I really don't know anything about electrical stuff, but the amp has a 2 prong power cord, then a ground switch. what could potentially happen if I didn't replace it?
Adam, you shouldn't get a nasty shock with a 2 wire cord. Despite the implications of all the tips to the contrary, people were not electrocuting themselves daily before the 3 wire cord was adopted!:smile:
This is the REAL story!
There are 2 different categories of power systems in old radios, amps and other vintage gear. Really cheap stuff did not have a power transformer. The line voltage was rectified into DC power for the tubes directly. All circuits must have a ground return. With the cheap gear the chassis was NEVER connected DIRECTLY to the line voltage "ground"! The circuit may have used the chassis as a return but then they used a big capacitor to connect to the AC power as a ground return.
If you had a cheap radio and one of the knobs had broken you might have been turning the radio volume by gripping the bare shaft of the pot, which of course was grounded to the chassis. That chassis was grounded to the circuit through a capacitor, as I had said. One of the two line power lines was always "neutral", or grounded already. The other was "hot" with respect to ground. If you were washing dishes at a metal grounded sink and reached up to adjust that bare volume shaft you had a 50:50 chance that you might get a little tingle shock and NOT a total electrocuting zap!
That's because it depends on which pins on the plug at the wall were lined up with the power line neutral. If things were the wrong way then yes, the chassis was "hot" to ground but THROUGH A BLOCKING CAPACITOR! That capacitor was only big enough to allow signal ground currents to flow through it. Big scary currents saw the cap as a big limiting resistor, that let enough through to give a bit of a "tingle" (not pleasant but not really dangerous) but not enough to be life-threatening.
More expensive equipment had a power transformer. This provides total isolation between the unit and it's chassis and the wiring in the wall.
So far I've been talking only about safety concerns. The other factor is grounding as shielding from stray hum and noise pickup. Using a cap and/or a transformer for isolation still leaves the problem that hum can get into your amp or radio circuits and end up in the speaker audio. If the chassis is grounded through a cap and/or coupled through a power supply transformer then the metal of the chassis acts as a shield to keep that nasty stuff out. However, if the plug pins are reversed so that the "ground" side is on the "hot" wire and not the ground neutral then the chassis is not grounded through the power line system and rather than acting as a shield it actually becomes an antenna for hum! Every guitar player has found that at times his guitar and cord seems to be picking up hum, changing as he moves around.
Every radio owner in the old days knew that his radio,record player or amp would have less hum if he flipped the plug at the wall the right way. With guitar amps the makers put in a "ground reverse" switch. It worked by grounding the chassis to the power lines through a capacitor, but the switch would toggle from one power wire to the other. That way if the plug was the wrong way or if the wiring in the wall was not consistent ('cuz someone let their idiot brother-in-law do the wiring) the switch would flip things for you and let you choose the position that killed the hum best.
Where the scary stories come in is that the only safety feature was the quality of that blocking capacitor. It came to be known as the "death cap" because if it shorted then you DID have a 50:50 chance that the plug would be inserted in such a way that the "hot" side of the power line would appear on the chassis of the unit! If you stood on something grounded and touched the metal chassis of the unit then you would get the full force of the power mains flowing through you! This hurts and in some cases can even kill.
"Death cap" shorts were relatively rare. Manufacturers knew that even though the system was legal nobody would want to buy a unit with a reputation for shocking the customers so they used good quality capacitors. Besides, the law through electrical wiring codes said they HAD to! Failures were rare and odds were 99% that nobody got killed! They just got a bad shock that caused them to say some naughty words and then took the unit to the repairman.
The 3 wire system just added a common ground wire to everything. The extra prong on a power cord is connected to an actual grounded wire in the wiring system in the walls of your house. This prong is also connected to chassis ground in your amp. If something ever did go wrong inside your amp then the hot wire would be grounded if it wound up connected to the chassis. This would immediately blow the fuse!
The best use of 3-wire cords is with power tools. Who wants to use a power drill on a damp construction site when the metal housing has developed a short to the power line?
So don't worry, be happy! I would get the cord changed but wait until you're paying a tech to open the amp up anyway. The extra time to change the cord will be less, which means a smaller bill.
The change is a good idea but the danger is nowhere near as high as some folks have been suggesting. Still, people do win lotteries and they do get struck by lightning. That's why I'm NOT saying don't bother! Just don't lose any sleep if it's not changed by tomorrow...:smile:
:food-smiley-004:
