need help I.D.ing an output transformer PLZ

[dansamp]

I have an output transformer with numbers :
TRA-8-5-1
352445


it has multiple secondary cloth leads
green,yellow, orange(or red), and black
primary are red,blue, brown(black??)

anyone know where I can find the specs for it ???
Thank you so much

Dan.........

[CaseyJones]

It's an Essex. Manufactured by the CHICAGO TRANSFORMER DIV of ESSEX WIRE & CABLE. Cloth leads indicate the "445" part of the code is probably 1st week November 1954.

[dansamp]

Thanks Caseyjones
any idea on the primary impedance ??
I do not have a variac to measure or calculate it

Dan......

[Luthierwnc]

I apply a voltage to the primary and take the reading on the secondaries. Divide the first by the second to get the turns ratio. Square that number to get the impedance ratio. Then you know for every ohm on either end what the other side will be.

Example: You put 120 Vac on the blacks and measure 4 on the secondary. 4 into 120 is 30 for the turns. 30 X 30 is 900 for the impedance. An 8 ohm impedance is looking for 8 X 900 or 7.2k on the primary -- in the range for 6V6's, El84's or 7591's. You could work the calculation the other way saying; I have a pair of EL34's at around 3.5k, what will they drive? Divide that by 900 and you get 3.89 -- maybe a pair of 8 ohm drivers in parallel.

Not having a variac makes this a little touchy when you don't know if the trannie works. You have wire nuts on the leads primaries with secondaries splayed around trying to get readings on hanging wires. Don't do this in the bathtub. Plus you need to get a fairly precise reading on the primary. Mine is usually around 122VAC but it can get squirrely. Maybe someone else could chime in if the losses would be acceptable using a 9 volt battery. With a good enough volt meter you can still get the ratio.

Good luck, Skip

[Wayne]

Maybe someone else could chime in if the losses would be acceptable using a 9 volt battery. With a good enough volt meter you can still get the ratio.

You mean a battery that puts out 9 VAC?

If you're unsure whether the transformer is healthy or not, how about putting a current limiting resistor, or maybe a light bulb between the wall voltage and the primary? Still, if you measure the voltage across the primary (which will be less than 120V if much current flows) and the voltage across the secondary, you can divide and get a ratio.


W

[Phil_S]

I'm am hesitant to apply 120v. It's a lot of voltage and it gives me the willies.

You can't do it with a battery. You need a/c across a transformer.

The easiest thing is to find a 1VAC source and apply it to the secondary and see what comes out the primary. No math and the result is the turns. 10VAC is too much for the secondary.

I usually use the 5v winding from a big ol' PT I have on the bench. You need to check the input voltage with the test tranny attached, as the input voltage will sink under load. Then, you guess, based on core size, the appropriate number of watts. If you've got a pair of EL34's or 6L6's, it needs to be fairly beefy, in the 35-50W range. So, it isn't quite enough to just apply the turns ratio and assume the primary:secondary relationship for a given tube.

There must be a way to use the resistance of the winding and the inductance to figure what primary it was intended for. But this is beyond my reach.

[dansamp]

thanks for the input,
I know the OT works I just want to know what the primary Z is and what the secondary taps are
the OT is medium in size but very fat (lots of laminates)
so I am thinking it is probably a Hi-Fi OT

Dan..........

[dansamp]

I just thought of something based on Phil_S 's post
I have a very small filament transformer that is 6 volts at about 1-.5 amps
I will hook that up to the secondaries and can measure across the primaries
can someone help me with the math formula using 6 volts ??

Dan..............

[Phil_S]

The math is very simple. If your input on the secondary is 6.3v and you get 282v on the primary, your turns ratio is 282/6.3 or 45:1.

Take the square of the turns ratio (45*45=~2000). Assume that is the 4 ohm tap. 2000*4=8000 ohm primary.

If this is a hi-fi with typical taps for 4-8-16 ohms, expect turns of perhaps 45:1, 31.5:1, and 22:1 for an 8K primary or maybe 30:1, 21:1, and 15:1 for a 3.5K primary.

[dansamp]

ok for those interested
I hooked up an old Triad filament transformer
it is measuring 8.35 volts (my wall outlet is 122-123v)
so:
filament voltage of 8.35 applied to green lead of my OT = 180.9 v on my primary
fil. v of 8.35 applied to orange lead of OT = 357 v

fil. v of 8.35 applied to yellow lead of OT = 256.7 v

so it looks like I have a primary of approx 3.5 k ohms or 7k depending on the load

green at 16 ohms is 7056 primary
green at 8 ohms is 3528 primary

orange at 4 ohms is 7056 primary
orange at 2 ohms is 3528 primary

yellow at 8 ohms is 7200 primary
yellow at 4 ohms is 3600 primary

does my math look right ??

I am planning to install this into a deluxe reverb for a friend who wants more power and bottom end from his amp and wants to retain the portability of the size of the amp
we have installed a Celestion GH30 and it sounds huge when he plugged his Super Reverb amp through it

I have 6L6 tubes in the Deluxe Reverb and may also install a larger PT as well

for the Purists this is a silverface amp that has been messed with already and he is a full time working musician

thanks

Dan.......

[skyboltone]

I'm am hesitant to apply 120v. It's a lot of voltage and it gives me the willies.

The folks at Heyboer recommend 120 or even 240 across the primary, then take your readings. He says it's just more reliable. Kinda makes sense I guess. Get the iron to a more realistic saturation level. I know that if I do it that way, the final number will usually be a little higher than if I put (say) 10VAC on the 8 ohm secondary tap.

I'm with you though Phil with regard to putting 120 across any secondary tap. Make an unintentional jacobs ladder! Or a smoke bomb. Yikes!

[Luthierwnc]

Dansamp; Your numbers are right on the money.

As to the volts, I don't see a safety difference between blowing 8 volts up to 200 or reducing 120 down to 6. I'd rather have the hotter ones under wire nuts and the low voltage ones exposed. Plus you have the filament trannie that probably isn't UL wired either. A screw-down terminal strip comes in handy here.

I started messing around with amplifiers when there were a lot more mystery tranformers. Tubes had been obsolete for years so you'd keep your eye out at garage sales and flea markets. Now that they have been rediscovered, you have a much better idea what you are getting but paying for the privilege. Certainly there are a lot more guitar winders. If you just need one excellent amp, by all means buy the best. If you make amps for the hell of it (somebody, please stop me), sometimes you try a budget experiment or just make one to use up your spare parts.

For cheap deals now, watch for 1980's clock radios. Most of them have a dozen JRC 4558D chips -- very handy for stompboxes!

Skip