Help figuring out unknown transformer - Page 1
Forum section: electronics / projects

author: cmndr brain
author_rank: Newbie
timestamp: January 19, 2024, 03:35:39 am
content: I am trying to help a friend identify an unknown transformer. (Mainly because he has 62 of them) I am inexperienced when it comes to analog electronics.I've done quite a bit of research, using suggestions on this blog and others.First, I'm not exactly sure what type of transformer it is. Power, audio, output... Personally I believe it's a tube amp power transformer. The only markings on it are a stamp of "A6117"Second, I can not verify what is input or output.The transformer has 11 wires and I've ohm'd out all the leads and to verify what's related and have found 4 sets of windings. 3 of which have center taps.I then put a LCR meter to each and found the inductance of each. I'm not sure if this was correct or not, but helped me make a decision on what might be the input.I decided that the Black and White/Black wires were the input. This is a c.t. winding but the Red/Black wire was so close to the reading of the White/Black, I figured it was a 120v/110v selection.Next, I applied a signal generator and found the relations between the windings.Finally, I used a variac, with a 75watt bulb in series, to take readings at increasing voltage levels.If my guess on the input windings was correct, the outputs "seem" to coincide with what might be a tube amp power transformer.I've come to this conclusion because there was a 6.2v output and a 179v which might be a tube heater and B+ voltage?There is not a typical 5v. Instead there is a c.t. 63v winding that is equal on each side of the center tap (31.5v & 31.6v)Can anyone tell me if my methods were/are correct and whether or not I've correctly identified this transformer. If not, what should be my next step?Thank you.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 19, 2024, 03:44:20 am
content: Can you put it on a set of kitchen scales and weigh it?With all those windings I'm also guessing a vacuum tube transformer. B+, filament, possible screen voltage as well for tetrodes/pentodes.

author: jonpaul
author_rank: Super Contributor
timestamp: January 19, 2024, 10:49:51 am
content: Vacuum tube mains transformer , ~ 50..150W audio amplifier.WDG: 115/125 tapped PRI6.3V FIL170V Plate/B+65V bias, etc.Jon

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 19, 2024, 11:48:30 am
content: Variac with an incandescent bulb is a quite robust way of testing. You can slowly turn up the variac output and note the current increase (maybe add some light resistive loads), At some point you will find that the input current increases significantly more then the output current. At that point the transformer is getting into saturation and you have found the maximum voltage the transformer can handle. The transformer will also start heating up. It has quite a lot of mass, so that takes some time to get hot, but do not do this test for too long, nor drive it too far into saturation.

author: cmndr brain
author_rank: Newbie
timestamp: January 20, 2024, 02:10:42 am
content: Quote from: Andy Chee on January 19, 2024, 03:44:20 amI weighed the transformer on a postal scale and it weighs in a about 6 lbs. A pretty hefty unit.Quote from: Doctorandus_P on January 19, 2024, 11:48:30 amI did have some 47k resistors on the outputs when I took my readings. If I get a chance, I will try to get current readings like you suggest. What restive load would you recommend for that test?Quote from: jonpaul on January 19, 2024, 10:49:51 amjonpaul, thank you for adding some verification to my suspicion.