DC Resistance differences on Mod. XFMR

[Jeff W9GY]

I have a UTC S-22 modulation transformer and was checking the DC resistance on the primary between center tap and both modulator plate connections.  With CT being pins 9&10 and plate connections being 8 & 11 respectively, I measure CT to 11 = 76 ohms and CT to 8 = 68 ohms.  The difference bothered me, but then I realized that the two windings would have different diameters (being wound on same core) and thus somewhat different DC resistance.  Is my thinking flawed, or does that make sense to you modulation iron gurus? Your thoughts, please.     

73s Jeff

[WA1GFZ]

I would put the positive modulation on the low resistance winding because it is closer to the core so tighter coupling to the core and has the highest inductance because there is less air in the core since it isn't spaced away from the core. The winding away from the core will be less efficient so you will get less negative monkey swing.
that is why running a transformer backwards is less efficient.

[W9GT]

Hi Jeff,

You are correct in your conclusion.  It is normal to see some difference in resistance between the two halves of the winding for the reason that you stated.  A more conclusive way to check out the balance of the winding(s) is to apply a low AC voltage to the primary (secondary) and measure the voltage developed across the windings you are checking.  It is also sometimes useful to utilize a megger to check out the windings by measuring breakdown resistance between the windings and between the windings and ground.  It is also very useful to record the DC resistance of the windings for future reference if you have problems or suspected problems with the transformer later on.  You can then compare the readings and perhaps locate a fault if you notice a difference between present and former readings.  I located a defective winding in my 30K-4 mod iron that way.

73,  Jack, W9GT