More on Watching out for Imported Vintage Blackface Silverface Amps

 
On the old vintage Fender amps as I mentioned earlier there is no earth and only a two pin plug which should be replaced with a cable that supplies a ground to the metal chassis.

Also on the back of valve  ( tube ) vintage fender amps that says ground. What this switch does is switch a 0.01uF on some models or a 0.047uF , capacitor and connect it either to the live or the neutral side of the incoming 120 Volts AC.

What  it is supposed to do is bypass any higher frequency noise coming in from the power line  on either the live side or the neutral side down to earth so that any annoying noise that is on the powerline does not end up as noise coming out of the amplifier.

The issue is that this capacitor with time can leak and allow the AC to go striaght to the chassis. Worst case it can go partially short  circuit and put the line voltage straight onto the chassis !  This will certainly make you playing more “flashy ” as you go up in cloud of blue smoke and yiou are thrown across the room. With a total short circuit in this capacitor, the fuse will blow.  This is one area to look at before deciding the power transformer is dead. It may just be this $1 capacitor that has gone. The easy way to find out, is to disconnect it and then see if the fuse still blows.
I have not checked all blackface amps but I know for certain it is on most blackface and silver face models up till 1978. The smallest amps such as the Champ dont have the ground switch
At the very least replace it  if this has not been done in the last few years. An alternative, is to dis-connect it and provide the power via an extension socket which has line filtering in. These are usually used for computers and are easy  to fnd.
if you choose to replace the capacitor  use one  with at least 600 volt rating as seen in the picture above.
Play Safe!