Identify an OT

[dude]

I was given this OT, looks like a PP 10/15 watt, says "EMI 010975"
Was hoping someone could save me some time if they know any specs, secondary..? and impedance..?
Leslie? can't seen to find any thing but pictures.

[shooter]

put in the ac n do the math, 30min later you're out mowing the yard

[Latole]

Look here: for a Leslie

https://shop.smelektronik.ch/pi/Music-instrument-parts/Transformers-Chokes/Leslie-tone-cabinets/Leslie-010975-EMI.html

How I  test and find impedance :

Testing Output Transformer and finding Impedance

1- Signal generator set to 1000 hertz AC 0.5 volts

2- Send this signal to OT secondary , check with accurate meter to have 0.5 VAC on OT tap. Or close

3- Read AC voltage at OT primary

4- For exemple if you read 14.35 VAC you divide by 0.5  ( or what you read at 1- )

    14.35 / 0.5 = 28.7

5- Square the result  ; 28.7 X 28.7 = 829.67

6- Multiply by secondary output impedance where you are connected  , say 8 ohms
    829.69 X 8 = 6631

7 - This reading 6631 is the primary input impedance

If you use two 6L6 in push pull , look on Tube Book for Plate Load resistance . You’ll see you that you need 6000 to 3800 ohms  for two 6L6 in PP class AB

The reading we got 6631 is on spec
_______________________________________
If transformer is no good your reading will be very far from what we should get .

By experience these test do not work on Super Reverb Transformer or other with 2 ohms Output Transformer impedance

You can do this test on unknow OT to see how / where you can use it

[Latole]

Other way I never try:

Part 1 of 2

 How can we test the output tranny?
This is perhaps the simplest and roughest way to test an output transformer, requiring only a multimeter or DVM.
On the plus side this simple test returns a lot of information. On the minus side the low frequency used, mains 50Hz, means that the results have to be interpreted cautiously.

The basic idea is that we drive the output transformer by connecting the 6.3 volt heater winding directly to the speaker winding on the output transformer.

The caviat is that many output transformers don't perform well down at 50Hz. A tranny in a nominal bass amp may give very realistic figures, but a tiny tranny from a small practice combo may not have a lot of response at this low frequency and not give a clear indication of faults such as a shorted turn. While some results may be rubbery this test is still useful to sort out the seriously dead ducks.
Again, the output transformer must be fully isolated. If the output tranny has a selection of output impedances, feed the heater voltage across the largest one, typically 15 ohms, using the whole winding.
When powering up use the 15 watt load limiter first. You can use a larger wattage lamp to bring the voltages up a bit if they are too low to easily measure, the heater line in particular.
The voltages you are particularly interested in are the driving heater line voltage, and the voltages either side of the center-tap - caution: these may be hundreds of volts.
Carefully and accurately measure and record the voltages on the speaker and valve side of the output tranny. If there are no signs of distress you can step up to a higher wattage lamp for higher and more accurate voltage measurements, but do not run this arrangement for extended periods, only a minute or two at a time.
You should now have three voltages; the voltage on the heater line driving into the speaker-side of the output tranny, and the voltage measured either side of the centre-tap on the valve side. These latter two voltages should be close to equal.


Turns ratio
Since output trannies are specified in terms of primary and secondary impedance we need to convert our voltage measurements into an impedance ratio.
The first step is using these voltages to find the voltage ratio (and thus the turns ratio of our output tranny).
The turns, or voltage ratio is equal to the total (anode-to-anode) valve-side voltage, divided by the total speaker side voltage.
Turns Ratio = Vp-p / Vspkr
This will typically be between 20:1 and 35:1.

 

[Latole]

2-2


Impedance Ratio
The impedance ratio is the square of the turns or voltage ratio, so if we take the number found above and multiply it by itself we will have the impedance ratio.
Say we found the voltage ratio was 20:1, then the impedance ratio will be;
20 x 20 = 400:1
What this means is that for every ohm of load we will present 400 ohms of load anode-to-anode. If we connect an 8 ohm speaker cabinet the plate-to-plate impedance will be;
400 x 8 = 3200 ohms.

Power rating
How can you tell the power rating a transformer?
Note: Strictly speaking power in a DC circuit is measured in watts (W), while power in AC circuits is quoted in Volt-Amps (VA). Since transformers are inherently AC devices they are rated in VA. The reasons for this need not concern us here, and you can read guitar amp transformer VA ratings as “watts” without significant error.

This is actually quite a difficult thing to determine simply.
The most obvious method is find the manufacturers data sheet and look it up. If it's an A+R (OT or PT) or Ferguson (OP, OPM, PF, or PVD) type, see if you can find the type number in our listings.
But many trannies have no markings at all.
The power handling of a transformer is mainly determined by the core - the bigger the core, the higher the power.
In the old days (1940's) there was a graph in the ARRL Handbook that allowed you to estimate the VA-rating of a stack (of laminations) from the cross-section area of the centre limb of the core, the part that passes through the middle of the windings (and is thus the most difficult to measure accurately).
By the 1960's newer grain-oriented steels were being used that had higher power handling and only helped to confuse matters. These trannies were smaller for the same power and the graphs no longer held.
So most tech's guess from experience. One way to get some instant experience is to look through component catalogues at the transformers, and check out the size and weight for each of the various power ratings (maximum voltage by maximum current if not given in VA or watts).
If the tranny is in an amp then you get some clues at least from the type and number of output valves (if not from “Gunge-50” written on the front ;).
If you really want to know for sure, then the best way is to measure it.
One way is to load up the tranny until the voltage drops by 5%. The trouble is that different windings, heater and HT, will have different drops giving different values.
The real bottom-line test is to load the tranny with light globes to some value a bit less than you guess its ratings might be, then measure its temperature for an hour or two. It should be no more than 50°C in 25°C ambient.
The most reliable way to test an output tranny is to drive it with a suitable output stage into a dummy load, again watching the temperature carefull

[sluckey]

Uncle Doug can teach you...

     

&t=1691s

[dude]

Shooter, mow the grass...? The grass is dead, two weeks of 100 degrees. Plus l’m lazy. 
Thanks for the lessons all, l love Uncle Doug, makes me laugh every time, love his cats and of course can’t forget his beloved dog.
Just hoping someone already did the math, so l could just sit in the air, sipping on my Dogfish, 60 minute 

[Latole]

Uncle Doug can teach you...

Easier to look at a video than read. Thank you for sharing. I never see this video

     

&t=1691s

[shooter]

The grass is dead, two weeks of 100 degrees

ya, I love the brown grass days, we're only in the low 90's with equal parts water and heat, but driving the mower fast without blades running cools you down 

[Latole]

Close to 90 here in south Quebec province. I love that, cold winter is alway too long

[shooter]

cold winter is alway too long

yup, I just follow the birds till it's warm again 

[Latole]

cold winter is alway too long

yup, I just follow the birds till it's warm again 

I wish I can do.