People did things in the past and got away with it, but if you follow todays UL and CE standards, you can't do it that way anymore. You can certainly build a transformer with extra windings on the primary side for voltage adjustment, but you can't make a connection from the primary side to the secondary side because it would almost certainly violate insulation requirements. If you want to elevate a winding on the secondary side, that's a different problem. Only the transformer manufacturer can say if it's ok if the info isn't already on the datasheet. The winding in question might have a wrap of insulation sufficient to the purpose, isolating it from the rest, or it might not.
wow leave to work for the week and look at you guys go! 
after reading I've formulated some questions in laymans term.
So what's leathal about doing this? I'm not going to be putting B+ in my mouth for startup. Wouldn't the transformer just melt and/or short out?
If the B+ on this transformer is putting out 950V-1050V would you also assume then that the other secondary which puts out 20V be properly gaurded against arching/shorting if 120V was put through? Also there's two 5V and a 10V lead.
Sorry I can't seem to get specs form the dealer, and a picture of it probably wouldn't help, but I can tell you there's no visiable voltage taps for the primary leads if that helps. Most of the other stuff you guys where talking about is still over my head for now, but I'll be looking it up and studying it in the near future.
after reading I've formulated some questions in laymans term.
So what's leathal about doing this? I'm not going to be putting B+ in my mouth for startup. Wouldn't the transformer just melt and/or short out?
If the B+ on this transformer is putting out 950V-1050V would you also assume then that the other secondary which puts out 20V be properly gaurded against arching/shorting if 120V was put through? Also there's two 5V and a 10V lead.
Sorry I can't seem to get specs form the dealer, and a picture of it probably wouldn't help, but I can tell you there's no visiable voltage taps for the primary leads if that helps. Most of the other stuff you guys where talking about is still over my head for now, but I'll be looking it up and studying it in the near future.
your best option is to get a variac so you can adjust your primary voltage and find out which primary voltage your secondaries will be right if that is what you want...then you will know how many volts off you are with your primary.......you can then order the correct transformer to suit your needs...
if there are uncommitted secondary windings you can measure that too and take note of the voltages.....but check first with the vendor if putting that winding in series with your primary will not have insulation issues....unless the vendor can confirm i wouldn't risk it.....
otoh, if your secondary voltages are high to your liking, it is still possible to make it work and get the correct voltage by using resistors in series with the windings, this is not very efficient thing to do but doable and not put you health at risk....
working with high voltages is very risky....safety first...
btw, working with tubes, you will find that B+ voltages vary widely from no load to full load, a 100volt difference is not unheard off....and if you are doing classA, it is a simple matter of putting resistors to lose voltage since once set, this voltage will not vary anymore, unlike with classAB...
if there are uncommitted secondary windings you can measure that too and take note of the voltages.....but check first with the vendor if putting that winding in series with your primary will not have insulation issues....unless the vendor can confirm i wouldn't risk it.....
otoh, if your secondary voltages are high to your liking, it is still possible to make it work and get the correct voltage by using resistors in series with the windings, this is not very efficient thing to do but doable and not put you health at risk....
working with high voltages is very risky....safety first...
btw, working with tubes, you will find that B+ voltages vary widely from no load to full load, a 100volt difference is not unheard off....and if you are doing classA, it is a simple matter of putting resistors to lose voltage since once set, this voltage will not vary anymore, unlike with classAB...
No. The most likely outcome is having the mains live shorted to the chassis of your equipement, which can lead to this for example:
Guitarists Who Were Electrocuted While Playing [Archive] - Telecaster Guitar Forum
A much safer option is to use a low-voltage, low power transformer as an autotransformer to correct the voltage.
For example, in a 120V systeme system, if you want a 10% correction you would use a 12V transformer rated at 1/10th of the power of the main transformer.
By using a multiple voltage transformer, you can make the correction adjustable by steps.
And since everything in the auxiliary transformer is on the mains sisde, there are no safety issues. At worst, it would blow a fuse.
Whilst I 100 % agree about safety I often use this trick to test a prototype . I know the risks and never offer this to others . I use it to boost a variac sometimes . 270V falls short of the 300 V I prefer when possible .
Other advice is don't leave it unsupervised . Fire risks are far more real .
I do think the valve amps I play with are more dangerous .
A secondhand PAT tester is very useful ( UK testing standard ) . Get certificated and go earn some money .
Other advice is don't leave it unsupervised . Fire risks are far more real .
I do think the valve amps I play with are more dangerous .
A secondhand PAT tester is very useful ( UK testing standard ) . Get certificated and go earn some money .
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