Question on PL700b Transformer Hot/Neutral.

[Vintage 700b]

Hello Guys,
I disassembled my 700b down to the bare chassis, still need to replace the bridge rectifier, and fuse holders. When I disassembled, I noted wire routing and colors etc. At the terminal block, coming out of the transformer, I noted 120v on the left side, and 6 volts on the smaller right side.
I have always worked with Black wire =Hot, White wire = Neutral. I saw a black and a white wire going into this terminal block and cut the wires about 3” long, thinking it would be a simple hook up from line in to transformer later. I am aware of the thermal link, and power switch routing etc. from the fan plug, line in. Also have the correct routing for AC/DC from the bridge rectifier to the rest of the components.
I am posting some pictures of what I have however. I have a Black Wire AND a White wire going to the farthest left post, with an old piece of masking tape around them. Then the other leg into the transformer is also Black. As you can see the actual transformer wires have no colors. My question is which of these leads is Hot, and which is Neutral?
Thank You.

 

[Billboard]

Transformer leads do not have a hot and neutral, your choice on which one goes where.

 

[Gepetto]

You need a polarized line cord to make a difference with this. Wide blade is neutral, narrow blade is hot. With the polarized line cord in place, try connecting each way and then measure the chassis to safety ground at your outlet with your DVM set to AC volts. Measure Hot-Neutral orientation #1 and write the AC volt measurement down. Then flip the Hot-Neutral orientation the other way and measure and record.

Using the measurements you recorded, connect in the configuration that gave you the lowest reading. This will produce the best and lowest overall noise result in your amplifier. Windings on a transformer are physical things and they have to make compromises when winding. You want to take advantage of this when connecting your primary. If you don't have a polarized plug then you will have a 50/50 chance of plugging it in the wrong way and increasing your noise floor.

Make sense? If not ask more questions.

 

[mlucitt]

I wish Phase Linear would have originally done that test and installed a polarized plug. It would have saved us a lot of time.

 

[Vintage 700b]

Hello Joe,
Yes, that makes perfect sense. I was aware of the polarized cord and the blade orientation. I was not sure what to check, as this of course has a 1975 cord on it. I really appreciate you clearing away the fog. I actually told a friend today, "Well I have a 50% chance of getting it right". I will perform the measurements and install accordingly.
Thank You!

 

[Gepetto]

I wish Phase Linear would have originally done that test and installed a polarized plug. It would have saved us a lot of time.

That was before polarized plugs existed...

 

[MarkWComer]

That was before polarized plugs existed...

But take a look at the line cord- what should be the neutral side is ribbed even though the plug isn’t polarized. Whether PL (or any other manufacturer) followed this convention is dubious.

 

[Gepetto]

But take a look at the line cord- what should be the neutral side is ribbed even though the plug isn’t polarized. Whether PL (or any other manufacturer) followed this convention is dubious.

No ribs on stock PL cordsets Mark...

 

[MarkWComer]

No ribs on stock PL cordsets Mark...

Mine has them, but both are Series Two units if that’s the distinction…

 

[mlucitt]

That was before polarized plugs existed...

The earliest National Electric Code (NEC) that I can find that references polarized receptacles is the 1962 edition, which required outlets to be polarized. But it takes a long time for these changes to be widely instituted and they are almost never require updating of installed equipment (outlets), especially in Washington state.

 

[Gepetto]

Mine has them, but both are Series Two units if that’s the distinction…

The bean counters got a better deal on that run of line cords by that time Mark