ok, i'm no expert on transformers, but if i took a transformer that was a 120V primary 48V secondary and wired it backwards, i would get a 120V primary, 300V secondary right? and if i had a 240V primary and a 120V secondary and wired it backwards i would get a 120V primary and 240V secondary, right?
What I've done before is to take two such transformers and wire them back-to-back. e.g. if you have dual primaries then you could do 120:48 -> 48:240 without any fears.
Transformers are typically wound near their limits, so increasing supply voltage even by 120% may cause the transformer to smoke - let alone 200 or 300%!
Putting them back-to-back as Tiroth mentions is a good way of getting around it, but you double the transformer losses and regulation.
Tim
Putting them back-to-back as Tiroth mentions is a good way of getting around it, but you double the transformer losses and regulation.
Tim
well, o hadn't planned on running the transformer to it's limits. i wanted to run a headphone tube amp. the only problem i was having was finding suitable transformers for cheap. i have access to things like 120V - 48V, so i figured i'd use that for the high voltage and use a smaller transformer for the heaters
Backwards arrangement
Hi Chris,
"but if i took a transformer that was a 120V primary 48V secondary and wired it backwards, i would get a 120V primary, 300V secondary right? and if i had a 240V primary and a 120V secondary and wired it backwards i would get a 120V primary and 240V secondary, right?"
Interesting question. Even if you had No load at all, connecting the 48 volt winding to 120 vac will destroy it instantly. The primary inductance won't be nearly high enough.
You are correct on the second example as the 120 vac secondary winding has enough inductance.
Good luck Chris.
Hi Chris,
"but if i took a transformer that was a 120V primary 48V secondary and wired it backwards, i would get a 120V primary, 300V secondary right? and if i had a 240V primary and a 120V secondary and wired it backwards i would get a 120V primary and 240V secondary, right?"
Interesting question. Even if you had No load at all, connecting the 48 volt winding to 120 vac will destroy it instantly. The primary inductance won't be nearly high enough.
You are correct on the second example as the 120 vac secondary winding has enough inductance.
Good luck Chris.
It's not the inductance, it's the saturation. Related but different.
(Someone may argue, well saturation occurs at a certain flux level, which is dependent on current and turns right? Well that inductive current through the winding depends on frequency and voltage.)
Current load has no effect, as current cancels out of the equations.
Tim
(Someone may argue, well saturation occurs at a certain flux level, which is dependent on current and turns right? Well that inductive current through the winding depends on frequency and voltage.)
Current load has no effect, as current cancels out of the equations.
Tim
Even if you could get it to work you cannot change the balance between voltage and current. If you step up the voltage the current will go way down. A transformer is a near perfect thing, most are high 90's when it comes to efficiency percentage. 100 va's in will get you just about 100 va's out. You can't change that.
VA's = E x I
VA's = E x I
> connecting the 48 volt winding to 120 vac will destroy it instantly.
Not quite instantly. Been there, done that. It may take 30-60 seconds to get burning, although with a large transformer you may just blow house-fuses first. An over-volted transformer is much like a short, whether you compute inductance or flux.
They don't give you much leeway on transformer rated voltages: why pay more if you aren't going to use it? A 120V winding fed 130V won't burn-up, or not for a very long time. But a 48V winding fed 120V will saturate, act like a near-short, suck a lot of current, and something will die.
You can do it the other way: put 120V on a 230V winding. The current rating is hardly changed, so you paid for twice as much core as you needed, and the resistance is not as low as a winding optimized for the working voltage, but nothing will blow-up.
Not quite instantly. Been there, done that. It may take 30-60 seconds to get burning, although with a large transformer you may just blow house-fuses first. An over-volted transformer is much like a short, whether you compute inductance or flux.
They don't give you much leeway on transformer rated voltages: why pay more if you aren't going to use it? A 120V winding fed 130V won't burn-up, or not for a very long time. But a 48V winding fed 120V will saturate, act like a near-short, suck a lot of current, and something will die.
