Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on October 31, 2014, 03:11:25 am
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Hi guys, I need a filament transformer and I was hoping to use a transformer I can get from a local store.
It has a 240v single winding primary and 2X15v secondary's.
Can I connect the 15v and the 12v taps together to give me 6V and will this still give me 6A of current. Thanks
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:think1: :think1:
if the 15V is rated at 6A and the 12V is an intake in the same winding 0-12V-15V the wire is the same thickness and can hafford a current of 6A the same is from the 12V intake to the 15V intake
otherway the dissipation is on a shorter winding so dissipation will be less, but you are taking a lower voltage
so 15V*6A = 90VA is the max power you can take of 1/2 of the transformer (0-15V winding)
12V*6A = 72VA is the power you take from 0-12V winding
and 3V*6A = 18VA is the power you take from the 0-3V winding
90VA*2 = 180VA - the total power of the transformer
18VA*2 = 36VA - the power you are using from the transformer without excess the wire ability
I think you are fine and can take all the 6A that the wire diameter give on the 6V total winding formed with the two 3V itakes
EDIT: I've seen your sch file, you say 100VA @ 6A so you have two 15V 3A windings that in parallel will give 6A
15V*6A = 90VA so is impossible that the transformer is OK for this purpose, the 100VA @ 6A sure refers to both 15V winding in parallel
if you use the two 3V intakes (from 12V itake to 15V intake) the max current you can take is 3A (or slightly more)
because of the insufficient tickness of the wire of the winding to support a withdraw of a current that is double respect his ability
Franco
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If your amp has even number of tubes you could connect the 12V secondaries together
and use the 12V for heating of tube pair (heaters connected in series). The maximum current is then
12A if 6A is specified for one secondary.
/Leevi