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6f6 2nd April 2007 06:49 AM

Unknown Transformer
Hi Guys,
I have an old transformer which was probably used for some 40's vintage radio. It works alright and gives 350-ct-350, 6.3v, and 5v. I would like to use it to power an amp. I know that I can get away with an #80 (or 5y3) rectifier, however I have sitting around a bunch of 5u4 tubes. How would determine if this transformer can take the additional current draw required by the 5u4 tube (type 80 is 5v 2A and 5u4 takes 5v 3A). If anyone has info on old transformers its model numer is JD-104202-B and 5-16-41 (year of manufature?).

Klimon 2nd April 2007 09:52 AM

The natural test is how hot the trafo gets, even more so than a specification on paper. Connect the 5u4g, if the trafo doesn't get warm / stays cool enough to touch within the first minutes the winding is fit for the job. Temporarily overloading a 2A winding with 3A current draw won't destroy it in the first minutes (nor months probably) so this is a safe test....


gingertube 5th April 2007 07:14 AM

What Klimon says.
In general it is the total VA (Volts x Amps) of the transformer draw which can cause overheating. Drawing an extra amp from the 5V secondary winding means that you are presenting a 15VA load instead of a 10VA on that winding. This will most likely not be a problem in (when you consider all of the secondaries) what is probably a 200'ish VA transformer. The extra loading is exactly the same as if you were drawing an extra 7mA from each side of the 350-0-350 High Voltage winding. Most folk would do that without even pausing to think about it.

I've run 5U4 and 5AS4 from 5V 2A secondaries before without a problem and similarly have drawn 10 Amps from a 7A 6.3V heater winding with no problems. Go for it.

If it gets too hot to touch when its in its final circuit with all secondaries loaded you can panic then.


dnsey 5th April 2007 12:52 PM

It wouldn't take long to wire the heaters of your proposed tubes to the txr and check how much droop they produce.

diegot 5th April 2007 06:14 PM

I have a similar transformer at home.
I ran a 5U4 from it without problems, but you can use a 5R4 rectifier, it's like a 5U4 with 5Y3 filament current. A good choice.

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