guitargeek

(petulant whining expurgated)



LOUD. AS. HELL.

So I was working in the shop last night, tweaking the circuit in my amplifier. I got ready to try it out so I plugged it in and hit the power to let the tubes warm up, then hit the standby switch and set the bias voltage (it's like setting the idle on your car's carburetor). When you do this kind of project, the workbench gets full of little snippets of wire, blobs of solder and other electrical detritus, so I fired up the ShopVac...

See, there's a problem with the electrical service to the shop. I thought it was a bad run from the pole to the shop, so I dug a trench and laid in a new line, connected it up and still had the same problem. It's a seesaw effect: turn the belt sander on and the voltage on that circuit drops while the voltage on the other circuit goes up...

Well, when I turned on the vacuum cleaner, it pulled the voltage down for that electrical circuit and caused the circuit that my amp was plugged into to spike, which killed my amp.

I did a postmortem and found this:





See where the wrapping is busted on that black 22uf capacitor? These things bulge when they fail, it gives you a visual indication.

I looked in my parts stock and didn't have another cap that size, though I did have one of the same value, just physically larger...




It's funny, those Sprague Atoms cost more and have this air of "mojo" about them... they're supposedly better, but some other amp geek recently cut one open and found that the actual capacitor is the same size as these little black NTE caps, they're just in this huge empty can. That's the power of hype for you! It turns out that Sprague Atoms are a lot like Dairy Queen's ice cream: mostly air.

I'm actually not that upseat about this little mishap. It could have been a LOT worse! If the power spike had munched the power transformer, that would have been $100 to replace. I also shocked the piss out of myself last night: I got in a hurry trying to diagnose the problem because I panicked for a minute. The power transformer puts out 460 volts, and that hurts but it doesn't carry much current so I wasn't burned or killed, so I got to (re)learn a valuable lesson: Don't get in a hurry when you're dealing with electricity. The current flowed over about a half inch of my left forearm. I once took 300 volts across the chest (up one arm and through the heart and down the other arm) years ago when I was starting out. If you survive something like that you learn a few lessons about dealing with that stuff...

This evening I got inside the breaker boxes on the power pole. After dealing with the wasps and their nest, I managed to track down what I think is the problem: it seems that the transformer up on the pole that feeds the shop and garage and the pump for the well is defective... one side puts out 142 volts, while the other side only makes about 106 volts (each side should be making about 120 volts). I'll call the electric co-op tomorrow and see if I can get them out here to look at it. The good news is that I know the problem isn't in my wiring, the bad news is that I should have called the co-op a long time ago, before my Dremel ate itself. And the belt sander. And the other ShopVac. And my amplifier!

Anyway... did you guys know that I've been building a guitar amp?