Death by Amp
Tue, 05/07/2013 - 15:14
Hi Greg,
I just got my Kalamazoo Model 2 in the mail. I love it. It sounds great. I'll be sending it to you within the next few weeks for a line out and the basic work. Everybody says to be careful with these old amps. Besides taking a bath with it, how would I go about killing myself with one of these things?
-Taylor
Tue, 05/07/2013 - 21:43
#2
Wow. Lot of great info.
Wow. Lot of great info. I guess I didn't realize that the amp converted the alternating current to direct. Thanks Greg. You're a lifesaver. Haha. I still have the 2 pronged plug. I'll have to get that fixed soon.
Taylor
Hi, Taylor
That's a great question. Most people don't understand that amps actually run on DC "Direct current". DC is even more dangerous than AC when it comes to electric shock. But we're not talking DC like your car - 12V or so. We're talking about voltages as high as 600 volts DC running round your amp. Tubes work on DC.
To make "DC" from AC (that you're getting out of the wall) the amp has to do 3 things. First, a transformer takes the 120VAC line current and turns it into as much as 500-600 volts AC. Then, a "Rectifier" (a tube or a series of diodes) turns that into high voltage DC . This DC is true DC in that the current only flows in one direction - however it still "pulses" as the AC sine wave swells between 0 volts and the top of its wave form. That means a lot of 60 cycle hum - so a series of capacitors are used to filter the DC current and effectively smooth it out into a continuous smooth supply of high voltage DC.
Now - why did I explain all of the above? Certainly when you hear "600 volts" you know better than to reach into the guts of your amp when its on. (Even 120VAC is dangerous and can kill.) But what you might not know is that capacitors act somewhat like batteries. They take on a charge, and they can store it for a long time after you turn your amp off. So just because you unplugged it doesn't mean it is safe. Some amps discharge fully within minutes. Others can hold onto a charge for a day or two. If an amp is malfunctioning, the capacitors can stay charged even longer - several days, even a week.
In normal operation, the amp's covers prevent you from touching these high voltage points - that is, unless you were to remove a tube and stick a piece of metal into the wrong socket hole...... however a malfunctioning amp, particularly one that hasn't been "safed" with a 3-wire grounded power cord - can shock you if you touch anything metal and connected to the chassis. In an ungrounded amp with a malfunction, the chassis of the amp can become "hot" and carry current. Don't forget that the 1/4" plug on your cable is touching that chassis. And the shield inside your cable is connected to that connector. And at the other end its connected to the metal of your mic. Yep - back in the 60's there were a number of deaths - just from touching the mic - or guitar - that was connected to the amp.
OK - the short answer is this. If you don't know what you're doing, don't stick your fingers inside an amp. Ever. Make sure you have your amp serviced by a competent tech. The tech knows how to take precautions such as safely discharging the capacitors before he works on the amp.
/Greg
http://www.blowsmeaway.com