Restoration :
Repaif of a Philips 2517 by J. Cudraz.
During training courses of radio repair organized by the Radio­fil­istes de l’Isère association, a participant brought a receiver Philips 2517 to be repaired. It is a small sized set of 270 x 160 x 150 mm with a brown dark red Philite cabinet. It is a regenerative 3-valve receiver dated 1931 with three wave ranges from 200 to 2000 meters and with external high Z loudspeaker.

Technical pages :
Les ondes radio naturelles by C. Beghin.
Les ondes de plasma
This third part involves the natural waves generated through plasma instabilities triggered by high energy particles from solar origin. The Earth’s magnetic field, thanks to the shield called magnetosphere, prevents us against hard radiations and responds to solar flares by emitting radio waves. Routine ground observations in high latitude regions where the aurora borealis and australis take place, and furthermore scientific satellites, have permitted to understand the involved physical processes and to achieve a regular survey. The frequency domain extensively overlaps that of ELF-VLF described in previous parts, from tiny fraction of Hertz of the Ultra Low Frequencies (ULF), up to MHz in the High Frequency (HF) range, with signal durations from a few seconds up to several hours.

Realization :
Gooseneck loud-speakers by J-R. Malderez.
The horn speaker is the symbol of the early radio and also the logo of Radiofil. In French, it is called “neck of swan”. This analogy with the bird is twice justified: it has the graceful shape of the swan neck and is also able to produce sounds because, in the Greek mythology, the swan was the bird dedicated to Apollo, god of the song and music. All those reasons are widely sufficient to pay tribute in this object, the manufacturing of which was stopped before 1930 for the benefit of the diffusers, the ancestors of our current loud­speakers. My small collection includes about twenty copies with a poor quality sound. Only one of these objects distances sharply the others, it is the Duotone Brunet with its wooden horn shaped as flower petals that produces a sound of an exceptional quality.
Sauty bridge capacitance meter by S. Lecomte.
During repairing or restoring old electronic gears, it happens frequently enough to find components whose value is erased. It’s often the case of paper capacitors. The capacitor meter then becomes indispensable. Nowa­days the digital multimeters often offers this function. I don’t have this kind of meter in my lab, but only analogic meters, so I made a Sauty bridge capacitor meter which is an adaptation of the Wheatstone bridge.

Introductory courses :
L'Électronicofil : penthode solide by G. Prieur.
L’amplificateur BF idéal à semi-conducteurs
In this second part I suggest you to perform printed circuit boards implementing the concept of “ solid state pentodes ” developed in the previous article, which can replace (with better performan­ce?) pentodes of the preamplifier and final stages.
radiomail Premiers pas by J-P. Waymel.
radiomail est un nouveau service d’aide à distance pour la réparation de vos postes de radio. Il est important de rappeler ici ce qu’écrivait l’auteur à l’occasion du lancement de ce nouveau dispositif : « Il s’agit d’un service complémentaire à la revue, aux ouvrages publiés, aux stages d’initiation, au forum, en aucun cas un service concurrent ». Complémentaire aussi à l’aide apportée par tous les bénévoles qui répondent directement aux sollicitations et questions de ceux qui s’interrogent sur la restauration de leurs postes, notamment au travers des correspondants schémathèque. Dans cet article sont succinctement décrites les deux premières aventures radiomail ayant entraîné l’échange de 128 méls pour l’une et 63 pour l’autre ! Pour connaître les modalités de fonctionnement de radiomail, veuillez vous reporter à la page 7 du radiofil magazine no 47 et à la page d’accueil du site www.radiofil.com.

History of techniques :
La TSF by J-C. Montagné.
4e partie
Before further going through the evolution story of the radio, we ask our readers to make a stage in the last decade of the 19th century. Who were the first users of electromagnetic waves and what they were going to do with them? Today we ask no question anymore, because it is acquired. Let us go back to the end of the 19th century and set up the main actors of this conquest. We shall make a distinction between those who thought about " distant communication " and those who first designed to use this new phenomenon for other purposes.

Atelier :
Dépannage d'un poste Firestone by J-P. Tonnelier.
A few years ago, I outbade this attractive painted Bakelite small radio model "Firestone": 4-A-141 (1952), at the Chartres’ auction hall. Recently, I finally decided to make it live again and I admit to have been very surprised by this receiver model that I haven’t seen before.