Category: electronics

My Marshall amp has been sitting unused for a long time because it doesn’t make any noise. Recently I’ve been wanting to get it going again so that I can play electric guitar from my couch instead of walking all the way downstairs (i.e. ten feet). Any old amp will do this task as I can use my POD for effects. But I have the Marshall so why not put it to use? Incidentally, I can just connect the speakers directly to the POD’s headphone amp, but that’s no fun.

Vacuum tubes are notorious for being flakey, so I figured a new set of tubes might make it work again. I ordered a new set, plugged em in, no go. The power tubes heat up but the preamp tubes do nothing. That’s about the extent of my expertise on amplifier repair, so the only other thing I can do is open it up and look for cold solder joints or blown fuses. Alas, I found nothing obvious when I did this.

Working on any high power AC gear is dangerous. In fact, today while discussing my broken amp with a coworker, I said that despite my many hours logged in EE labs in school, I was not at all comfortable working on it myself. Perhaps I should have listened to me.

I was smart enough to unplug the amp, and careful enough to keep a hand in a pocket. But still, I was sloppy when putting it back together and managed to discharge a high voltage cap with my fingers. Holy hell that hurts! I dropped back a couple of feet and let out a loud scream. Youch. I will not be doing that again anytime soon. Luckily, I don’t have any permanent damage: I got a tiny electrical burn on my middle finger (that probably would be worse if I didn’t already have a half-inch callus on it from playing guitar). And I earned a healthy fear of high powered electronics.

So, people of the internet, don’t do what Donny Don’t does. Discharge those caps!

You pretty much have to buy vacuum tubes from the third world or eastern bloc these days since they aren’t much in demand over here. The ones I bought were all Sovteks. I love the Soviet iconography on the box:

Saturday, I deconstructed a broken CD-ROM to make a toy. This is essentially a so-called “symet,” which is the simplest device in the BEAM robotics world. Usually, they are made with solar cells and the accompanying logic, but as I don’t have any of those, I just used a AA battery. One battery, a motor pilfered from the aforementioned CD player, and some vacuum tubes glued on for balance (they serve no electrical purpose; I just had them sitting around and they look cool). Pretty simple but more fun than a box of Transformers. Possibly.

This is what the inside of a 1st gen CD-ROM looks like:

This is what the inside of my MP3 player looks like:

I spent a few hours yesterday doing the house-wiring thing. Again. I’m running cable for HDTV from my attic to my living room. Therefore I have little pink bits of fiberglass insulation everywhere. I have the cable running the whole distance to the TV but I had to stop short of getting it actually into the living room. It appears that I will need to reopen the hole in the wall from last time to drill a new hole through the stud to let the cable up from the crawl space. And then patch and repaint. Why am I doing this again?

In the district the other day I saw a jeep with spinners on the spare. Awesome, dude! I bet that guy has 20″ rims if-you-know-what-I-mean.

As a consumer of all types of liquids sold by heartless multinationals, I discovered this week that a plastic Evian bottle cap mates perfectly with a Coke bottle cap to make a little enclosure. It occurred to me immediately, nerd that I am, that this would make a good project box for any really small electronics project. Not having any such projects in mind, I decided I would make something simple and useless, and what’s more useless than a flashing LED?

The circuit for a blinking light is pretty straightforward – it’s just a timer chip with an LED on the output. Except for the batteries (I used two 3V watch batteries taped together), I happened to have all the parts on hand: a 555 Timer chip (from a red box that I never built), 3 resistors, a capacitor, an LED, wires and some perfboard. This site has more info if you want to build your own. I just picked my own combination of resistors and cap that had a frequency around 2 Hz, then proceeded to do one of the worst soldering jobs ever, then cut up the perfboard so that it fits nice and snug inside the bottle cap. Now, I think it is time to listen to some Floyd.

