Old amplifier problem

[frusciante89]

Hi everybody, I have a problem with my my 1030...
I bought it used in the US and I immediately changed all the capacitors...
I then got back to my country (Italy) and I decided to change the transistors as well, since the amplifier was making a very strange noise...
I then bought a transformer (200 Watts) In order to adapt the power cord to the Italian plug. I was finally able to switch it on and everything works fine, it sounds very crisp and clear... however there is an annoying charge on the front plate: it's not electrocuting, but you can definitely feel it... I noticed that when the iPod is connected to the auxiliary wire, and I touch at the same time the metal case of the iPod and the front plate, then this effect disappears...
Does anybody have an explanation for this? Could it be because the power cord is only a two way? I was thinking of replacing the power cord with a 3 way and hook the ground prong to the chassis: would it make any difference?
Another thing I can think of is that I made some kind of mistake in the transistors substitution...
What do you suggest?

 

[jacklim]

The problem most probably lies with the quality of the transformer construction. Nothing to do with the other parts changed.

There seems to be an electrical leak across the primary and secondary windings, or between primary winding and the metal core, through inadequate or faulty insulation layers.

You can check this leakage by using a DMM set on a suitable AC voltage range, placing the probes between 1) the secondary conductor and any external earthed wire, and 2) the metal core and any external earthed wire. The metal core is usually fixed to the casing or PCB by a metal frame which is electrically connected to the ground of the amplifier PCB.

If the DMM shows any AC voltage then there is leakage which caused the mild shock you mentioned. It should be around 70-100 VAC.

To solve the problem you can attempt to use a 3 core cable and connect the 3rd wire (green) to the electrical ground of the amplifier. Or change the transformer.