[Boatanchors] Reminiscing, my 8th Grade Science Fair Project

Sat Apr 16 18:32:22 EDT 2016

Great story, Phil! Science fairs were always fun. The first time I entered in one, was probably first grade. My father helped me rig up a little electric motor to an ammeter, so when you spun the motor's shaft, the meter pointer would go up. Kinda cheesy, but it looked neat mounted to a wooden board. Some time after that, my parents got me some of those Radio Shack "Science Fair" project kits with 130 or 200 circuits to build (not really a science fair, but it was in the name! hihi)

By the time I got to high school, the science fair was mandatory for sophomores and juniors, and optional for seniors. For 10th grade, another student and I did a simple project on carbon-zinc vs. alkaline batteries and how long it took for each one to be drained below a usable level. Used a power resistor for simulated loads, and a portable CD player for actual loads (IIRC, the carbon-zinc batteries didn't even have enough juice to power up the CD player). The teacher wasn't crazy about it, and we didn't get too great a grade on it.

I knew we had to step it up for next year. Going through a bunch of old electronics magazines at the back of the electronics shop, I found an article in the January 1995 issue of Popular Electronics on how to build a tube amplifier. It was a very simple design, using two 60FX5 tubes in push-pull with an input transformer to drive them (no phase inverter). I decided that we'd compare tubes vs. solid-state amplification (back when tubes were just starting to come back into vogue with the audiophiles/phools), and this tube amp would be just the ticket. For a solid-state amp, I'd build a simple TIP-31/32 design, assembled on a breadboard.

Thanks to my parents, I was able to order the needed parts from Antique Electronic Supply (no repair shops to speak of in my area to use as sources, and the school's electronics shop didn't really have much in the way of suitable tube-type transformers lying around). The amp shown in the article was built in breadboard form, but on the recommendation of the instructors in the electronics shop, I decided to build it 'the old-fashioned way' using a metal chassis (took a few attempts for the metal fab shop to get it right). Building the amp took about a week, largely in my spare time. Once both amps were built, my friend and I compared the two, and found that while similar, the tube amp sounded a little nicer.

When the fair came up, I went all out. I decorated the presentation board with nice color printouts of vacuum tube pictures, and used my old Macintosh SE to print up a nice dot-matrix banner to put on the wall behind us. A member of the rec.audio.tubes newsgroup provided me with a dud 811A tube, whose filament lit nicely when powered with an old battery charger, to use as a display piece. Unfortunately, the 3W of push-pull pentode had to compete with another student's speaker design project set up nearby, which was driven by some giant SS amp. Even so, the project went over quite nicely with both teachers and the general public, and I got several nice comments from people who looked at it (though some jerk stole the portable CD player I was using as a source on the second day of the show, grrr).

In the end, we got a decent grade, but only managed an honorable mention. The aforementioned speaker project (which looked to me like it was slapped together using random drivers stuck into a box) got second place, with first place going to, of all the things in the world, a pedal-powered wheelchair. Think about it for a moment... Despite the less-than-stellar showing and the theft, it went quite well overall, and planted the seeds for my interest in vacuum tube devices, which continues today. Anyway, here are some links:

Main project page with schematic and info: http://www.electronixandmore.com/adam/tubeamp.html
More construction info with article scans: http://www.electronixandmore.com/adam/tubeamp2.html
Pictures from the science fair: http://www.electronixandmore.com/adam/pics1.html
Journal for the build: http://www.electronixandmore.com/adam/sfjournal1.htm

Hope you enjoyed my story! Sorry about the wall o' text, and the somewhat off-topic-ness.
-Adam

-- 
Adam Vaughn
Collector of old computers, video game systems, radios and other electronic equipment... 
Visit my page at http://www.electronixandmore.com/adam/index.html

On 04/16/16, Phil<ko6bb1 at gmail.com> wrote:

Hi All,

This is a copy of a message I sent to the Regen group.

