This site is devoted to vintage electronics -- radios and audio amplifiers. It is not about restoring and collecting vintage items, but rather about modifying them in attempt to improve performance and bring it closer to modern standards.
Collection of articles describe how by relatively small smart mod performance can be greatly improved. The mods can be applied to various stages: audio gain stages, output stages, local oscillators, mixers, detectors, power supplies. Original circuit ideas are discussed along the way.
Within this site, semiconductor solutions are used for the mods. It is a common knowledge that transistors and ICs outperform tubes almost everywhere, but completely overhauling a vintage set and converting it to a solid state design would be going too far. Much better is to keep a tube based skeleton, but insert semiconductor solutions here and there -- where the marked improvement can be achieved with minimum changes.
Only relatively simple solutions are covered here. For instance, to improve frequency stability of a short wave radio, we will not consider fitting a frequency synthesizer, but rather discuss using a JFET oscillator and a CMOS switch IC instead of say an old tired 6SA7 pentagrid converter tube.
Circuit ideas presented on the site might not be absolutely unique ("There is nothing new under the sun") but at least they are not very common. Preference is given to the elegant and simple solutions.