Tuesday, September 16, 2014

A Terrible Compass

DSC05174It’s back to school time and Henry needed a protractor and compass for 6th grade. Felice went to K-Mart and bought a Westcott Two Piece Math Tool Set. It was extremely inexpensive. For some reason the K-Mart page has a weird typo, calling it a “Westcott Clauss Math Set Protractor and Compass”.Even weirder, the combo is not listed on the Westcott website, as far as I can see. Unfortunately the compass is an utter piece of garbage. The video below shows the problem…  


Yes, the pencil clamp is defective. Maybe it is only defective on this one compass, however if you look at the amazon reviews for the compass (not as part of the set), there are a ton of negative reviews.

DSC05189It doesn’t look that bad…DSC05188 Oh, look at how the graduations are already rubbing off.DSC05187 I guess it would be harder to stab someone with it than the old needle pointed ones.DSC05176The clamp mechanism.DSC05178The protrusions on the lever push against the ears on the pencil clamp, locking the pencil in place. At least it does in an alternate universe.DSC05182Without the pencil in place. You can see that the clamping action is slight. The pencil is .287” in diameter (major diameter of the hexagon) and when empty the bore of the pencil clamp, with lever engaged, is .286”. This is clearly not enough adjustment.DSC05177It’s flimsy too.DSC05184I added successive strips of paper between the lever and the clamp.DSC05186Ultimately .020” thickness of paper, on both sides of the clamp (so .040” total) resulted in a firm clamping action around the pencil.

What irritates me is that it shouldn’t be hard to make a compass that works for the same or slightly higher price. I wonder how many children are foiled in their geometric endeavours by such a shoddily made instrument.

Thursday, September 11, 2014

Channel Master 6520 AM Radio

DSCF3052Picked this up at a yard sale last weekend, for $5.00 (half off…)DSCF3055DSCF3057 DSCF3058 DSCF3059 DSCF3060 DSCF3061 This is the only really exciting thing, the battery compartment.DSCF3065 Batteries are held in a tube for easy handling.DSCF3085 Compartment has captured screws that use a coin for a screwdriver.DSCF3070 DSCF3074 DSCF3077 DSCF3079 DSCF3080 Grommets are a bit worn…DSCF3081 Causing the tuning capacitor to cant to the side.DSCF3082 Neat heat sinks on the red headed transistors.

Saturday, August 09, 2014

My New Boombox

Remember the boombox? Well I picked one up at a yard sale today. I’d been looking for a cheap but relatively good quality one for a while so that I could play content from my MP3 player or tablet while in the shower.

The one hitch? It didn’t have an auxiliary or CD input. So I did a Google search for “convert boombox mp3” (not in quotes…) and found a few good sites. The one that had the best advice was this guide to “Installing an Auxiliary input on any Stereo”. The basic technique is to find the input to the amplifier and graft the auxiliary input to it while disconnecting the other inputs. DSCF2974 I cracked it open. Quick tip: first remove every knob you can, then remove the screws and it should come apart easily.DSCF2975 This is my candidate for getting the sound in. That’s the radio board. I’ll snip those wires (the boombox will not have radio or cassette function because it’ll be a pain to keep those as well.)DSCF2976 The cassette assembly also needs some trimming.DSCF2977 I removed the whole motor assembly on the left and the majority of the gears, belts, etc.DSCF2979 The aerial clamp isn’t needed.DSCF2980 The power (L) and speaker (R) connectors.DSCF2983 Now I try and figure out what those 5 wires from the radio board are.DSCF2986 Yay, ground.DSCF2987 And a 5V DC line. It will be removed from the connector.DSCF2989 Ground and stereo left and right hooked into a 1/8” audio cable for testing.DSCF2991 I could just reassemble it without the other two boards but will need them for cosmetic reasons.DSCF2994 Some splicing, soldering and insulating of a new 1/8” cable to amplifier board cable.DSCF2997 After getting it all back together (with neither the cassette or radio board hooked up, but in place) I was able to play some tunes from my MP3 player.DSCF2999 I can stow the cord in the cassette tray.DSCF3001 And it pops open for use.

Wednesday, July 09, 2014

Heathkit VC-2 Voltage Calibrator

I picked this up at OSU last winter, finally got around to checking it out a bit. I’m not really sure what this is specifically useful for. It outputs a square wave of a settable voltage. I’d love a scan of the manual as I haven’t found one on the internet.DSCF2694 DSCF2695 Benny the Beaver.DSCF2697 The peak volts scale is obscured by a replacement graduated dial.DSCF2699 DSCF2700 Set up on the bench.DSCF2704 DSCF2705 4.26V when set to 4V…DSCF2707 DSCF2708 9.36V when set to 8. I’m guessing that the dial is not graduated correctly. Why is it there then? Who knows.DSCF2710 DSCF2713 DSCF2714 An internal potentiometer.DSCF2716 DSCF2719 The internals are typically simple and beautiful for the age.DSCF2724 Removed the aftermarket dial face. Have to give it to my friend SpudDSCF2725 DSCF2726 With the dial removed it seems more accurate?DSCF2728 DSCF2729 Almost spot on…DSCF2731DSCF2730  Not so much at the .1V multipler,DSCF2732 DSCF2733 Nor at the 10x multipler at 1V(x10=10V)DSCF2735 DSCF2736 At 2Vx10 I get 22.6V, so there’s a pretty consistent extra 2.6~ volts.DSCF2737 DSCF2739 But at 5Vx10, I do get almost 50 volts.
I don’t think this was meant to be a precision reference, although I may be wrong. I could play with the internal potentiometer I suppose. Anyway, a neat thing.