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 ?
PT transformer known current for heaters wo spec sheet?
- Thread starter hopkinWFG
- Start date
glpg80
Well-known member
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.
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
Well-known member
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.