Trouble with power transformer: uneven voltages

[Enzo]

Welcome, Marvino. But I don't think so, read the whole thread.

Windings with two red wires at the ends or two red/white wires at the ends are meant to be symmetric.

I think whoever wound the thig looked at the original spec with a tap 45v away from the CT, and misinterpreted it to mean a 45v winding BETWEEN the CT and the rest of the winding. In other words, the winder didn't understand the tap was to take off only one side.

[Bruce / Mission Amps]

{[I] I ordered a Tweed Bassman Chassis from Mojo and was (A) charged twice when they didn't include it in my first order (this was never resolved - they took the stance that they couldn't possibly have made an error like that) and (B) The Chassis was so poorly made that I hate to use it for anything. It looks like a problem waiting to happen. RE

Personally I've had very very few goofs with orders from MOJO and never had an issue not get resolved with one or two calls but if any vendor called me a liar and stone walled me I would contest that "charge" to the ends of the Earth and make sure they knew I would negatively comment about them and the snafu every time I saw their name being mentioned in an open forum.

Also, I wonder how long ago this poor chassis was made? Although I do not use MOJO for my custom made chassis, MOJO has been using a different chassis shop for a while now and they look pretty good... is yours polished stainless steel or a chassis with a spot welded on face plate? If so, I think that was an old manufacturer they were using a couple-few years ago.

[slidincharlie (Carlo P)]

New measurements on the secondary leads

I’d like to summarize the situation and offer a little more food for thought.

Thanks for doing this, Tom.

There is no doubt that this second transformer is faulty. It was manufactured incorrectly. When it is hooked up per the supplied spec sheet, the two halves of the high voltage AC secondary are 46 V out of balance.
In entry #4 Carlo posted the open circuit secondary voltage readings. The readings show:
1) One side of the HV secondary is 46V higher than the other. Therefore, the “center tap” is NOT in the center.
2) The bias tap is at 46V with respect to the wire color coded as the center tap

I have redone the measurements and confirm the above readings and the 46V unbalance (readings now are a little higher than in my first measurements (post #4), due to higher mains voltage).

Given the fact that the imbalance voltage is exactly the same as the bias tap voltage, we speculated that the bias tap and the center tape wires may have been misconnected inside the core. Carlo took the voltage readings again (See thread entry #6) and reported the following:
“Pretended that the RED/BLU bias tap was the center tap.
Result (with the wires in air): I have exactly the same readings but inverted: the wire that gave me the higher VAC reading now gives me the lower, and viceversa.”.
This still doesn’t seem possible to me and the reason I am continuing my discussion is because of the possibility that it’s still a mislabeling of the RED/YEL center tap lead wire and the BLU/RED bias tap wire.

I confirm the above: using the RED/BLU bias tap as it were the CT, gives me inverted readings.

(...)So Carlo – I still wonder if you got the two red wires mixed up when you took the second set of readings. Easy to do since they are both red.

Nope. In this new set of measurements I have marked the RED wires and confirm the above results.

If you are willing, I’d like to know what the voltages on each secondary lead is if you measure them all with respect to one red lead. (Put your common test lead on one red wire and leave it there as you read the voltage on each of the other leads of the HV secondary winding) Do you have the time to indulge me?[/FONT]

Tom, I did it. These are the results (I haver labelled each lead so I couldn't mix them up, and used either RED lead as my reference lead):
RED2 to RED1: 714 VAC
RED/WHT1 to RED1: 640 VAC
RED/WHT2 to RED1: 74 VAC
RED/WHT1 to RED2: 74 VAC
RED/WHT2 to RED2: 640 VAC.

Does this help?

[Alex R]

Pardon me for butting in but I think the voltages we're really interested in are RED1 to RED/BLU (ie 'bias tap'), and RED1 to RED/YEL (ie 'centre tap').

[Enzo]

Alex, check posts 4 and 6. Red yellow and red blue are 46v apart. WHichever one you chose as center tap leaves one red end 46v higher than the other end. Only difference is which one you chose determines which end is high.

The point where the true center tap should be is the center of the 46v segment. The tranny maker essentially split the whole winding in two at the center tap point, inserted 46v worth additional winding. Now the R/Y and R/Bu are at either end of that instead of R/Y in the center.

The spec was I am sure for a tap 46v from center on one side of the winding. What the winder made was 46v in the center of the winding.

Or look at it this way: I have a 300v battery, a 46v battery, and another 300v battery wired in series. That is 646v of battery. The junction of the first two batteries has a R/Y wire trailing out. The other junction has a R/Bu wire trailing out. If you measure voltage from either end to one of the wires, one end of the stack will be 46v higher than the other end. Then use the other wire and the same difference will occur except at opposite ends. These are magic AC batteries so polarity doesn't enter into it.