Help Identifying Transformers

[knotscott]

Hi all - I've acquired a handful of miscellaneous transformers, most of which have no information about them other than the numbering on them.  I'm fairly sure that a couple of them are power transformers, and assume I can measure the secondaries by hooking up the primaries.  Is there anyway to identify which of the bunch are output transformers, and if so, is there a way to determine what the output wattage would be? 

Does this look like an OT?




TIA!

[stingray_65]

Hi Knot,

First thing we need to do is to check your resistance for each tap.

make a grid in a sheet of paper and label across the top Black,Blue,Yellow,Orange,Orange, and Brown.
Label the side of the grid the same way.
put a mark on one of the orange leads so you can differentiate them,

set your ohm meter to the lowest setting and attach to a wire, like the black lead.

test for resistance between every other lead and mark it on your chart.

Also check each lead to the case to see if it is shorted or maybe internally grounded.

each lead should have at least a mate if not two.

once you have this info we MAY be able to help you identify what type of transformer you have.

Transformers generally have a color coded lead arrangement. the one pictured dopes not look familiar at all.

Ray

[knotscott]

Thanks for the quick reply Ray.  I will try to get that info together a little later in the week.  Unfortunately, I'm working 12 hour night shifts until Tuesday, and will see what's left of the brain functions then!  :confused2:

Does this one look familiar at all?

[eleventeen]

You probably have a bit of a challenge on your hands. Stingray has given you a good procedure to log the results of your "experiments".

My experience says with confidence this is a transformer from a Japanese-mfd item. Why? Square corners on the mounting tabs, elongated mounting holes *which favor/suggest small hardware*. If you have taken apart Japanese gear to any extent you'll find they like to use as much same-sized hardware as possible. US gear, sure, primarily 4-40, 6-32, 8-32, but there's no hesitancy using 8-32 on a tranny and 6-32 on tube sockets, for example. Japanese gear, they like to use the same size thread for "everything". Finally, very "boxy" square-corner end bells. It being Japanese or not is neither here nor there, but it *does* relate to the possibility of having a 100 VAC primary winding which is something you have to consider as you suss out what you have.

In the first place, overwhelming all considerations and before you start testing and ohming out...do you have any reason to believe this is a tranny for a tube-based piece of gear? Uhhh, that's kind of critical. The fact of the matter is that the odds favor this being a 36-40, 50 volt secondary from a piece of transistor gear that will find little or no use in a tube amp.

***************

Early Japanese transformers do not use any kind of consistent color code that I am familiar with.

In addition, many Japanese power trannys can run from 100 volts, 120 volts, and 220 volts. This complicates the investigative process, in that we expect to see power trannys with perhaps a 120 VAC winding and a 240 VAC winding, so cool, we'll see three wires that connect together as tested by our ohmmeter. And further, we'll see one of them is a center tap between the other two. Still could be either a power trans or a tube output trans or even a SS out trans, but we like to see that CT winding structure. The 100 VAC winding really throws this line of reasoning off. 

So that is some transformer psychology. Ohms tests are delightful in terms of figuring out what windings connect to what, but they can also be deceiving in subtle ways. They are nevertheless unequivocably the first thing you do. With a transformer like this, lacking a coherent color code, you have to move on to actual live voltage measurements.

The next thing I myself do requires a 6 volt (or "low" volt) transformer, which can be a known filament winding from another transformer, or the output of a variac. Basically, I connect the 6 VAC power source to known complete windings and measure other windings. Need alligator clips and colored tape is very handy. I really like having the stripped-off jacketing from coax cable during this operation, because I can slide the tubing over the stripped end of a wire and be out of harm's way. Slow and methodical is the idea here.

You have to keep your wits about you, because some meters, even good ones, when measuring AC, will give false readings. It's also possible to get a reading, sometimes a pretty high one, across two non-connected windings (meaning...2 wires that do not connect to the same winding.) It's also possible, if you're not careful, to get a genuinely many-hundred volt output if you were to connect your 6 volts across a winding that isn't the right one. Can't happen? Suppose you have a tranny with a 2.5 volt filament winding and a 1200 VAC B+ winding. Connect 6 volts to the 2.5 winding and you'll have over 2500 volts on the B+ winding and 250-260 volts on the primary. Better insulate those, eh?

Also...if you use an older analog VOM you'll get a SERIOUS voltage spike out of HV output taps when you DISconnect the probe leads. Not dangerous, but it can definitely zap you pretty good if you're just casually/carelessly holding wires in your fingers.

Anyway, the point is, a 6 volt source is 1/20th of 120 VAC. Using a 6 volt source will thus drive all the outputs to 1/20th of their operating voltage....uhhhh....assuming you've correctly discerned the primary.

If "nothing makes sense" out of the windings, IOW, they do not form coherent B+ windings and heater windings, then you  probably have an output tranny. And what that could be is a crapshoot.