You can do it the other way: put 120V on a 230V winding. The current rating is hardly changed, so you paid for twice as much core as you needed, and the resistance is not as low as a winding optimized for the working voltage, but nothing will blow-up.
trannies
You didn't mention if it was a toroid! If so, manufacturers usually wind for 1.6 Teslas i.e limit of Bmax mag sat. Playing about back to front on this type could cause interesting black outs.
I am also a qualified welder. Better to get the right part for the job.
You didn't mention if it was a toroid! If so, manufacturers usually wind for 1.6 Teslas i.e limit of Bmax mag sat. Playing about back to front on this type could cause interesting black outs.
I am also a qualified welder. Better to get the right part for the job.
Are you sure?
Thanks for the correction Schematic.
"(Someone may argue, well saturation occurs at a certain flux level, which is dependent on current and turns right? Well that inductive current through the winding depends on frequency and voltage.)"
Conversely, if the turns were increased, then saturation would't occur for the given standard voltage, 120, and frequency, 60. However, the turns aren't increased and the voltage is as stated.
Used the word "instantly" because I wanted to scare him and make sure he didn't try it. Maybe I shouldn't have done that. Sorry.
Thanks for the correction Schematic.
"(Someone may argue, well saturation occurs at a certain flux level, which is dependent on current and turns right? Well that inductive current through the winding depends on frequency and voltage.)"
Conversely, if the turns were increased, then saturation would't occur for the given standard voltage, 120, and frequency, 60. However, the turns aren't increased and the voltage is as stated.
Used the word "instantly" because I wanted to scare him and make sure he didn't try it. Maybe I shouldn't have done that. Sorry.
Voltage doubling.
Hi Chris,
You could use a voltage doubler or tripler circuit to bring up your supply voltage with the 48 volt winding. With over a 100 volts dc you could possible run your headphone amp - or modify it to run at that voltage.
With 48 volts rectified you can even run a 6DJ8/ECC88 with very good results. A tested circuit is on this forum.
Cheers.
Hi Chris,
You could use a voltage doubler or tripler circuit to bring up your supply voltage with the 48 volt winding. With over a 100 volts dc you could possible run your headphone amp - or modify it to run at that voltage.
With 48 volts rectified you can even run a 6DJ8/ECC88 with very good results. A tested circuit is on this forum.
Cheers.
backwards tranformers
Yes positron, the scare is no bad thing, in reminding the abilities of others of using AC mains voltages without proper bench discipline. Over here with 230V I am pretty strict about this philosophy.
The doubler solution is far more viable, only to say that I often found it causing modulation hum in valve circuits. You might have to bypass each rectifier with a 10n or higher value cap.
As for specs, a rule of thumb for those without audio test rigs, amplifier noise is pretty faint in headphones around -75dB down (~140uV); (OdBV 600ohms ref 0.775V), and if you are using a rough PSU you will soon hear other unwanted noises too.
The quietest phone line (if one has one) is about -70db down.
Remember, It depends how clean your AC line is. Mine over here is dreadfully noisy.
more.... anon
Yes positron, the scare is no bad thing, in reminding the abilities of others of using AC mains voltages without proper bench discipline. Over here with 230V I am pretty strict about this philosophy.
The doubler solution is far more viable, only to say that I often found it causing modulation hum in valve circuits. You might have to bypass each rectifier with a 10n or higher value cap.
As for specs, a rule of thumb for those without audio test rigs, amplifier noise is pretty faint in headphones around -75dB down (~140uV); (OdBV 600ohms ref 0.775V), and if you are using a rough PSU you will soon hear other unwanted noises too.
The quietest phone line (if one has one) is about -70db down.
Remember, It depends how clean your AC line is. Mine over here is dreadfully noisy.
more.... anon
what about a voltage quadrupler run from a switching circuit to get the switching frequency above 60hz. i mean i guess it'd be noisier, but it would work and not blow up right?
