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Old 12th March 2008, 06:10 PM   #1
JoshK is offline JoshK  Canada
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Join Date: May 2004
Location: Toronto, ON
Default Filament transformer questions

I have some filament transformers that have me scratching my head some. I got these from These are the (TP) 19-P-33.

The website says they are 1.2a, but I have them and also have a couple others from their website that are rated for higher current. The thing is the 19P33's are much larger than the 2-4a FT's. They are quite heavy and the wiring isn't puny. It would see to me that they might really be rated for more and mis-marked.

How does one test to see how much current a given transformer can deliver? Do you set up different loads for different currents and measure voltage for regulation and call it at a certain spot? I think I've read that the industry rates them for a specific temperature increase.

My second question pertains to how much abuse can a FT take. For example, can you hook up tubes that draw 6.3v @ 2.4A on a 2A FT? What percentage abuse would be fair/not-fair?
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Old 12th March 2008, 06:35 PM   #2
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Join Date: Jun 2002
Location: Macedon NY
Connect a 6AS7 and see how much the voltage drops at 2.5A (I keep one handy with clip leads just for testing transformers). If it drops 0.6V that's 10%. < 10% means that the transformer is dissipating less than 10% of the 15 watts delivered...

Small transformers will have too much voltage drop before they're in danger of overheating. Large ones are limited by heat before voltage drop is a problem.
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