PT transformer known current for heaters wo spec sheet?

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hopkinWFG

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Hi guys just wanna ask if anybody does maths on the known max current a PT would produce for its 6.3V windings for heaters without any spec sheet ? Or rather how would we know the transformers max out current it can provide before we unknowingly design or changed tubes that could potentially damage the PT ?
 
You’d need what’s called an adjustable active impedance load. They’re expensive and not common.

Unfortunately transformers are super efficient - so much so - that what will happen is the secondary HT will reduce in voltage to supply current for the 6.3V winding. Remember that power in is power out - there’s only so many volt-amps allowed from the primary. So as you drive the 6.3V tap harder with more current requirements, the secondary HT will begin to drop significantly to provide the current to the 6.3V tap. This will happen until the insulator for the 6.3V melts or burns and shorts the taps together causing catastrophic failure.

Usually you can look at the gauge of the heater wire and determine roughly the current it’s capable of from AWG standards, but you know nothing of the health of the insulation material around the core if it’s a used PT or an old model.
 
@glpg80 thanks for your great write out... but it seems like manufacturers MM and onetic etc seldom state its maximum current it can churn out... unless we approach to ask manufacturers.... chances are for beginner amp hobbist builders would tend to purchase the wrong or underated PT .... ? Lol
 
hopkinWFG said:
@glpg80 thanks for your great write out... but it seems like manufacturers MM and onetic etc seldom state its maximum current it can churn out... unless we approach to ask manufacturers.... chances are for beginner amp hobbist builders would tend to purchase the wrong or underated PT .... ? Lol
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They state the primary VA. They state to secondary AC. You know the voltage of a heater tap. Theory like this is what differentiates hobbyists from professionals and is why amps are so expensive. We haven’t even gotten into the topic of custom transformers of different core types or designs.
 
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