I've done it under certain circumstances. For instance, I needed a bias supply for 6550s. I didn't have the right transformer at hand and the main transformer didn't have a bias tap, so I ran a 10V (I think it was 10, it's been a while) 'backwards' off the heater winding (6.3V) of the main transformer. Perfect.
One thing to note is that bias circuits aren't current hogs, so I was only lightly loading the 'secondary.'
I don't know as I'd go so far as to run the thing up to 300V, though.
Voltage quadrupler from a switching circuit? Why not just run it from the AC line?
Grey
One thing to note is that bias circuits aren't current hogs, so I was only lightly loading the 'secondary.'
I don't know as I'd go so far as to run the thing up to 300V, though.
Voltage quadrupler from a switching circuit? Why not just run it from the AC line?
Grey
doubler, quad rectification
Regulation gets worse with increasing current demand. Quad is generally much worse.
Regulation gets worse with increasing current demand. Quad is generally much worse.
yes, but regulation gets better with increasing capacitance and increaseing frequency. since the idea behind a switching power supply is to get a high switching speed, and because low voltage electrolytics can be pretty big, the regulation shouldn't be too bad, especailly given a low current application.
the transformer also has a 14Vct that i will get my +6.3V (1A) from. the windings are for up to 3amps. also i'd prefer isolation for my circuit.
the transformer also has a 14Vct that i will get my +6.3V (1A) from. the windings are for up to 3amps. also i'd prefer isolation for my circuit.
OPPPPPs
Didn't see the switching supply mentioned earlier. Yes it would, but isn't it getting kinda complex. I mean wouldn't it be simpler to just get the proper tranny?
Just asking. 🙂
ps. Capacitor size could affect fidelity.
Didn't see the switching supply mentioned earlier. Yes it would, but isn't it getting kinda complex. I mean wouldn't it be simpler to just get the proper tranny?
Just asking. 🙂
ps. Capacitor size could affect fidelity.
well yes it'd be easier, but not cheaper. i have most if not all of the parts required just sitting around (sans the tubes and associtae high voltage caps). i have plenty of 50V rated caps that would work fine. basically as i see it the transformer, purchased online would cost me $50 after shipping and all of that! this is way too much. lets be honest, this amp is superfluous -- i already can run my headphones from an existing source. this is spending about $100 to do a function i can already do... that's too much. but if i didn't have to buy a $50 tranformer, i could justify the expense on the extra parts because tubes have novelty value in the order of $20 at least.
so i wanted to build the tube amp from parts i have or at least could reuse if the amp ever got take out of use.
so i wanted to build the tube amp from parts i have or at least could reuse if the amp ever got take out of use.
i noticed a torroid here:
http://www.apexjr.com/miscellaneous.html
Basler 16-16431
120V input Marked at 300 Watt checked out as 500W
Output Dual 52V, Dual 10V, 20V, and 6.3V taps
$25.00ea
it is still prety expensive, but if i order parts for the amp, i may be able to basically get an effective discount -- there is a $25 minimum order, and well, i would otherwise need to buy extra parts. in any case, any opinion on this transformer? i had planned to build the case into a coffee can as coffecans can be made aesthetically plesing with some skill, they are metal, and are usually pretyy structurally sound. my only worry was in placing the tubes directly above the tranformer.
http://www.apexjr.com/miscellaneous.html
Basler 16-16431
120V input Marked at 300 Watt checked out as 500W
Output Dual 52V, Dual 10V, 20V, and 6.3V taps
$25.00ea
it is still prety expensive, but if i order parts for the amp, i may be able to basically get an effective discount -- there is a $25 minimum order, and well, i would otherwise need to buy extra parts. in any case, any opinion on this transformer? i had planned to build the case into a coffee can as coffecans can be made aesthetically plesing with some skill, they are metal, and are usually pretyy structurally sound. my only worry was in placing the tubes directly above the tranformer.
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