I have not, I'm still going to add a primary as I read on another site that a "plug" fuse is not enough and that a primary is mandatory I just don't want this thread to turn into an argument of different points.
I'm also starting to understand now about how wire size needs to be able to able to withstand or exceed fuse size. I have to look into that a bit more.
I think I will go for a primary fuse only at 1.5*30(VA)/230V which is 0.19 fuse size. I'm going to pick up a 0.2A (well a few of them) from eBay as I think this will be adequate.
No need for a secondary as its optional, and unnecessary I think. My tube buffer with transformer resembles closely what has been posted by AJT's pics.
Wire will be thick enough before and after the fuse.
I'm also starting to understand now about how wire size needs to be able to able to withstand or exceed fuse size. I have to look into that a bit more.
I think I will go for a primary fuse only at 1.5*30(VA)/230V which is 0.19 fuse size. I'm going to pick up a 0.2A (well a few of them) from eBay as I think this will be adequate.
No need for a secondary as its optional, and unnecessary I think. My tube buffer with transformer resembles closely what has been posted by AJT's pics.
Wire will be thick enough before and after the fuse.
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Just in case i decide to go for the secondary fuse, is the calculation below correct for 230V/12V transformer ?
Difference in ratio for primary and secondary voltage = 1:19 (230/12)
Primary to secondary 100% efficiency equals - 0.2A (as calculated in the post above) * times 19 which would be 3.8A (a 3.8A fuse for the secondary).
Given a more realistic figure of 80% efficiency from primary to secondary the figure would be 3.04.
So given the calculations I could use a 0.2A fuse in the primary, and a 3A fuse in the secondary.
Am I correct?
Difference in ratio for primary and secondary voltage = 1:19 (230/12)
Primary to secondary 100% efficiency equals - 0.2A (as calculated in the post above) * times 19 which would be 3.8A (a 3.8A fuse for the secondary).
Given a more realistic figure of 80% efficiency from primary to secondary the figure would be 3.04.
So given the calculations I could use a 0.2A fuse in the primary, and a 3A fuse in the secondary.
Am I correct?
I think that transformers are VA rated for the output. If so, then any efficiency correction would increase the operational primary current.
A 200VA 12+12Vac transformer has a maximum continuous AC current output of 200/{12+12} = 8.33Aac per 12Vac winding
A 30VA 9+9Vac would be 30/{9+9} = 1.67Aac
But the load provided by typical amplifiers is not constant and very impulsive.
The 8.33Aac winding could see a continuous 0.03Adc and a stream of low duty variable pulses exceeding 15Apk while operating but different again during start up.
Charging the main smoothing capacitors from zero volts can see peaks that exceed 100Apk
A 200VA 12+12Vac transformer has a maximum continuous AC current output of 200/{12+12} = 8.33Aac per 12Vac winding
A 30VA 9+9Vac would be 30/{9+9} = 1.67Aac
But the load provided by typical amplifiers is not constant and very impulsive.
The 8.33Aac winding could see a continuous 0.03Adc and a stream of low duty variable pulses exceeding 15Apk while operating but different again during start up.
Charging the main smoothing capacitors from zero volts can see peaks that exceed 100Apk
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What would you recommend for the secondary based on the 0.2A for the primary? I think AJT recommended 2A but am wondering how he came to that conclusion and if it was based on a primary fuse which I have read that secondary fuses ratings are based upon. (just for future uses so I know this stuff).
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