atomic_fungus (atomic_fungus) wrote,

#3303: First rehearsal for me

And boy are my arms tired!

Having had a first run through the script for real, I can say it doesn't look too too difficult for me to handle. There is an additional solo (so I've got two). I didn't know about the second one because it just says "SOLO 2" in the script, and the CD has a kid singing that part in that song rather than "Dad".

Still, not too shabby for my first rehearsal. Seems like it'll do.

* * *

A month ago, having gotten my fiber optic "UFO" lamp cleaned up and working again, I had a hankering to also plug the plasma globe in and get it working, too. I can't remember why I stopped using my accent lights (except--of course--that I simply had nothing else to worry about) but I bought the damn things for a reason, after all.

Anyway, the fiber optic lamp was pretty easy despite the extreme festoon of cobwebs it had. I washed it off in the kitchen sink, then ran a comb through it to re-separate the strands. It's fine.

But then again, its power supply had remained plugged into it all this time. Not so with the plasma globe; I couldn't find the wall wart for it.

The label on the bottom says "12 V AC" and all the wall warts I found were 12 V DC. Now, I knew that I hadn't put the lamp on the top shelf and buried its power supply somewhere in the nethermost reaches of the basement, but I simply could not find the damn thing.

It occurred to me that--hey!--I've got a bachelor's degree in electronics and am therefore qualified to build a 12 V AC power supply. I've done it before, and as far as I know the thing is still working. (I wish I knew where it was. It was for a very cheap stereo amplifier I bought from a surplus store, and that thing was pretty cool.)

But then I thought, "Maybe I ought to crack open the case on the thing and see what the circuit looks like, first." You see, you rarely see AC wall warts; they're almost always DC. Maybe the label was put on by a maniac or something. But high voltage devices like a plasma globe are generally AC devices, just because of the physics of the circuitry. Still, the thing's far too light to have any kind of big transformer in it.

Last night I finally got around to it, and pulled the bottom off; and lo and behold, what did I see, but four diodes of exactly the same type in a neat array right next to where the power wires went into the circuit board. Do you know what that means?

It means bridge rectifier, that's what it means. 99 times out of 100 if you have power wires -> four identical diodes right next to each other in a neat array, you're taking AC and making it into (admittedly lumpy) DC.

And since this was made to be an extra-cheap $20 accent lamp, there's no way the guys who designed it would use a dedicated bridge rectifier part for $0.05 each when they could use four 1N400 diodes for $0.005 each.

(And I am probably overestimating the per-diode cost of 1N400 diodes in bulk.)

So I put the bottom plate back on, grabbed a 12 V DC power supply, plugged it in, and tried it out, ready to yank the cord if the thing did anything other than power up normally. Well, it powered up normally, and my plasma globe now works again. Whee!

So now, every so often, I stop what I'm doing, touch the globe, and make "electrocution" noises.

* * *

Vox Day: "Feminism is a failure."

Scientific study suggests that plainer women are more likely to be career-oriented.

Same vein: The Feminist War on Men.

* * *

Karl Denninger has a really good pro-2nd Amendment rant today.

* * *

Here's a list of "the top 10 overrated songs of all time".

I'll save you the suspense: "Imagine" is #1. As it should be:
There are no words for how truly evil and terrible this song is; Kurt Schlichter has done a masterful job of epically fisking this small shard of utter and complete rubbish. First, the aesthetics. It begins with some pretentious piano chords to set the mood: this will be a deep song. Lennon sings it in cloyingly whiny fashion, like a schoolgirl who has discovered that there are starving people in Africa for the first time. It’s vomit-inducing bad. And the music itself is not just unspectacular, it’s blasé. It commits the worst musical sin: it is completely boring.

But that’s not what makes this song so horrible. For that, we have to examine the lyrics, which are not just ignorant, but Soviet-style ignorant. It’s a communist, atheist song, pure and simple.
This is 100% accurate. (Possibly 150%.)

Bob Dylan's "Like a Rolling Stone" is #2. One reason is that Dylan "...sings like a cat being run over by a nail-studded steamroller."

And #9 is a song by U2. "U2 is second only to The Beatles in the pantheon of overrated bands. Pretentious, whiny, boring." Annoying. Yeah.

