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Old 21st July 2013, 03:52 AM   #1
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Default 2 amp simulation/dummy load for transformer

I've got a 30VA rated transformer for a 12.6v filament circuit and need about 1.7 amps, is anyone able to inform me how best to set up a test circuit to ensure the 12.6v (post rectification) won't drop below the 10% allowable for tube filaments? 30va should give 2.4 amps (using a low voltage drop regulator etc)....
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Old 21st July 2013, 04:37 AM   #2
BZed is offline BZed  United States
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What's wrong with a 7.5 ohm 50 watt Dale or ohmite resistor?
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Old 22nd July 2013, 04:08 PM   #3
DF96 is offline DF96  England
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Rectifying and smoothing a transformer output immediately means that you get significantly less DC watts than the VA rating, especially for constant load duty like a heater circuit. I don't carry the exact figures in my head, but assume a 30VA transformer will provide about 10-15W of constant DC.
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Old 22nd July 2013, 04:13 PM   #4
tomchr is offline tomchr  United States
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You can set it up in spice or PSUD II. Have a look at the RMS current in the secondary for a given load. I suspect that under the conditions you mention, you'll exceed the transformer rating of 2.4 A.

~Tom
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