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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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15th Oct 2017, 7:35 pm | #21 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,350
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Re: Murphy A574 Mains transformer getting hot
If I needed to monitor transformer current, I have two different TEK current probes, but I also have a Waugh isolation amplifier, so probes can be connected directly to HV points. The unit has optocouplers inside separating the HV from the scope.
I have frequently used the Ch 1 add to Ch 2 but with Ch 2 inverted on occasions. I also have a little TEK 212 scope, completely isolated and plastic cased. Limited by its 200KHz bandwidth though for some purposes. Les. |
16th Oct 2017, 12:51 am | #22 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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Re: Murphy A574 Mains transformer getting hot
Quote:
Some transformers that were vacuum varnished have the lams very well stuck in the place from new. Recently I was able to un-stack a faulty power transformer in a Tek TM501 power unit, and unwind and push out the faulty primary winding (as it was layer wound with paper and cardboard and not a plastic bobbin) and glue in a new primary winding. It was a very difficult un-stacking due to the excellent varnishing there. |
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16th Oct 2017, 2:02 am | #23 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,711
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Re: Murphy A574 Mains transformer getting hot
This is what I was thinking. ie gaps formed between the "Is" and the "Es". I seem to recall being taught that frame output transformers deliberately have a gap, but I can't recall why, I think they can get hot in operation, perhaps that's a clue?
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16th Oct 2017, 2:39 am | #24 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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Re: Murphy A574 Mains transformer getting hot
Quote:
Class B output transformers don't need the gap because the currents in each half of the primary cancel out the magnetizing effect on the core. (A frame output stage is not dissimilar in overall design to a class A audio output stage) |
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16th Oct 2017, 9:12 am | #25 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: Murphy A574 Mains transformer getting hot
Hi Gents, ref gaps, Argus beat me to it.
Generally speaking there should be an absolute minimum gap in the type of mains transformers we use, difficult if it is a varnished core. Ed |