Mayday to all Power Transformer Guru...

[Tubetwang]

Have these two PT but can't figure out which lead/tap is what. The black one was, according to the seller a PT in a Hammond 2x6V6 and the other was a pull from a Grundig console with 2xEL84.

Any tips on a web sites or infos on how to find the two power, the 6.3V, the 5V taps, if any, would be great and extremely helpfull.

I've Google and searched but cannot find any info.
It may be too newbish a question?:oops:

Thanks for any leads...

[rfgordon]

Not an unreasonable question at all. While there is somewhat common color code, not all makers stick to it. Plus, PTs wound for multiple voltages (120, 220, etc) can be vexing.

Generally speaking, black wires (or variations, like black/white) are primary leads. Yellow is ususally 5 v rectifier heater tap with no center tap.

Green (and variations) should be 6.3 v heater taps, with or without a CT.

Reds (and variations) should be hi volt taps, with CT and perhaps a bias tap.

You can always do it the hard way: If you know the primary wires, connect them to power cord. Attach each of the other leads to a point on a block of connectors, power up and start measuring voltages. A HAM buddy of mine has a set up just for this purpose.

Good luck.

[CaseyJones]

Have these two PT but can't figure out which lead/tap is what. The black one was, according to the seller a PT in a Hammond 2x6V6 and the other was a pull from a Grundig console with 2xEL84.

Any tips on a web sites or infos on how to find the two power, the 6.3V, the 5V taps, if any, would be great and extremely helpfull.

I've Google and searched but cannot find any info.
It may be too newbish a question?:oops:

Thanks for any leads...

A Grundig typically won't have a 5 volt winding so you won't have to worry about that one. Same for a center tap on the filament winding.

My guess is that you have 7 leads on your transformer. Two will be 6.3 with no center tap, two will be HV with a center tap, two will be your AC primary. There's a wild card on Grunding transformers, yours might be a Euro spec unit with a 240 volt primary OR the primary may be tapped.

Start by doing continuity checks to see which windings connect and which ones don't, that should result in three sets of wires.

Color codes if any might be a clue which is which.

Any seller worth buying from should have taken notes when the transformers were removed. Parts without documentation are generally considered junk.

[Tubetwang]

Thanks for the swift reply guys.

I forgot to post the picture i took of the two transformers.

The Black one has 10 taps, one resistor across 4 and 7, blue wires on 2 and 6, two yellow wires on 5. Small part of cut white wire on 1, and small part of black wire on 3. I plugged 125 volts on them 1 and 3 and burnt my Triplett Auto meter, ordered another one from Parts Express, will be more carefull nest time...

The Grundig has 6 wires on top and 6 wires on bottom.

[LeftyStrat]

DO NOT USE WALL VOLTAGE!!!!!!

Here's why. The normal ratio between primary and heater windings is 19:1. If you apply 120 VAC to the heater windings, this is a multiplier rather than divide:

120 / 19 = 6.3 VAC

becomes

120 * 19 = 2280 VAC

For the hammond, I'd remove the resistor and wires, and then make a little chart. Clip a lead to terminal one, and measure and record the resistance between that point and all others. Do the same for the rest of the points.

Without connecting the transformer, you can measure resistance and determine a lot. For example, you may measure between two points and get something close to 160 ohms, and then find another point that measures 80 ohms between each of the other two, you've found a center tap and the two outer connections of a set.

Any two points that do not share a resistance with any other points have no center tap and are a candidate for primary connections.

So something a bit safer than connecting wall voltage is to use a filament transformer or the filament voltage from another PT with the other leads taped off. Then your not dealing with voltages that fry your meter (or worse).

Then from the above example, 6.3 VAC applied to the primary:

6.3 / 19 = .33 VAC

or applied to the heater end:

6.3 * 19 = 120 VAC

Just remember, a transformer is nothing more than a bunch of ratios, and these work both ways, one way they divide and the other way they multiply.

You really don't want to be working with 2000 volts.

[Tubetwang]

Hey Lefty thanks a lot!

You guys are great!

I took the bell off and was putting some 124 ac to what seems to be the two ac main (black and white cut wires on the bell) that were the black and the brown under the bell) and was measuring away with my new meter, when i looked up the computer and saw your post.

I will do according to you post.

For the record, i post a picture of the tranny with bell off.

Thanks again!

[LeftyStrat]

The calculations can be even easier if you have a signal generator. One volt AC in, voltage out is your multiplier/divider ratio.

And yes, I have fried a meter also before I learned the safe way to do it

Hopefully your meter was fused and you should be able to replace the fuse have it work again.

If you post your resistance measurements, we can help you figure out what is what, and maybe I can use them as an example in an article I want to write about measuring transformers. Actually I've already started it, maybe it can be an AG wiki entry.

[Tubetwang]

Thanks for the help Lefty.

I've been at it all week trying to figure it out...i tried with adding another tranny (hammond 167M5) for the rectifier, as the Hammond was apparently in a 2x6V6 with diodes...many combinations...nothing worked...blew a fuse...(blew my Triplett meter, opened it and the pcb was black, kept the two fuses but).

I took some readings and found the two ac in and went at it all day but nothing worked. Hey but i got the 5E3 rectifier to light up.

Sooo, i guess i better offer my trannies to anyone who wants them...

The Grundig P.T. was in a Console with short wave, am/fm, record player etc. Its a Grundig SO132 WE (EM34, ECC85, ECH81, EBF89, 2xECC83, 2xEL84). I ordered the Tannenbaum schematic that i'll include. Probably early 60's.

The Hammond like tranny was powering a 2x6V6 with diodes.

I also also have a rare European 220 only Dynaco SCA-35 P.T. 10128 from 1966 that i don't need. That was powering 4xEL84. I have the amp schematic.

If anybody wants these they can have them. They only pay shipping.


If not, i'll give them to the scrap metal dude...

[Tubetwang]

Here's the resistance measurements for your articles Lefty...

Red to brown 83.2 ohm
Red to green 0 ohm
Red to blue 174.8 ohm

The trannies are gone to the scrap metal man.