Filament transformer questions

JoshK · 12th March 2008, 05:10 PM

I have some filament transformers that have me scratching my head some. I got these from surplussales.com. 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?

Tom Bavis · 12th March 2008, 05:35 PM

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.

12th March 2008, 05:10 PM	#1
JoshK diyAudio Member Join Date: May 2004 Location: NJ/NYC	Filament transformer questions I have some filament transformers that have me scratching my head some. I got these from surplussales.com. 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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12th March 2008, 05:35 PM	#2
Tom Bavis diyAudio Member 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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