OT secondaries odd colors (unknown leads)

[dude]

I have a 50 watt OT from Magic Parts, 2,4 and 8 ohms they listed but they can provide no data on the color code of the secondaries. I tried to use a 9V battery to get the winding ratio and then find the impedance, doesn't read any voltage between the plates and the secondaries. Does the voltage provided to either the secondaries or plates have to be the same on each side? Can't use a battery's + and -.  Does a  variac or a low voltage power transformer have to be used?
Could I use a HV power transformer in a working amp, disconnect the 6.3 filaments supply and attached those wires to the unknown OT's  plates (check the exact voltage across each lead) and read the lower secondaries voltage (probably will be mA's) to get the impedance ratio?   


This Magic Parts TF125 OT has four secondary wires, Black (assumed ground ?) white, green and green w/yellow stripe, (listed as a 2,4,8 ohms sec.) I'n not even sure the black is ground, could it be the green w/yellow stripe...? Don't want to damage  the OT, I bought it new many years ago, never used.  Any help appreciated. 

[PRR]

Transformer will not pass steady DC voltage. All you will get is a dead battery.

Yes, put AC to the plate side, read *all* the voltages on the secondary. 6VAC from a heater winding is generally safe.

> read the lower secondaries voltage (probably will be mA's)

mV. Keep your units straight or you will get lost.

[Latole]

This is how I test OT. It is a complete test ; transformer input and output impedance.

 You can use a 6.3 AC volts as PRR write

Testing Output Transformer

1- Signal generator set to 1000 hertz AC 0.5 volts .
    a- You can use a 6.3 AC volts as PRR write ; check with meter . For calculation, replace all my 0.5 AC value for yours

2- Send this signal to OT secondary( note 1 )  check with accurate meter to have 0.5 VAC *on OT tap. Or close
    *do same if you use  6.3 AC volts
     Note 1 ; multi output; chose a pair of wire you dont know, use same common

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 Specs 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

[dude]

Transformer will not pass steady DC voltage. All you will get is a dead battery.

Yes, put AC to the plate side, read *all* the voltages on the secondary. 6VAC from a heater winding is generally safe.

> read the lower secondaries voltage (probably will be mA's)

mV. Keep your units straight or you will get lost.

Thanks PPR, one other question. On the OT l'm trying to find the secondaries ratings, can l assume the black wire is ground, another words keep one lead of meter on the black as l check  voltage on each wire, white, green and green/yellow?


Also, l would attached each of the 6.3 a/c supply filament wires to each plate wire of OT and expect to see around 6.3 volts, (meter across these connections) but whatever it is use that voltage in finding each secondary winding ratio.


I should know this but better to be safe then sorry.

[Latole]

6,3 AC must got at seconday , not primary ( Plate )

More here:
https://www.ozvalveamps.org/repairs/trannytest.html


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.

[sluckey]

6,3 AC must got at seconday , not primary ( Plate )

Not so. It can go on either side. But in this case it MUST go on the primary. Why? Because he is trying to determine which secondary lead is which. He knows the three secondary taps are 2,4,8 but doesn't know which is which. Putting the voltage on the primary will give different voltages on the secondaries that can be used to determine which lead is which.

[Latole]

6,3 AC must got at seconday , not primary ( Plate )

Not so. It can go on either side. But in this case it MUST go on the primary. Why? Because he is trying to determine which secondary lead is which. He knows the three secondary taps are 2,4,8 but doesn't know which is which. Putting the voltage on the primary will give different voltages on the secondaries that can be used to determine which lead is which.

You must be right.

[dude]

He is right, I used the 6.3v to primary plates as to not deal with higher voltages on the secondaries, much eaiser to do o nthe primary,so:

I got a ratio of 23:1, green sec, 32.5:1 green/yellow sec and 44:1 on the white sec.


I know this OT is for a Super reverb, Bassman and the like (pair of 6L6GC's in AB1), I know the sec output is 2,4, and 8 ohms, just like what Sluckey said, don't know which color wire is which.
Now, I know that my plate voltage on a pair of 6L6GC in class AB on the amp I will use this OT is going to be about 420/425v.  Looking in a tube manual, I see all kinds of impedance's for the 6L6GC's, depending what class they run and VOLTAGE, different impedance's for different 6L6 types too, I always though that as basic rule 6L6GC want an OT impedance of about 4000k with a plate voltage of 425v (am I correct here?)
So it looks like two 6L6GC's running in class AB @425 v on the plates would run well matched wit ha 4000K impedance OT. If I am correct, then the Green tap would be for an 8 ohm load, the Green/yellow tap for a 4 ohm load and the White tap for a 2 ohm load.
At least I believe this is how Sluckey explained this to me a few years ago.