A long time ago, I lost my way. And by “way” I mean “the F-connector die set for my racheting crimper.” That thing is impossible to find. I’m trying to locate it because I just got a large new aerial TV antenna so that I can get more hi-def channels (for a mere $25 – don’t waste your money on the $100 ones at BB or CC). I plan to mount the monstrousity of aluminum in my attic and connect it via RG-6 running through the same path in the walls that my cat-5 cables take. This will be a bit more challenging the second time around since the holes in the walls cut for that purpose are now all sealed up. Anyway, last night, unable to make a 100′ cable without the crimper, I assembled the antenna in my living room and connected it via some short coax I had around, and the results are fantastic. Before, I could barely receive FOX and get nothing else; now I get all the networks, mHz, and PBS in glorious digital picture and 5.1 sound. Hooray for the electromagnetic spectrum! WB still doesn’t come in, as if I watch that anyway. Maybe this weekend I’ll get it all setup in mythtv so that when I record, say, the mind-enhancing television show 24, mythtv uses the HD card instead of cable.

(Kill your TV.)

Lately I’ve been consumed with an urge to build things. Call it a manic phase. So last night I indulged, armed with my newest power tool: a Dremel. 35000 RPMs of pure madness. When I have it in my hands, you’d be well advised to stand back ten feet.

Okay, I know case modding is the geek equivalent of spoilers and ground effects. All the same, it is nice to add a little bit of personal touch, however slight, to one’s homegrown Tivo replacement. Since my newly-acquired LCD module didn’t fit in my case, I knew I’d have to do a little bit of surgery.

Obstacle number one is that the hard drives bump right up against the location where the LCD would have to go (there is already a display window that for some reason was placed there). I took the hard drive cage out, and moved the hard drives to the 5.25″ bays with mounting brackets. My ZIP drive occupying one of those spots got the boot. This was a bit of a tight fit because there are front panel USB and firewire connectors on the case that intrude into the bottom-most drive bay, but with some better cable routing and by mounting the harddrive a little high, I squeezed it all in there.

Obstacle number two is that the existing opening for the LCD is nowhere near big enough for this module. I had originally considered making a hole large enough for the entire PCB assembly and mounting the LCD from the front, but then I decided it would be sufficient to just widen the existing hole and mount the PCB assembly to the inside of the case. The latter scenario allows me to fall back to reinserting the hard drive cage if I ever decided that was needed, whereas the former would have me taking out the cage’s mounting screw terminals. So I put the metal cutter on the Dremel and cut out a larger square from the case. There’s something industrially visceral about the shower of sparks and taste of toxic paint accompanying this process. With a little fine tuning and some sanding of the edges, I had a perfect matched opening in the case for the LCD.

In order to mount the module, I picked up a piece of perfboard from Radio Shack that I drilled appropriately to attach to existing screws on the PCB. Then I screwed the perfboard to existing mounting holes inside the case. The results? Quite nice. The window glass in the case, unfortunately, is tinted, making the LCD difficult to read at a distance, but it still looks good up close. Mythtv is already built to display the program information and progress as you watch TV, and menu items as you navigate with the remote. Probably not worth all the work and cost, but what else did I have to do?

More pictures in the gallery.

This is going in my mythtv box. I used to have a VFD there but it didn’t work well with lcdproc and the parallel interface required running a cable out of the back of the unit to connect to the parallel port. Very ghetto. This module has a USB interface so I can run it directly to the appropriate motherboard headers. The fun part is just beginning though: while the module matches the case’s display window perfectly, it is too thick to be mounted in the space between the hard drives and the front panel. So I’m going to have to really mod the case – relocate the hard drives elsewhere, and poke a bigger hole in the front. Oh well, at least it’s an excuse to buy a Dremel.

Mythtv now has nice support for LCDs built-in. I’ll try and put up a couple of pictures when I get it all together.

One of the products of Saturday’s spending spree arrived last night: a midrange Denon 7.1 home theater receiver. I think the power supply in my old Aiwa is about to give up the ghost, as the display has dimmed significantly, and the system turned itself off on me once or twice. Also it never really delivered enough power to my speakers in the first place. The new one, though… it’s like I have a whole new HT setup. One really nice feature of this unit is that it comes with a microphone that you place at your listening location, and the amp automatically calibrates the speaker levels and delays. Much more accurate than my previous adjustments by ear, and much less work than the tripod and meter approach favored by Welsh. Unlike all of the other consumer electronics gear I’ve purchased in the past, this one will finally grant me happiness and personal fulfillment.

I’m going to try to freecycle the old amp (unless anyone else I know wants it). No sense in contaminating some third world water supply with electronic waste.