MC2505 Power Transformer Testing

[MACKIE1975]

What is the expectant ohm reading when probing between red and red wires?
The transformer is by itself without connecting to anything.

 

[CruzBay]

Couldn't guess what it should be, hopefully someone who knows will chime in, soon.

I'd look at the resistance between red and red/yellow, (on both sides) and expect it to be half of what you see from red to red.

And I'd expect either red to red/yellow numbers to be close.

 

[MACKIE1975]

Per my understanding, it should be dead short or very low low resistance.

 

[clinic-audio]

Value depend of tool used to make measurement
what is the problem with this power transformer ?

 

[MACKIE1975]

Suspecting, there is an open on the secondary winding between 2 red wires terminal

 

[MACKIE1975]

Measuring center tap to one red wire does show 8.3 ohm but the other red wire to center tap shows open (OL)
Just using the Fluke meter for continuity test.

 

[UncleBingo]

You CAN check that with an ohm-meter. Measure from the re wire to the center tap on each side. Should be roughly the same. If it's open it will be waaay out of whack with the other half.

 

[mnmmt]

I have my 2505 on my work bench now. With the pt in circuit i am measuring an equal 15.4 ohms between each red wire and the center tap, and 30 ohms between the two red wires. I would probably get different values by taking the wires out of the circuit, but each half of the winding is giving an equal resistance to center tap.

 

[MACKIE1975]

Thanks all for confirming the reading. A used MC2505 power transformer is hard to come by. I am thinking about harvesting all the parts so others can rebuild their own MC2505.

 

[mnmmt]

You may be able to get it rewound or find a new production replacement similar in specs. If you know the output voltages, i would expect most transformer winding shops could rewind it. Heyboer transformer is one, and i have heard there is one in Wisconsin as well see more info here: http://www.roger-russell.com/autran.htm

 

[MACKIE1975]

I have been searching around for a rewinding service without any luck or service cost is really high.
Thanks for the link. I will try one more time with this link and will decide parting out or rebuild.

 

[MACKIE1975]

I got a reply on one of the transformer rewinding service.

"McIntosh had both power and output transformers .... on C core. . It's a lot of labor doing this. Another option is to remove the original and wind a new EI style core and pot that in the original can"

Is there pro and con between C core and E&I core?

 

[clinic-audio]

Hello

I will choose rewind service on C core
power transformers does exist in EI when the MC2505 start .
Why MCINTOSH don't use EI transformers in your point of you ?

 

[MACKIE1975]

EI transformer may change the sound signature of the MC2505.

 

[mnmmt]

I think the C core may be slightly more efficient electrically, but I can't imagine the power transformer really changing the sound much if it puts out the proper voltages.

 

[calman46]

I would connect just the transformer to a DBT to be sure. The diodes are disconnected correct?

 

[MACKIE1975]

When I started the thread I did mention the power transformer is not connecting to anything (circuit). It is on the table by itself

 

[calman46]

Does it flunk the DBT ?

 

[MACKIE1975]

Only did WRT, OCT, SCT

 

[nj pheonix]

Does it flunk the DBT ?

If it reads open as the OP stated, something in the Tranny failed.