i have over 15 power trans and all have colors that have faded so its hard to figure out where to hook my 120 volt ac.,, is there a way to test the wires to find out which is the ac lines., thanks

Hi Paul

You can somewhat go by resistance. Filament leads will usually be an ohm or so depending on available current. High voltage windings might be several hundred ohms.

This leaves your AC input wires which can read 20 ohms on an ohm meter. You won't get these exact numbers. It all depends on transformer size & current ratings.

You can depend on filaments being very low. High voltage being the highest resistance. AC input between the two.

Also black are colors for AC if the transformer manufacturer followed the standard.

Norm

:i have over 15 power trans and all have colors that have faded so its hard to figure out where to hook my 120 volt ac.,, is there a way to test the wires to find out which is the ac lines., thanks

After you use Norm’s ratings to figure out which leads should be the 120AC please do not just plug it directly into your house current. Use a variac on the leads you believe are the 120, put your volt meter on any of the others that show they should be filament and apply a few volts to it. Make darn sure the other lines are not touching each other or you for that matter. Simple math will tell you if you’re correct. If you get 10% of the estimated output at 10% of 120v your right on, if your wrong nothing will be fried, including you, and by working with the reading you do get you will eliminate at least one set of leads.

I have seen some schematics in here where 25 volt (and other voltages) tubes are used in series or parallel in a transformer type radio. This is very rare, but if you come across an odd winding, it might be for that purpose. Keep this in mind with oddball transformers that have multiple tap high voltage windings and such, too. I've even seen some Crosleys with taps for series filaments as well as high voltage, all from one winding. Some of these didn't even have a secondary, per say. They just had one winding, which had taps. Part was connected to the AC line, part to the filaments, and probably the entire thing to the H-V. Lots of variations of all that I mentioned above. All are very rare, but are something to watch out for.

T

If you dont have a variac... for safety ..you can easily use a 12v filament transformer to represent 10% of normal AC... and do the math... even a 6v will do.. and adjust your thinking to 5%