Trying to ID/pinout a tranny - Need some help, please...

[Brossman]

Hey guys,

My buddy gave me a tranny from a reel-to-reel that he said ran a twin-diode (rect) and two 12ax7's...

Anyhow, can't figure out the pins/contacts, nor have I had any luck locating a datasheet.  Can I use my analog multimeter somehow?  Either way, here are some identifiable traits...

- one side has 2 leads - green and green/white
- other side has 5 leads - 3 red/white, black, and red/white/blue
- Cloth-wrapped leads
- Weight ~3-4 lbs. (just a guess...)
- Approx. Dim: 6.15cm (2.5") x 5.5cm (2, 3/16") x 6.2cm (2.5")
- three number-sets on the side, as follows:

68P138-1
27P79
892325

Thoughts?

[Skruffyhound]

You're never going to find it from those numbers. Those are just in house manufacturers codes from the 70's probably.
If you want to use it you'll have to measure it yourself. Which involves some safety issues and some slightly specialized equipment if you really want to know what it can do. Check out this : http://www.radioremembered.org/xfmr.htm for a readable intro, albeit radio related, and this : http://home.earthlink.net/~jimlux/hv/xfmrmeas.htm for more detail and a good idea about testing with a scaled low voltage. The idea is to use for example 11.5 V if you have 115 VAC in your wall. Only apply low voltage to the primary, if you apply it to one of the secondaries you can still get a huge voltage out of the primary.
I'm an absolute beginner with transformers, PRR will be by in a minute and set you straight.
My advice - if you aren't very clear about safety and theory on this, stick it in a box and come back to it a bit later. Or perhaps just bin it and salvage something newer. If you are wanting to build an amp I'd just buy the transformer the project calls for, why take chances.

[Brossman]

Well, the simple answer is that I don't have the money.  I'm also interested in designing new amp circuits with (almost entirely) salvaged parts.

I have recently aquired a laboratory power supply... could I use this to test what's coming out the other side? or could this be dangerous?  I believe the P/S IS current limited, but I suppose I cannot be too sure.

[Skruffyhound]

I have no idea what experience you have, so you need to decide for yourself if you can do this. Wall current AC can knock you down dead. I suggest you read the safety procedures at some of the amp forums and procede with extreme caution. The links I posted will give you some ideas how to test. Good Luck

[thedefog]

You could build a lightbulb limiter to test it out. That's how you test out transformers with low voltages when building tube amps.

[Mark Hammer]

Since you don't know what it is, then you don't know if it is relevant to things people around here do.  In which case, save yourself the aggravation of trying to track down info on it.  The chances are VERY good that it will be useless, either by virtue of its pecs, or by virtue of what might have been done to it during removal.

Once upon a time, there was a kind of universal semi-conductor cross-reference in print, that used 6pt font and onion-skin paper, but still managed to come in at around 10lbs and several thousand pages.  It included house-numbers as well.  But since the last time I saw one of those in the mid-80s, you can imagine that a) the number of semi-conductors and house-numbers in existence has likely tripled, b) organization of the contents can easily take 5 years to accomplish, and c) there is no earthly purpose in producing such a cross-reference in paper form.

Of course, since it is an older component, if you were friendly with someone at a university tech lab, they might have such a thing hanging around from the 80s, gathering dust in the back.

For future reference, it is good to have a DMM around with a socket for testing transistors.  One can easily identify whether something is NPN/PNP, and their pinout, using the transistor testing function.

[Skruffyhound]

You skimmed the opening post didn't you Mark , caught me out too until I noticed the number of leads coming out of it.

[Skruffyhound]

thedefog - yeah, I think that's included in one of the links I gave.

[PRR]

Assume that is _IS_ meant to take wall-voltage and power two 12AX7. That means it won't build you a 100 Watt amp, but maybe a preamp or booster.

Use Ohms function to learn what is connected to what and how many Ohms.

Draw a picture!! With wire-colors and ohms between them.

You may have three leads on one winding. The ohms will be like 130 - 260 - 135. Obviously the 260 ohms is end-to-end, the 130 are each side of a center-tap.

The final Voltages will be _roughly_ in order of the Ohms. The 6V winding will be near 1 Ohm, the High Voltage winding will be hundreds of Ohms.

The secondaries are presumably about 6V or 12V and 250V (or 500V CT). The primary is wall-voltage. What land did it come from, 120V or 230V land??

If 120V, there is no real confusion between 120V wall-voltage winding and 250V high voltage. If wound for 230V, it gets trickier. However _if_ friend is correct that it was a 2 diode affair, the HV is probably 3 leads 500V CT and much higher end-to-end Ohms than the wall-voltage winding.

When you have a good guess what each winding is, get a small 6V to 12V AC power supply. This may be a filament transformer from Radio Shed, a tap from a tube amp, or maybe an AC wall-wart. No, a DC supply will NOT work.

Apply the 6V AC to the presumed 120V wall-winding. Listen for loud hum from AC supply and shut-down quick before it burns. If happy, measure voltages at all windings. Do NOT get your fingers on the leads or probe!! If you guessed wrong you could have hundreds of volts. If you guessed right, for 6V AC into a "120V" winding, you expect 0.3V across "6V" heater winding and 12V across "250V" windings. For nominal 230V, abut half these numbers. Check your actual "6V AC" voltage too.

These voltage-ratios will stay the same when you apply higher voltage on the wall winding. So from these numbers you can compute actual normal outputs. These will be un-loaded values. Expect a "6.3V" winding to be 7V unloaded.

If the HV winding is 500V CT (250-0-250V), and you use the conventional 2-diode rectifier and a filter cap, the DC voltage will be 350V. Economical filtering is several R-C stages, typically dropping to 300VDC or 250VDC by the time the DC is clean enough for low-level audio.

[thedefog]

You could also try the grope method. That's what Paul Hogan did in Crocodile Dundee.

[Mark Hammer]

You skimmed the opening post didn't you Mark , caught me out too until I noticed the number of leads coming out of it.

Ohhhhhh....THOSE "trannies".  Never mind.

[Brossman]

@ PRR

Thanks so much! ...and yes, I understand it will only charge a preamp (or something similar).  However, that was my intention.  Someday, I'd like to build it and the amp I design to function with it into a small (maybe practice?) amp, adding on a separately supplied power amp.  I assume that if I indeed DO have a separate supply on the power amp, that would allow me to push into some greater ranges (perhaps, 20-30W)?

Ahh, but I drift from the subject at hand...

@ Mark

Yes, I should have clarified.  There are three kinds of trannies - two of which are commonly spoken of here on this beloved forum.  I guess I need to implement different vocabulary, however, I was unsure if the phrase "lead-out" would've sufficed. 

@ Skruffy

Thankyou so much, the information provided in those links will be invaluable.  Yet, as school takes up most of my "available" time, I will be somewhat unable to take a look at this as well as many other of the pursuits I'm currently involved with.  As soon as I make some headway on this, I will likely post another thread to discuss the possibilities of using it.  Should that topic (an amp) be applied at another forum?

[Skruffyhound]

A post in the "lounge" would be fine, the main board should be mostly pedal related. Good luck