier with a maximum run of 18 inches.
    telemonics, please don't confuse the readers.
     
  11. telemnemonics

    telemnemonics Telefied Ad Free Member

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    That's fair, but it speaks to the question: what does rated for 300v mean?
    We still have to learn more than it takes to cut a wire and solder it in!
     
  12. Nickfl

    Nickfl Tele-Afflicted

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    What it really means is probably something that should be answered by an electrical engineer, but for what it's worth heres a screenshot of the data sheet for 22 gauge 300 volt hook up wire from Tayda that I have used on a number of builds.

    Screenshot_20200801-152755.jpg


    It's rated for 300 volts at 80 degrees C and tested at 2000 volts for 1 minute. It's also spark tested at 4,000 volts, my understanding is that is a production line quality control test to ensure that there is not any flaw in the insulation sheath. Take those numbers with a grain of salt they're obviously not something the wire could reliably stand up to in everyday operation but they show this wire can stand up to much larger voltages under limited circumstances.

    I seem to remember reading somewhere that the rated voltage on a wire is supposed to be some specific fraction of its failure voltage with a 50% margin of error. So double the rating then multiply by x and that's the voltage at which the wire becomes statistically unreliable. I don't remember what that X factor is supposed to have been though, and of course there's a whole set of specific conditions for determining what that voltage at which the wire becomes prone to failure would be as well.

    Anyway, everything I've read seems to confirm that pushing a wire 50% or so beyond its rating for voltage in a guitar amplifier is not going to cause a problem. A lot of people would refuse to use anything less than 600 volt rated wire which is fair enough, but the 300 seems to be fine as well.
     
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  13. gabasa

    gabasa NEW MEMBER!

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    Wow, this is great info, thanks so much.

    This is a version of Hammond's 1760C output transformer called the 1760CP. They've made this series for years without issue, it was just surprising to see something that looks as thin as guitar pedal hookup wire. Hammond knows what they're doing.
     
  14. Jon Snell

    Jon Snell Tele-Meister

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    Rated at 300volts refers to the insulation, not the conductor. Hipot testing is a non destructive procedure for transformers where the insulation breakdown between primary and secondary is rated. Mostly at 1,500volts in the UK to ensure a doubly insulated transformer is safe to use without an earth bonding.
    Screenshot 2020-08-02 at 08.59.34.png
    This is the sort of information I had to learn upon passing my 17th Edition Electrical Engineering Exams. (Dead boring stuff but has to be known).
    Hope that answers your question.
     
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  15. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Well this is info that a guitar player really doesn't need, but an amp builder might want to at least be aware of, if not fully understand!

    My thinking anyhow, when I learn that I don't know something, is that I like to get a more thorough answer than "go" or "no-go".

    Transformers are a bit like pickups in that AFAIK a current is induced in the secondary by magnetism, since there is no electrical connection to the primary. So the wire in the secondary is really pretty thin, not as thin as pickup windings, but the secondary that has to "pick up" the magnetic power induced in the laminations by the primary winding, is way thinner than the primary winding?

    Is that vaguely correct?
    Looking at for example Partridge transformers where we can see the secondary winding connecting to the hookup wire, I believe the hookup wire is thicker than the secondary winding, and we can see then that the secondary is really pretty thin.
    While the OP asked about the secondary hookup wire? Not the secondary winding wire?
    AFAIK secondaries run like 70v?
    Not sure what the primary winding carries for voltage or current but it must carry more current than the secondary winding?

    (of less significance here but still electrically factual, is that 300v at high amperage will likely melt that 300v insulation, and high enough amperage would even melt the wire! No? In fact a much lower voltage would melt that 300v insulation and the core wire, with high enough amperage? Amperage not present in a Champ, but possibly present in other civilian electrical things an OP might apply their TDPRI derived EE knowledge to!)

    My point is that often it's good to "confuse" an OP when they ask an amp building question, because there just might be members like you who really know this stuff, where us hobbyist amp techs and builders sort of paint by numbers, often without ever understanding what we're working on at an EE level.
    Understanding isn't required now like it used to be, but it's good!
     
  16. Jon Snell

    Jon Snell Tele-Meister

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    telemnemonics ... almost.
    The secondary hook up wire has two requirements; current and voltage. The current on a high voltage winding is normally milliamps so copper area is immaterial but insulation is the main query. If it is to be used at high temperatures >100℃, then silicon or PTFE insulation must be used. All wire manufacturers rate the working voltage with rated temperature. As transformers will suffer themselves with temperatures of over say 70℃, most plastic insulation is absolutely fine.
    A pickup is a coil around a permanent magnet and when a steel (magnetic) string moves within the magnetic field, it induces a voltage in the pickup coil and is amplified to make a similar thing with a speech coil and the air is moved with a cone.
    A transformer however uses a permalloy core, this is an iron core than can be magnetised and lose its magnetism quickly. The weight of the primary winding must always equal the total weight of the secondary/ies to be as efficient as possible.
    If the design requires more secondary current the gauge of enamelled copper wire is increased at a cost of voltage, so to increase the voltage and size requires a larger core area and therefore more weight on both sides of the windings.
    The theory goes very deep as the frequency increases to and beyond the point that rule of thumb, the higher the frequency, the less iron (to become ferrite), is required; SMPSus use heavy gauge windings but little ferrite cores for that reason.
    50/60HZ transformers require a lot more 'iron' than 250kHZ transformers.
    Sometime I read of DIYers adding extra windings to transformers to gain more voltage but we never seen to read of any success for some reason.
    Hope that makes sense as being dyslexic, I have trouble in explaining thing.
     
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