# output transformer Math "a little help with ma homework plz"

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#### ArcticBreaze

I hav here for my latest project an old "beacon radio ltd"(old NZ company no longer exists so no data) 7 watt output trany.
hav worked out the secondary side ul taps etc now I never said i was good at math and i may hav cocked this up completely so please check it for me

with 116volts (that's what i had no verible power supply) going into outside winding's of primary i get 4.3 volts on secondary that i think is 8 ohm tap.

116/4.3 = 26.97:1 turns ratio
26.97x26.97 = 737.38:1 impedance ratio
737.38 x 8 ohms =5819 ohms load
or x 16ohms = 11638.08 ohms load

now assuming i got that right its half what i need for my 6sn7

so how do i work out the secondary taps as seen in pic numbered 1-5
measurements were across 1 and 5 with 2and 3 linked this is how it was installed in old an radio so i guessed 8 ohm label says sec 3.75 - 15 ohm primary 9000

plz help it still almost shiny i dont wanna throw it out

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#### VMUNIX

this is what I would do, use a good ohm meter and try to draw a schematic of the secondary winding, first open the jumper between the pins, and then guess by measuring the DC resistance, connect it again to the 116 source and confirm that with the lowest voltage output reading, that's most likely the 3,75 winding and you have to use an 8 ohm speaker there.

#### ArcticBreaze

thanks will try that tomorrow, when i have my good dvm from work and let you know the results

#### ArcticBreaze

ok
secondary Taps 1-2 = 2 volts and taps 3-5 = 2 volts

116/2 = 58:1 turns
58 * 58 = 3364:1 impedance
3364 * 8 ohms is 26912 ohms load right smack in the ball park

now if I run these 2 winding's in parallel what does that do to reflected load ?
or do i just use one of em

#### VMUNIX

ok
secondary Taps 1-2 = 2 volts and taps 3-5 = 2 volts

116/2 = 58:1 turns
58 * 58 = 3364:1 impedance
3364 * 8 ohms is 26912 ohms load right smack in the ball park

now if I run these 2 winding's in parallel what does that do to reflected load ?
or do i just use one of em

No, don't use them in parallel, now the thing is possibly one of those winding is closer to the transformer core and the other is located more in the outside, the one with less resistance should be the internal, I'd use that one, although you can try to other one to see if there's a sonic difference (more treble or more bass response).
Nice transformer perhaps you can open the sides and check where in the bobbin the leads are going. Post pictures.

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