Guides from the bench
The original magazine recorded amplifiers one listing at a time. These guides fill in what the listings assumed you knew: what is inside the chassis, why one amplifier has four output tubes and another has two, what a tube tester really measures, what to check before you pay for an old amplifier, and what to do when a whole collection lands in your lap.
They are written by the people keeping this archive, checked against published sources, and linked to the model pages they mention, so you can go from a circuit idea to a real example and back.
7 min read
How a tube amplifier works, stage by stage
Input triode, phase splitter, output pair, transformer, feedback, power supply: the five places to look in any old amplifier.
6 min read
Push-pull or single-ended: what the output stage decides
One tube carrying the whole waveform, or two sharing it. Power, distortion, transformers and the speakers each design needs.
5 min read
Ultra-linear explained: Blumlein's tap and the Philadelphia badge
A screen-grid tap on the output transformer, a 1937 patent, a 1951 magazine article, and a word that became a sales badge.
6 min read
Buying and checking a vintage tube amplifier
Never switch on cold. Then: transformers first, chassis second, tubes last, and a realistic list of what a restoration costs.
6 min read
6L6, EL34, KT88, 12AX7: a field guide to amplifier tubes
Why a 6CA7 is an EL34, what the G and GT suffixes mean, and the dates and output figures for the tubes in this archive.
6 min read
How a tube tester works, and what its needle is not telling you
Drugstore emission checkers, Hickok mutual conductance testers and modern curve tracers, and how to read a seller's numbers.
6 min read
Allied Radio, Bogen, Dynaco and EICO: the people's hi-fi
Knight-Kits from Chicago, Challenger PA amps, the Stereo 70 and EICO test gear: the companies behind most American amps here.
10 min read
Inherited a vintage amp or hi-fi collection: what it's worth and how to sell it
Leave the switches off, photograph the serials, keep the pairs together, and get two kinds of offer before anything leaves the house.