Polarity on a non-bladed plug?

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1) Reversed AC polarity -- All power transformers have an inherent asymmetry to their construction. The primary winding comprises multiple layers, so that one lead is connected to the innermost windings and the other lead is connected to the outermost windings. This means that one lead has a higher coupling capacitance to the core of the transformer. Please remember that the AC supply is also asymmetrical, with the neutral lead essentially being at ground potential (assuming there is not a fault in the house wiring). The result is that one orientation will give a higher AC leakage current to the chassis of the amp (and worse sound) than the other orientation.

Not all transformer manufacturers use consistent markings on their transformers so that the correct orientation can be identified, and not all amp manufacturers pay attention to this even if the transformer is correctly marked. The result is that many audio products have a random chance of being correctly oriented.
Charles Hansen
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What you say may be true Jea but if the plug is not polarized then it should'nt matter. If it does, turn it the other way.

Wow I didn't think my thread would produce so many responses. All great info and I'm thankful.

Jea48, if you actually measured the 'potential' at neutral or ground, you would find that it it varies from positive to negative at 60 Hz frequency, thus making it symmetrical! Capacitance (and inductance, for that matter)only exists in AC circuits where polarity essentially changes 60 times a second. Can't be more symmetrical than that. Hum, however, can exist due to different potential at the ground or neutral at different places. That is why reversing 'polarity' might make a difference.

Bob P.

I use a high-quality digital multimeter to check. You need to measure for residual ground voltage at the RCA jacks. Make sure nothing is hooked up to the component but the power cord. Try plugging it in both ways while noting the voltage reading between the RCA hole and outer ring on one channel (hole is positive). The lower voltage orientation has the polarity correct.

I did this with my vintage MC240 tube amp that had 1960s lamp cord for its power cord. One way I got like 35mV and the other way I had 6mV. I have to say I couldn't tell a difference in sound though but I am anal so I wanted it correct for peace of mind.

By the way, whenever making a low-level voltage measurement, you HAVE to use the local ground that is as close to the positive as possible. Using the outlet ground (or chassis) will do nothing but screw up the results.

Arthur