Status of my science fair project so far (written February 7, 2000)
January 8, 2000: Ordered tubes and audio transformers from Antique Electronic Supply. Cost: $65.34. I expect them to arrive in 5 to 7 days.
January 10, 2000: Back in shop. Designed chassis and brought plans to Metal Fabrications. Should be done by next week.
January 11, 2000: Bought two power transformers and ordered 5 watt 20 ohm potentiometer from Radio Shack. Cost: $25.
January 12, 2000: Parts shipped from Antique Electronic Supply (according to the invoice).
January 14, 2000: Still waiting for parts. Started search for vacuum tube with bright filament in shop. Nothing found. Made inquiry on newsgroup rec.audio.tubes. Someone has offered to send me a weak 811A tube with a bright filament.
January 15, 2000: The parts wonít ship on the weekend, so I expect them Monday (a holiday though), Tuesday or Wednesday. I agreed to the tube offer.
January 16, 2000: The man responded he will ship them next week. Next week is academic week, so I have a week to spare.
January 18, 2000: I visited Metal Fabrications to check the progress of my chassis twice. First time around, they accidentally riveted the bottom lip to the top of the case. I told them how to fix it, but there must have been a misunderstanding, because when I returned later, they had removed the top completely. They said it will be done by the end of the week.
January 19, 2000: The parts from Antique Electronics Supply have finally arrived via UPS Ground. Everything came in one piece, although I underestimated the shipping. Even so, I also overestimated the cost, so I only owe 30 cents. Shipping took 5 business days, as promised. I hope the chassis is finished by next shop week.
January 21, 2000: They made me another chassis, but it is bent out of shape, and it is unusable. The teacher in Metal Fabrications said theyíll build it next week.
January 22, 2000: After my inquiring on when he shipped it, the man replied that he was out of town the previous week and shipped it today. He expects it to arrive Tuesday or Wednesday.
January 24, 2000: Got back to shop today. The chassis wasnít ready yet, but I used the bent chassis to plan the layout. As soon as I get the new chassis, Iíll install the parts. Finding the smaller parts proved to be quite a challenge. The hardest parts to find were a 330 ohm 5 watt resistor and two 100 microfarad 250 volt capacitors. I could not find an exact resistor, so I am going to use a 300 ohm 5 watt resistor and a 30 ohm 10 watt resistor in series. For the capacitor, I couldnít find two 100 microfarad capacitors of that high of a voltage rating, so I am going to use an old NOS multisection electrolytic capacitor that has three 100 microfarad 350 volt sections. I just hope it doesnít leak.
January 26, 2000: Yesterday was a snow day, so I have a day less to do it. The new chassis didnít come until around 1:30. During that time, I scanned the pages into a computer and saved them in GIF (?) format. As soon as I can get a floppy disk, Iíll transfer them to my home computer and post them on the Internet (as well as an enlarged drawing I did using MS Paint). I will begin construction tomorrow. No tube yet.
January 27, 2000: The tube still hasnít arrived yet. I began building it today. First, I drilled the 28 holes necessary to mount the above-chassis parts (Iíll have to drill more for the below-chassis parts), as well as using a chassis punch for nine of the holes. I installed the capacitor can mounting plate, the tube sockets and the potentiometer. Tomorrow, after mounting the below-chassis parts (resistors, rectifier, etc.), Iíll mount the above-chassis parts. If I finish the amp (hopefully), I will carefully test it and hope for the best. Otherwise, I will work on it at home.
January 28, 2000: I continued building it today. I drilled the holes for and mounted the under-chassis parts (resistors, rectifier, etc.). I attached wires to all of the tube socket pins (except pin 5, since pin 2 can be used instead). I mounted most of the above and below chassis parts (except the large power resistor), but I have only started to wire them together. I accidentally drilled a too-large hole for the power cord, so Iím putting a pilot lamp in its place (on the back, mind you). Unfortunately, I did not finish it today, so construction will resume next week if I can get out of class. I also have to drill holes for the power cord, line fuse (if I donít use a pigtail type), and the input/output binding posts. Even so, I attached all the above and almost all of the below chassis parts, and it looks terrific (if you donít mind the rats nest of wires there, but theyíll be gone once I start point-to-point wiring).
January 29, 2000: The 811A tube came in the mail today, along with a socket. I screwed the socket to a block of wood (cracking it slightly in the process, but itís still largely intact). I bought a pair of 6 volt lantern batteries and wired them in parallel for more current (the tube draws 4 amps, and I donít have a power supply that large). The tube filament glows as bright as a nightlight when I connect it to the batteries. Quite a nice effect coming from a tube. It will make an interesting display, although I want to buy a filament transformer for it afterwards so I donít have to buy a lot of batteries.
February 1, 2000: I planned to continue working on my amp yesterday, but snow in Shirley canceled school for me. I tried to work today, but the shop was being cleaned for the 8th grade tours happening tomorrow. I am going to bring the amp home and work on it there.
February 2, 2000: I got quite a bit of work done on the amp today. I wired almost all of the components. All I have left is drilling and mounting parts.
February 4, 2000: I have finally finished drilling and mounting parts. When I tested the amp however, it doesnít amplify signals at all. I will have to bring it back into electronics to fix it.
February 6, 2000: Through conversations through e-mails with people on the newsgroup rec.audio.tubes, and I have come to better understand the voltages. There must be a bad connection somewhere. Iíll have to wait until tomorrow.
February 7, 2000: Got back to shop. I reflowed some solder joints, and bent the solder lugs on the bottom of the tube sockets away from each other. I also connected one of the input terminals to ground. Success! It now amplifies sound. I hastily built a transistor amplifier to compare the tube amplifier to. I invited Todd over, and we listened to the output of both amplifiers, and have determined that tubes sound slightly better than transistors. I also designed a neat display board using color pictures of vacuum tubes which I think looks good. On to the science fairÖ
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