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Old 2nd April 2005, 12:53 PM   #1
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Default Unknown Toroid Transformer VA

Bought a surplus toroid transformer, labeled:
Definitive Technology
P/N 0072A100
OBJY2 JEC 105
REF# 15-0070
31/96

120v pri/42v ct
secondary voltage when powered 45.3v and 22.81v -0- 22.85v
secondary resistance 1.5 ohms and 1.2 ohms -ct- 1.1 ohms
primary resistance 6.1 ohms

Dimensions are 4.5" wide by 2" high, center hole is 2" wide

I have Dale load resistors, how do I calculate maximum va load?
4- NH-25-19 (25w .01ohm -3+7%)
2- NH-50-31(50w .1ohm 3%)
7- NH-50-25(50w 4ohm 3%)
6- NH-50-25(50w 15ohm 3%)
4- NH-50-121(50w 5Kohm 10%)

Can someone help me calculate primary and seconday fuse sizes?

Thanks Phil
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Old 2nd April 2005, 02:09 PM   #2
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you can probably tell more about the transformer by examining the size (guage) of the wires in the primary and secondary side --

testing the transformer by loading it -- you should measure the heat rise in the core with various loads --

did Definitive use this in one of their speaker amplifiers? -- should give you a clue.
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Old 2nd April 2005, 09:54 PM   #3
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Quote:
Originally posted by jackinnj
you can probably tell more about the transformer by examining the size (guage) of the wires in the primary and secondary side --
Wire gauge, nah, I can't see windings through wrapper.
Unfortunately don't want to damage wrapper to check this.

Quote:
Originally posted by jackinnj
testing the transformer by loading it -- you should measure the heat rise in the core with various loads --
I believe this data on label is spec and temperature- OBJY2 JEC 105. My guess is it's laquer rating is 105F above abient temperature. Maybe someone knows better.


Quote:
Originally posted by jackinnj
did Definitive use this in one of their speaker amplifiers? -- should give you a clue.
Definitive Technology website doesn't seem to have amps.
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Old 2nd April 2005, 10:03 PM   #4
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The rule of thumb of 1 kilo per 100VA gives you somewhere to start.
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Old 2nd April 2005, 10:21 PM   #5
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Quote:
Originally posted by pinkmouse
The rule of thumb of 1 kilo per 100VA gives you somewhere to start.
Sounds like a plan.... Need to take it to work, have shipping weigh it.
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Old 2nd April 2005, 10:24 PM   #6
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Hi,
buy a some scales & then take up cooking for a second hobby.
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Old 2nd April 2005, 10:36 PM   #7
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Quote:
Originally posted by pinkmouse
The rule of thumb of 1 kilo per 100VA gives you somewhere to start.
Is that for Toroids...

The rule of thumb i've seen for EIs is 20VA/lb -- and from a small selection of trafos i have weighed that is pretty accuarate... guess i'll have to go weigh a few known toroids....

dave
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Old 3rd April 2005, 11:18 PM   #8
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after you find out how much it weighs you could compare it to the weights of plitron's toroidal transformers (or another company that has this info. published).

here's plitron's info.
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Old 3rd April 2005, 11:32 PM   #9
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Now there is an idea. By dimension it might be 225va, will have it weighed next.
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Old 4th April 2005, 08:26 AM   #10
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The 2" hole suggests more a 300VA.
I found that manufacturers generally give higher dimension specs than the real, probably like some slack.
Overhere 42vac is a standard size for 300va's , not for 250's, 225's or lower.
A 300 is sized at 4.75" but in reality is 4.5"

Up till 300va 1kg/100va is fairly accurate(+50grams for the smaller of size).
Between 425va and 800va the factor is 0.8 kg/100va.
From 1000va it drops to 0.75 kg/100va and lower.

i did some dimension analysis of toroids long ago(for fun).
The spread then was higher between manufacturers(here).
Copper and steel price for toroid wiring and cores have gone up quite considerable, and competition in the toroid business is pretty steep.
Toroids nowadays are made much more with economics in mind.

But i am very curious if it is a 5.0 or a 6.5 pounder.
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