fuse burning with two alternate power transformers

[sbirkenstock]

Hi Everybody,
I got an EL84 amp working.
It currently uses a ClassicTone 18056 power transformer.

Since this is not available no longer, I bought two replacement power transformers for sound testing.
One is the TAD MJTM18WP and the other one is a TubeTown tt-ma18pw.
Surprise: with both of these PTs the main fuse is burning.

Questions:
here from the TAD website:
Primary:
120V Grey
110V Brown
0V Blue

120V White
0V Black

Secondary:
290V@120mA Red
0V Green/Yellow
290V Red

3,15V@3A Green
0V Green/Yellow
3,15V Green

6,3V@2A White
5V@2A Orange
0V Yellow

I wire for 240V. Does it matter if connect Grey (120V) with White or Black? Isn´t that interchangeable? (it´s just a coil, right??)
I got Black and Blue going to 240V AC and connected Grey and White.

Actually all three PT measure slightly over 12 ohm for the primary.

Is it ok if I only connect the primary side for testing?
Of course making sure that the secondarys are all isolated and not touching anything.
That would be like pulling all tubes incl the rectifier?

I did give it a try, fuse still buring up. (Only tried this with the TAD)

Any other hints?

thanks a lot,
Stephan

[pdf64]

Primary:
120V Grey
110V Brown
0V Blue

120V White
0V Black

Secondary:
290V@120mA Red
0V Green/Yellow
290V Red

3,15V@3A Green
0V Green/Yellow
3,15V Green

6,3V@2A White
5V@2A Orange
0V Yellow

I wire for 240V. Does it matter if connect Grey (120V) with White or Black? Isn´t that interchangeable? (it´s just a coil, right??)
I got Black and Blue going to 240V AC and connected Grey and White. ...

The phasing of the primary windings is crucial! Get it wrong and the magnetic fields are fighting each other.
Need the transformer info sheet to be sure, but I suggest to connect black to neutral, grey to live, link blue and white, insulate brown.
And for goodness sake, use a light bulb limiter in these scenarios!!!

Edit - the info for both transformers is crap, doesn't note phasing
https://media.tubetown.net/info/datenbl ... pw-int.pdf
https://www.tubeampdoctor.com/en/mains- ... ion=rating

Whatever, the implication is for parallel the 0V ends are linked, for series the 0V of one winding links to the 120V of the other.

[R.G.]

PDF is right - you're having wiring/phasing errors.

Since the documentation isn't good, you might want to treat these transformers as "unknown" devices. At least you know which windings are the primaries. You might want to try this process. It works for any unknown transformer and quickly tells you what you have. In doing any of this, remember that you are messing with voltages that could electrocute you. Work slowly, methodically, and carefully. It's not worth dying for. Don't try this if you're not sure of what you're doing.
1. Identify the windings. Print out the transformers' datasheets. Now make sure the windings are all disconnected from any circuits at all. Use your ohmmeter setting to verify which windings are connected and which are isolated. For instance, each "primary" should have some resistance from end to end, but many, many megohms to any other windings. MARK THIS ON THE PRINTED DATASHEET so you know, and don't rely on short term memory to know that white-gray (or whatever) is one winding. You are essentially verifying the datasheet color codes by doing this.
2. Use a third transformer to put a low AC voltage on one primary winding. It is convenient to use a "12VAC" source for this, but 6.3V heater windings will do, as will any AC voltage less than the 120 Vac specification for one of the "primaries". Measure the AC voltage that you're feeding to the selected "primary" and then measure all of the AC voltages produced by every other winding. WRITE THE MEASUREMENTS DOWN .
3. Do the math. Calculate what the voltage on each winding would be if the "primary" you are using were actually being fed 120Vac from a wall AC mains voltage. WRITE DOWN THE VOLTAGES THEY OUGHT TO HAVE. Now check - do the voltages you calculated match what the datasheet says? They ought to be close.
4. If all is going well, you should be able to identify that the two windings you think are primaries have very nearly exactly the same AC voltage across them. So if, for example, you were feeding 12.6Vac into one "primary", the other "primary" should have close to 12.6Vc across it.
5. Now check phasing. Connect ONE wire from the second "primary" to one end of the powered primary. Measure the AC voltage across the powered primary - for example, this might be 12.6Vac (or 6.3Vac, or whatever you are using). Now measure the AC voltage across both windings, the powered primary plus the two series connected primaries.

If the voltage across both series connected primaries is nearly twice the voltage you're applying to the powered primary, the windings are correctly connected so you could put 240Vac across them. If the voltage cross the two series connected windings is nearly zero, they are connected out of phase. Reverse the wires of the non-powered "primary" and verify that now the voltage is about 2x the powered primary winding.

I've typed this process into several forums a number of times. I guess I ought to do the drawings and text into a document I could just point to.

[Roe]

just change the phase of one of the primary windings

[sbirkenstock]

Thank you for your help!
Yes, changing the phase of one primary helped in both cases.
The TubeTown PT actually had a piece of paper in the box explaining the correct wiring,
I could not find any info whatssoever for the TubeAmpDoctor PT.
Measuring with a 12 AC source worked very well.
With the wrong wiring I measured less then a volt on the secondary, with the correct wiring it went up to slightly over 30 volts.
And I did dig my light bulb limiter out, was not required though