What are Science Fair® Kits? 
Radio Shack/Tandy didn't merely sell electronics; some of their product range was tailored toward students and hobbyists, fostering learning, experimentation, imagination, and exploration. Beginning in 1969, Radio Shack introduced a series of do-it-yourself experimental kits under the Science Fair® brand, aimed at educating both children and adults in electronics, physics, magnetism, computers, aerospace, and related sciences. For many, these kits served as the catalyst for meaningful careers in various fields. 
In the realm of electronics, Radio Shack offered a variety of xx-in-1 Electronic Project Kits, complete with comprehensive manuals for constructing diverse electronic devices. These devices ranged from crystal radios to strobe lights, audible birds to lie detectors, sound effects generators to sirens, rain detectors to burglar alarms, and color organs to phonograph amplifiers—exciting projects that sparked creativity and ingenuity.   The Radio Shack Science Fair® kits provided all the necessary components to assemble intriguing gadgets such as crystal radios, lie detectors, police monitor radios, shortwave radios, solar-powered devices, adjustable strobe lights, electronic organs, and much more. 

Another popular offering in the 1970s was the assortment of P-Box® Kits, derived from "perf-box," which featured plastic perfboard boxes containing all the electrical components required to build specific electronic devices. Additionally, Radio Shack's Archer® Project-Board® and ArcherKit® projects expanded the array of electronic projects available to the hands-on enthusiast.

This site has THE LARGEST SOURCE of Radio Shack/Tandy Science Fair® Kit Manuals!  If you are missing the manual for your Science Fair® Kit or just want to try some of the cool experiments, all of the manuals below are available for free download.  There is a .pdf download link on the top of the linked pages below.  PAY IT FORWARD:  If you want to help others who have a Science Fair® kit but need the instruction manual,  please contact me if you have a manual to contribute.
** denotes manuals of very low quality, which I hope to replace soon with a better version.  
1-Tube AM Radio Kit 28-100
2-Transistor FM Radio Kit 28-115
3-Transistor Short Wave Radio Kit
5-Transistor AM Radio Kit 28-253
8-Transistor AM Radio Kit 28-222
30-in-1 Electronic Projects Lab
50-in-1 Electronic Project Kit
60-in-1 Electronic Project Lab**
60-in-1 Electronic Project Lab
75-in-1 Electronic Project Kit
100 kHz Frequency Standard Kit
130-in-1 Electronic Project Lab
150-in-1 Electronic Project Kit
160-in-1 Electronic Project Kit**
200-in-1 Electronic Project Kit
AC/DC/OHMS Indicator Kit 28-141
AM Broadcaster Kit 28-209
Aeronautical Lab Kit SFX-4000
AM Short Wave Radio Kit 28-176
AM-VHF Monitor Radio Kit 28-163
Construction Hints (1971)
Crystal Radio Kit 28-207
Digital Computer Kit 28-218
Electronic Computer SF-5000
Electronic Digital Logic Lab 28-226
Electronic Reverb Kit 277-132
Extension Speaker Kit 28-123
Fire Alarm Kit 28-117
FM Wirelesss Microphone 28-109
Globe Patrol Receiver Kit 28-205
Goofy-Lite Kit 28-130
Heads/Tails Game Kit 28-124
Indoor/Outdoor Thermometer Kit
Lie Detector Kit 28-182
Light Operated Alarm Kit 28-128
Metal Locator Kit 28-181
Microcomputer Trainer 28-260
Moisture Detector Kit 28-132
Organ Kit 28-101
"OTL" Audio Amplifier Kit 28-106
Power Supply Kit (Archer) 277-125 
Psycholite Kit 28-171 **
Solar Operated Radio Kit 28-129
Stereo Amplifier Kit 28-113
Telephone Amplifier Kit 28-116
Time Base Generator Kit 277-115
VHF Receiver Kit 28-221
Donations of manuals welcome!
List of Science Fair® Kits
Here is a list of many of the projects kits under the Science Fair® and P-Box® Kit brands:
1-Tube AM Radio Kit 28-100, 2-Transistor FM Radio Kit 28-115, 2-Transistor Radio Kit 28-102, 2-Way Intercom Amplifier Kit 28-127, 3-Transistor Short Wave Radio Kit 28-110, 3-Way Code Oscillator Kit 28-105, 5-Transistor Am Radio Kit 28-253, 8-Transistor Am Radio Kit 28-222, 30-in-1 Electronic Projects Lab 28-161, 50-in-1 Electronic Project Kit 28-201, 60-in-1 Electronic Project Lab 28-256, 60-in-1 Electronic Project Lab 28-261, 75-in-1 Electronic Project Kit 28-247, 100 Khz Frequency Standard Kit 28-140, 130-in-1 Electronic Project Lab 28-259, 150-in-1 Electronic Project Kit 28-248, 160-in-1 Electronic Project Kit 28-598, 200-in-1 Electronic Project Kit 28-249, AC/DC Ohms Indicator Kit 28-141, AC/DC power Supply Kit 28-104, Acid Rain & Water Quality Analyzer 28-142, Aeronautical Lab Kit SFX-4000, AM Broadcaster Kit 28-209, AM Short Wave Radio Kit 28-176, AM VHF Monitor Radio Kit 28-163, Bell/Buzzer Code Key Kit, 28-112, Crystal Radio Kit 28-207, Digital Computer Kit 28-218, Electro-Magnetic Experiment Kit 28-2 2, Electronic Computer Kit 28-180, Electronic Computer SF-5000, Electronic Digital Computer 28-199, Electronic Digital Logic Lab Kit 28-226, Electronic Organ Kit 28-101, Electronic Organ Kit 28-215, Electronic Siren Kit 28-107, Electronic Snap Kit 101 28-286, Electronic Snap Kit 303 28-288, Extension Speaker Kit 28-123, Fire Alarm Kit 28-117, FM Wireless Microphone Kit 28-109, Goofy Lite Kit 28-130, Heads Tails Game 28-124, Indoor Outdoor Thermometer Kit 28-135, Inst-a-Plate (electroplating) Set 28-203, Junior Architect 28-187, Lie Detector Kit 28-182, Light Operated Alarm Kit 28-128, Logix Electronic Computer SF-5000, Metal Locator Kit 28-181, Metronome Kit 28-118, Microcomputer Trainer 28-260, Moisture Detector Kit 28-132, Optical Lab Kit (SF-3000), Organ Kit 28-101, "OTL" Audio Amplifier Kit 28-106, Photo Electric Nite Lite Kit 28-126, Physics Experiments 28-193, Psycholite Kit 28-171, Sci Lab Kit 28-189, Short Wave Radio Kit 28-110 Solar Operated Radio Kit 28-129, Solar Power Electronic Lab Kit 28-246, Stereo Amplifier Kit 28-113, Stereo Preamp Kit 28-114, Super Snooper Kit 28-120, Telephone Amplifier Kit 28-116, VHF Receiver Kit K8-221, VOM Meter Kit 28-112, Wireless AM Mike Kit 28-103.