[eleventeen]

You can definitely see the differences I pointed out between the Japanese tranny and the domestically made one. Round mounting holes, fairly big diameter.

You asked about wattage. There are arcane ways to measure this, but most would just estimate based on size based on experience. Your black metal-cased one is probably 25 watts or so, the open frame one is a tad less, maybe 15-20 watts,

[eleventeen]

This article may be useful.

http://www.radioremembered.org/xfmr.htm

[for power trans]

http://www.radioremembered.org/outimp.htm

[for output trans]

[knotscott]

Eleventeen - Thanks for all the great info.  It'll probably take me a few reads to digest it all.  I hadn't given any thought to whether or not these are from tube or transistor gear, and I have no reason to believe that they're one or the other.....just wishful thinking I guess.  One of the motivating factors about finding out what these are was to save a few bucks on parts for the amp, but if it's going to be a bunch of work invested in a crap shoot, it's really false economy. 

You guys have been great...neophytes like me just don't have places to glean info like this.  While I've got your ear, can anyone tell me what the gizmo is?  It's by GE and has a standard 2-prong plug, a 2-prong receptacle built into the side, and a numbered variable selector switch on the other side.  The numbers on the plate start with something like F2283 C/6 (as interpreted by my wife over the phone), and include CR 9503-207E below that.

[knotscott]

But wait...there's more!  (just when you thought it was safe to look!)

This one might be easier because it's newer and clearly labeled.



This one's an older Philco 32-8248 (352844).  Looks like a PT to me:



I'm a little puzzled by this one...another Philco, 32-7057 (I-35 or 1-35):

[bigsbybender]

The one that's clearly labeled appears to be a transformer for a 25v audio system. Bogen 25v amp  Rauland or Atlas speakers delivering all of the elevator music and notifications of clearance sales in aisle 7 that you can handle!   

25v and 70v systems are popular for sending long audio runs with skinny wire.... then that transformer steps the voltage down and matches the impedance to whatever speaker you have.


I'm 99% sure the Philco is a PT..   I couldn't tell you which are the primaries. It's a fair assumption the Red it Hi-Tension, and the yellow would heat a 5 Volt rectifier.

The potted unit (with the lugs) I also suspect is a PT, albeit probably not very useful for tube work. The pair of lugs are likely primaries and the triplet may be secondaries with center tap.       

[knotscott]

Thanks Bender. Sounds like those little guys are useless too...do any of these coils have value as a large inductor for something like a subwoofer?

[RicharD]

Here's what I do when I have an unknown transformer:

1.  Diagram the transformer on paper noting wire colors and DC resistance.
2.  Break out ye ole lamp limiter and a known good PT with something along the lines of a 5V secondary.
3.  Attach the known transformer to the lamp limiter.
4.  Attach the suspected primary of the unknown transformer to the secondary of the known transformer.
5.  Fire it up and measure Vout / Vin.  This gives you your turns ratio.

Now you should have a decent clue as to what the transformer is.  The lamp limiter is there so if the unknown transformer is shorted, nothing bad happens.  The known step down transformer is there so if you (example typical tube amp PT) connect the source AC to say the filaments, you will get reading a of about 115V on 1 set of wires (actually the line primary) and a normal HT reading vs well over a kilovolt if you plug a filament tap straight into a wall..... which I have done, and it's kinda scary.

Once you are certain which set of windings are which, go ahead and plug the PT into the lamp limiter.  Since there is no load, your voltages should be accurate.  Document your voltages.  Now that you know your DC resistances and secondary voltages, you can use PSU Designer 2 to estimate the transformer's current capabilities.

If you have an output transformer, the reflected primary impedance is "turns ratio squared times the load impedance".  Guestimating the power capability of an unknown OT is a bit of a gray area for me.  I'm gonna say nothing rather than say something wrong.

Working with unknown transformers comes with a lot of risks.  Testing with a lamp limiter and a step down in front of the unknown transformer reduces initial "fact finding" risks, but once installed in a real world situation, the gremlins might show up.  There may be a reason those transformers were pulled back in the day.  I've seen transformers test peachy with no load but as soon as loaded, they smoke.  I love recycling stuff into killer geetar amps, but sometimes thangs don't go as planned.

-Richard

[knotscott]

More great info Richard.  Thank you for taking the time to explain it and for the pic. 

[eleventeen]

Lessee what you got there.

Incidentally, the second one you posted...the open frame dude with the two reds and two yellows coming off one side...I'd betcha a quarter that one is a common type that has a 125 VAC and a 6.3 VAC secondary....a fairly common style/type/mode used for powering a 3-5-7 tube something of an "accessory" nature where beefy B+ for an audio output isn't needed. Maybe it came from an audio or rf generator. An intercom, a low-end shortwave radio. Not gonna be that useful because even with a voltage doubler you're just not gonna be able to scare up even as much as 300 volts for a Champ (which wants 340 but could prolly work on 300). You can try looking around for an amp that doesn't use big volts for the output tubes...but if I'm right about the type, that lowish voltage will prove to be a hard limit on what can be done with it. Whether you have or don't have a CT on the HV winding will determine what type of rectifier circuit you can build/use. The output voltage from whatever circuit-type you choose is fairly predictable if you know the input voltage.

