[Wayner]

Oneinthepipe,

If you look at a 120volt outlet, you will see 2 vertical slots over a mouse hole. The slot on the right (the smaller one),  is "hot" or L1, (it is common practice to turn GFCI outlets upside down so the ground mouse hole is on top). The larger slot is neutral. With 2 or 3 prong equipment (2 prong non-grounded) the wiring must be correct. In Franks equipment, the hot or L1 goes right into a fuse. If the wiring of the IEC-14 socket has the 2 plugs reversed, then the neutral goes into the fuse leaving the L1 unguarded. This is very bad.

AC and DC have a similarity in which L1 for both instances gets the circuit completed with a neutral or common (in the case of DC). The only real difference is that AC has a 60 cycle per second wave changing from a 60 volt plus value to a 60 volt minus value.

If you were to take L1 and touch neutral or common, you will have a completed circuit. If you connect L1 to ground, you will have a completed circuit. If you connect Neutral to L1 you will have a completed circuit. If you connect neutral to ground, you will have nothing. (Sorry to be simple, just to make it clear).

Wayner

[oneinthepipe]

Wayner:

Thank you.  I have a basic understanding of the layout of the outlet and plug wiring.  The outlets in my house for audio equipment are 20A dedicated circuits with isolated ground outlets.  My issue is that a previous owner (not the immediate prior owner, who has installed several AVA amp and pre-amp mods) of my recently acquired Super 70i installed a grounded three-prong outlet.  The ground prong wire (mouse hole) is connected to the chassis.  The neutral (left) prong of the power cord is connected to a power transformer lead by way of a terminal strip.  The hot (right) prong is connected to lug 2 of the on/off switch.  There is a jumper from lug 1 of the on/off switch to lug B of the fuse post, and the other power transformer lead is connected to lug A of the fuse post. 

L1 is connected to the 1) switch, 2) fuse, and 3) power transformer lead.  The fuse is a 3A slow blow.  In modern equipment, I believe that a fast blow fuse would be used before the switch.  I can easily insert a fast blow fuse inline in L1 before the switch.

I should ask this question.  Are the power transformer leads on an ST-70 polarized to hot and neutral?   I didn't believe that they were, although I didn't measure either of them to ground with an ohm meter, but I must be missing something, because this otherwise seems fairly simple. 

I think that I will purchase a book about tube amps.  I owned an ST-70 many years ago, but I honestly can't remember much about it. 

The unit seems to work fine, but the advise on this site, generally, is to avoid grounded power cables.