WAY-WAY back when I was just a young sprout, I wasn't sure what I wanted 
to enter in the "Science Fair" (don't remember if that was the 
'official' name or not).

Well, just about everybody knew that I really had only one interest in 
life (and they weren't girls at that time ;-) In fact, I had trouble 
keeping interested in most of the classes, though I managed to keep from 
bringing home any D's or F's (I'd have had a 'Parental Conference' if I 
had).

The science teacher suggested that I bring something "radio" and 
demonstrate/explain how it worked.

One of the things I thought of was taking my Signal Generator (think it 
was an Eico), a small AA5 receiver, mic and pre-amp and use it all as a 
mini broadcaster. But that was a lot to lug to school on a bicycle, and 
I didn't think it would be a good demo.

Then I looked at a box of parts that I'd scrounged from some junked out 
radios, mostly AA5's. When I parted out something (and I had a good 
source in the local TV/Radio shops), I saved EVERYTHING usable, 
including old resistors, capacitors, tube sockets etc.

Eureka!! I'll build an AA5 (All American 5) receiver. Only problem, 
funds were about non-existent, as was a suitable chassis (the one thing 
I didn't keep from parted out sets were the chassis and cabinet (if it 
had one). Besides, it would be hard to make a suitable display that 
way, it might look like I'd just pulled a radio out of it's cabinet and 
not put any effort into it.

Then an old magazine article extolling the virtues of "breadboarding" 
projects lit up a lightbulb in my head. I needed a breadboard, and I 
knew just where to find one.

Doing a couple uncalled for chores around the house followed by 
sweet-talking mom and I was the proud owner of one of her kitchen 
breadboards (think she was happy to be able to buy a new one anyway ;-) 
It wasn't pretty, but it was functional.

Taking my prize to the garage (which was my bedroom & shop) I gathered 
up all the needed parts, tube sockets, tubes, IF cans, output Xformer, 
tuning cap, speaker and so forth.

I think the only thing I bought was a Ferrite 'loopstick' for the 
antenna. Anybody here remember those? They were a small adjustable 
antenna coil with a short wire on it to act as the antenna. They were 
often touted as a universal replacement for damaged loop antennas. The 
board was too small for the large loop antennas that typically resided 
in the back of old sets.

After the donkey work was completed the real job began, laying out the 
entire collection of 'scrounged junque' in the order of signal flow. I 
don't recall how long it took to assemble all of it, probably about a 
week as I was a very experienced builder by then. . .

The first time I plugged it in I stood back as I wasn't really sure what 
that Frankenstein Monster would do when hit with 110VAC!

SURPRISE, it worked! Only problem is, with no natural chassis shielding 
etc it also oscillated to beat the band. Whistles and squawks like you 
wouldn't believe. But with some careful tweaking and rerouting of some 
wires I got it tamed down and it actually played music.

I then made up little paper labels briefly naming each stage, then 
borrowed mom's typewriter and made up a "poop sheet" describing what 
each stage did.

A couple days or so before the science fair the teacher asked me how it 
was coming. I described it to her and she asked to see it. When she 
saw it she was HORRIFIED that I intended to plug that thing in and 
display it!!! Said if I wanted to enter it AND power it up I had to put 
a safety cover over it (this fits in with a recent discussion we had 
here on AC/DC power)!

To this day I have NO idea where dad got it, but he pulled a magic act 
and brought me a piece of clear plexiglass (or whatever the clear 
plastic of that time was) cut to the proper size to fit over it. A 
couple pieces of wood to cover the front and ends held the cover in place.

I think that was the ONLY time I ever got an "A+" on ANYTHING in school, 
lol.

-- 
73 From "The Beaconeer's Lair"
Phil, KO6BB
http://www.qsl.net/ko6bb/ (Web Page)

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ACC: HOMEBREW LF-MF Pre-Amp, MFJ-993B HF Auto-Tuner.
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