I'd argue with #7, "Born to Run" by Bruce Springsteen. Not because I like that song, but because Springsteen's "Born in the USA" is much worse. Six chords on the keyboard, over and over and over and over again; it's not a song so much as it's a lead-in that old Bruce contorted way out of shape.

"Stairway to Heaven"--I do like that one, though I rarely listen to it because it's best taken in small doses. I'd replace that with...

Queen's "Bohemian Rhapsody". After hearing it at Target every work night for three months I am sick almost to puking of hearing it. Even now, three years after I lost that job. Yeah. It's an okay song. It's fine to hear once in a while (or was before I was unwillingly overdosed on the entire run of Queen's "greatest hits") but it's just not that good a song even when you factor in that Freddie Mercury tragically died of AIDS and Rock And Roll Will Never Be The Same. *sigh*

I've never really liked Queen all that much anyway, but if I had to pick their best song "Bohemian Rhapsody" would not have been it even before I was made thoroughly sick of it.

* * *

Another neat thing about the plasma globe: I have a "circuit tester" for AC applications which consists of a couple test leads and a neon bulb. It's a cheap electro-gewgaw which is useful for checking to see if there's AC present in the wall socket when something doesn't power up, and I don't even know where I got it.

Anyway, if you hold one lead between two fingers and touch the other one to the plasma globe, the neon lights up. There is a fair amount of voltage present at the surface of the plasma globe--but virtually no current, which is why you can touch the thing without barbequing yourself.

Having had the thing open, I saw that the circuit board is mostly cheap electronics with a very inexpensive flyback transformer (from a tube-type television set) for the HV part of the circuit. A typical flyback transformer generates tens of thousands of volts; it's part of how the electrons are accelerated towards the screen in a picture tube. A picture tube is essentially a gigantic capacitor, which is why there were all those warning stickers plastered on the inside of TV cases and on the picture tube yourself--a picture tube can store a hell of a charge, and the bigger it is the more charge it can hold. More than enough to kill you dead, even in a TV with a 12" screen.

Current is what kills you, not voltage; and when you short a capacitor the current flow is arbitrarily high. According to theory the current is infinite. In practice it's just "fucking high" because practical components have resistance, however small. But if you short that picture tube across your heart, the current will be high enough to stop your heart, because it only takes 10-20 milliamps or so to do it.

Now, you can touch a D cell battery with one hand on each terminal--despite its rated output of about 300 milliamps--because your skin has resistance. Get a DMM and hold one probe in each hand, and you find that there's perhaps 10 megaohms across your body; at 1.5 VDC that makes for a current of 150 nanoamps.

Put that D cell into a battery holder, and then jab one terminal wire into one thumb and the other into the other thumb, far enough to bleed--you're risking death.

High voltage is a problem because every substance has a dielectric constant, a voltage below which current either does not flow or faces high resistance. At 20,000 volts, the resistance of human skin just stops mattering; you ground out a few microfarads of capacitance at 20,000 V and there'll be enough current flowing to kill you.

So: the circuit tester reports that there's a significant voltage at the surface of the plasma globe, yet of course you feel nothing when you touch it because there's virtually no current flowing. Glass is an insulator; it can be charged but it can't conduct.

Plasma Globe entry at Wikipedia if you really want to know more about how the thing works.

Apparently a typical operating voltage for one of these things is about 3,000 V, but the current alternates at around 35 kHz. Hence the flyback transformer, for which such a frequency is typical.

You really have to know what you're doing with high frequency high voltage if you want build your own. Okay? I wouldn't try to build my own, even though it'd be cool--that's how much HV-AC knowledge and experience you need if you don't want to fry yourself or burn down your house. (Caution: that site is entirely white text on dark blue background; it's very hard on the eyes.)

And yes, after the thing has been running a while, you can smell the ozone.

* * *

As for me, I managed about 2 hours of sleep last night. I don't even know why; I felt fine. No anxiety, no nervousness, no nothin'; I was tired after 2 AM and went to bed...yet I couldn't sleep.

Maybe I was just excited for my first rehearsal today, I don't know. What I do know is that I'm going to go lay down and take a nap for a few hours.
  • Post a new comment

    Error

    default userpic

    Your reply will be screened

    Your IP address will be recorded 

  • 0 comments