Your GE is certainly some kind of step-up or step-down deal that let's you run 120 VAC gear from 220/240, or it could let you run 120 from 100 VAC. It could also be a 1:1 tranny that serves the important (although not so much any more) function of isolating the chassis of a piece of gear from the AC line. This would have been something a serviceman used to keep from getting zapped while servicing radios which lacked power trannys and thus the chassis was one side the AC line. It could also be ALL of the above. Not very useful in 2010.

Your LM-25-10 newer one is obviously an output tranny, with those 2-ohm 4-ohm 8-ohm leads. You might be able to scrounge up data on this one. Still don't know if it's tube or transistor, though. Yes, Bigsby has it right, that's a 25 volt or 70 volt tranny...still indeterminate whether tube or transistor. Odds certainly favor solid state, just from how new it is.

The first Philco is almost certainly a power trans, classic color coding. HV red (we really really want to find that HV CT if it's there) 5v fil yel, primary black/black 6.3 VAC blu-blu or grn-grn. That one has possibilities.

Second Philco, prolly an interstage audio tranny. It *could* be a LV power tranny, maybe a 28 VAC CT output. But Philco was more an "appliance" mfr vs "industrial control" mfr and so I'd tend to doubt it's a PT. I could be wrong. Generally not used any more.

Richard makes a great point, that sometimes a tranny will work great under no load and yet fill your shop with smoke under load.  Heh, been there, done that.

[stingray_65]

Thanks Bender. Sounds like those little guys are useless too...do any of these coils have value as a large inductor for something like a subwoofer?

Don't ASSume any of these are useless. You may not have use for some of them, BUT eBay might prove that some one wants them, especially after you identify them.

Once I figured out how to quantify the different taps on magnetics, I have had fun identifying and labeling my old Iron.

Sometimes I see a part in my bins and build an entire amp around it, Might be a speaker or a set of tubes, old iron or even a perf board, never know.

Ray

[eleventeen]

So dude, when you get the technique down, let me know when you're ready for this one....



 

[stingray_65]

Now that's just silly!

It looks like Walt Disney drew a plat of spaghetti while trippin on acid 

[eleventeen]

Hahaha

It's a Tek 585 scope transformer. Fortunately, I knew this when I bought it, and the schematic is easily available on the net. However...the form factor for Tek transformers is usually all-enclosed, and all the wires would normally go to a mondo terminal plate where the terminals would be numbered per the dwg. Not so in this case, and, because the wires usually ARE enclosed & soldered to the terminal plate, there is NO PLACE where the color coding can be found.

However, you can see that the wire pairs enter the central winding at corresponding depths. In fact, all wire pairs do. And there aren't any goofy center taps on ANY winding. This wasn't really all that hard to figure out, though it would have been w/o the dwg. It took about 15 minutes to strip the ends of the wires, though, because they are double insulated with asbestos-weave on the inside, and of course I had to scrape off the formvar lacquer to make contact.  

It has 8 (yes....eight!) 6.3 VAC windings. (16 wires)

It has a 15 V winding for a regulated heater supply and a 37 VAC winding for a fan (prob temp controlled) (4 wires)

It has 5 "B+" windings 110-150 volts each, some of which (when wired in the original scope...not here) are in series, some voltage doubled. (10 wires)

And of course a dual 120/240 primary (4 wires)

34 wires. No big deal, just another episode of "Married to my Workbench" from the "Time? What's That?" series of inspirational videos  

[knotscott]

I can't even identify that many colors, let alone voltages in the wires! 

[PRR]

> Philco, 32-7057

That is probably an interstage transformer, single plate to push-pull grids. See if the 3-pin side has DCR over 1K. (If you use a digital meter, you may have to short the other winding so inductive kick does not confuse the digital auto-range.)

These come in two types: step-up and step-down. 400Hz at one side and measure the other will tell.

Interstage transformers have been VERY out of fashion since 1940. Which means it may be worth more to some collector/fixer than it is worth in guitar-land.

As Richard says, I would start volt-checking unknown PTs with 6VAC through a 1 ohm resistor (or lamp and 5VAC) onto the assumed 120V primary. All voltages will be 1/20th of assumed design. If you mis-picked the primary, you are probably still safe (but don't put your fingers on things!). If the measured voltages times 20 "make sense", then you may have got it right. Go for 120V through the lamp-limiter.

I wish I'd done that the day I connected a 120V:24V backward. 12VAC onto the 24V side. It was NOT happy.