~ Early Web Links ~

SchematicsForFree is a volunteer-run archive offering free electronics schematics, circuit diagrams, and service manuals covering audio, video, automotive, and test equipment. Updated regularly since 2022, it embodies the original open-sharing spirit of the web, providing hard-to-find technical documents at no cost.

Circuit Sage offers free design routines and tools for analog and RF circuit engineers, covering topics like PLL design, LNA/PA design, impedance matching, bandgap references, and transmission lines. The site provides Mathcad-based calculation routines that serve as practical references for IC and wireless circuit design work.

AimSpice appears to be a SPICE circuit simulation software site, offering tools for electronic circuit analysis and modeling. The minimalist page redirects visitors to the main document, suggesting a focused software or technical resource for electronics engineers and hobbyists.

HobbyProjects.com curates an extensive collection of links to electronics tutorials, circuits, engineering projects, and useful resources for hobbyists at all skill levels. The site also offers its own tutorials covering topics from basic electronics to microcontrollers, along with dictionaries, formulas, and reference materials for electronics enthusiasts.

RED Free Circuit Designs is a hobbyist electronics resource offering dozens of free audio amplifier schematics, preamplifier modules, headphone amplifiers, and miscellaneous electronic circuit designs. Visitors can browse Class-A and Class-B amplifier projects, phono preamps, intercom circuits, and many more practical designs, all available at no cost.

A specialized reference guide cataloging the vacuum tube types used in shortwave radio broadcast transmitters, organized alphabetically and numerically for easy lookup. The site also lists manufacturers, rebuilders, and distributors worldwide, including companies like Thales, Eimac, Penta Laboratories, and Xuguang, making it a practical industry directory for broadcast engineers.

CircuitsArchive is a free, web-based archive of electronic circuit schematics covering everything from audio gear and battery monitors to filters, telephone interfaces, and microprocessor circuits. Maintained by Nicola Asuni since 1998, it offers a well-organized collection of PCB designs and projects useful to hobbyists and engineers alike.

A comprehensive free electronics and electrical engineering reference hub covering everything from basic electricity and Ohm's Law to advanced RF design, DSP, amateur radio, and circuit simulation. With hundreds of curated links, formulas, tutorials, data sheets, and calculators organized across multiple phases of learning, it serves as a structured self-study guide for electronics enthusiasts and engineers alike.

KA7OEI is Clint's technically-focused amateur radio and electronics blog, covering hands-on modifications and experiments with devices like the MFJ-5008 parabolic ultrasonic receiver. This particular post dives deep into improving the sensitivity and frequency response of the discontinued ultrasonic tool, with detailed photos, circuit analysis, and practical applications like bat detection and power line fault finding.

Andrews Communications is an Australian retailer specializing in marine radio, telescopes, binoculars, scanners, CB radio, and test equipment. The shop serves customers across Australia with a broad range of optical and electronic communication products.