I see class AB1, AB2 in the manual, what is the difference?
Correct me if I'm wrong.

[sluckey]

Man you really mangled that!

KISS... The highest voltage is the highest impedance. etc, etc.

[shooter]

AB1, AB2

illiterate version,  the higher the #, the closer to class B you get.

[dude]

Man you really mangled that!

I'm out to lunch here? Sh*t, you sound like you're telling me to take a hike, a beer or two not....

[tubeswell]

I got a ratio of 23:1, green sec, 32.5:1 green/yellow sec and 44:1 on the white sec.

 Correct, if you want a 4K load, then 2R speaker on the white wire, 4R speaker on the green/yellow wire, or 8R on the green wire.

[2deaf]

I see class AB1, AB2 in the manual, what is the difference?

You use AB1.

Had you connected the 6.3V to the secondaries, the highest voltage on the primary would be when you connect the voltage to the 2 Ohm tap.

[dude]

Thanks tubewell, l just assumed from the data page that with 425 voltage on the plates, 4000k was the best OT impedance for that tube at that voltage.
And Sluckey, l'm only on my third Golden Monkey, but l might technically say the wrong thing, sorry. I'm just a old dude that still loves music, l might not be the best player but l had a fair share of highlights in my life on stage.  I appreciate "all the help you have given me". I may be redundant but l'm am old fart who loves music and has gotten in over his head on building amps and the like, l know squat. But we're all human beings, knowable or not, piece brother. 

[DummyLoad]

is this your part?

doug used t sell these as well.


New Sensor Corp.


NSC018343
40-16930


primary impedance 4.2k


Lamination: 3 3/4", Stack: 1 1/4"


Mounting on: 3 1/4" x 2"


Overall dimensions: W x H x D: 96mm x 79mm x 80mm


Primary:
   A1 Blue
   HT Red
   A2 Brown


Secondary:
   0 Ohm Black
   2 Ohm White
   4 Ohm Yellow/Green
   8 Ohm Green

--pete

[sluckey]

Please excuse me. I'm the one that is mangled. 

[PRR]

> Signal generator set to 1000 hertz AC 0.5 volts .
> Send this signal to OT secondary
> Read AC voltage at OT primary

An objection is that many sig-gens are 50 or 600 Ohm output, and will not drive 4-8-16 Ohm secondaries for-sure. (With "2 Ohms" as an extreme case which may "not work", depending on specifics.)

OTOH the tube-side is 2k to 8k and an easy load for most signal sources.

400Hz or 1kHz are nice audio frequencies, but be SURE your meter responds correctly. For a while most "RMS" meters did NOT work well on higher frequency and lower volts. Whereas we can be confident on 50/60Hz readings.

Driving primary and reading secondary we expect ~~30:1 step-down. So we need to start with a high voltage to be sure we can read the result. In old days we needed nearly a Volt! (Unless we had the very expensive Ballantine or H-P ACVMs.) Modern (even cheap) DMMs at 50/60Hz will read pretty small. 6V through 30:1 makes 0.2V. Enough for jazz.

No, you can't assume "4K for 6L6" because happy loads depend on voltage and power and distortion. Yes many guitar amplifiers like 4K, but a lot don't. It helps if you feel sure it is a 4-8-16 sequence, but as Latole said there are 2r and other odd tappings.

Read all the pairs of leads looking for the highest. If you expect a 4-8-16 sequence that may be 16r. Then go back and look for a pair which is "half" of that max voltage (4), and a pair which is 0.7 of the max (8).

As the Dummy says, it may not be 4-8-16.

[2deaf]

...piece brother.

Remember when Country Joe said, "I don't know how you're ever gonna stop war if you can't spell peace any better than that"?  Or wait a minute......Remember when Jimi would flip a peace sign and then turn it upside down and flick his tongue at it?

[dude]

Well, after three Golden Monkeys, four now and  some Jack, maybe something else,  .  My spelling might be a little off, like l said before, one can walk into the other room and forget what he went for...
We're you there at Country Joe and the Fish, I was? Cheers brother "Peace"

[shooter]

Country Joe and the Fish

Loved learn'n spelling for him