Duplex four SMC early

McMichael Radio Ltd.; Slough

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  • Année
  • 1933/1934
  • Catégorie
  • Radio - ou tuner d'après la guerre 1939-45
  • Radiomuseum.org ID
  • 178620
    • alternative name: McMichael, Leslie

Cliquez sur la vignette du schéma pour le demander en tant que document gratuit.

 Spécifications techniques

  • No. de tubes
  • 4
  • Principe général
  • Récepteur TRF - par réaction (régénératif); 2 Etage(s) BF
  • Circuits accordés
  • 2 Circuits MA (AM)
  • Gammes d'ondes
  • PO et GO
  • Tension / type courant
  • Piles (rechargeables ou/et sèches) / 2 & 126 Volt
  • Haut-parleur
  • HP dynamique à aimant permanent + bobine mobile / Ø 5 inch = 12.7 cm
  • Puissance de sortie
  • 0.3 W (qualité inconnue)
  • Matière
  • Cuir / canvas / plastique mais autre matériel en dessous!
  • De Radiomuseum.org
  • Modèle: Duplex four SMC [early] - McMichael Radio Ltd.; Slough
  • Forme
  • Portative > 20 cm (sans nécessité secteur)
  • Dimensions (LHP)
  • 390 x 220 x 380 mm / 15.4 x 8.7 x 15 inch
  • Remarques
  • The early model SMC has a manual volume control by means of a variable filament current for the RF stage, while the late model used to vary the RF stage grid bias.
    This is a leathercovered suitcase model. The lid of the case contains the frame aerial and the loudspeaker.
  • Poids net
  • 13 kg / 28 lb 10.1 oz (28.634 lb)
  • Schémathèque (1)
  • Hardware analysis.

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Contributions du forum pour ce modèle: McMichael Radio Ltd.: Duplex four SMC

Discussions: 1 | Publications: 1

There is an early version applying manual gain control by means of filament variation in the RF stage.

This was state of the art for battery triodes in the late 1920's.

But now the RF triode was replaced by a superior screen grid valve. Such a valve is behaving different to filament variations, in particular at low emission for low gain, where the setting is rather unstable.

Obviously led this drawback to a redesign of the volume control by leaving the filament on full supply while a variable grid bias was introduced. This results in an easier and smoother control function.

The available documentation describes the late version only.

The early version was on my workbench for repair. It had a low resistance rheostat (original, physically identical with the high resistance potentiometer in the late version) but some "repair" attempts of previous owners left a chaos: senseless resoldered wires, wrongly connected on-off-switch etc.
He must have desperately decided to sell the spoiled thing after replacing two original Audios by defect ones (different brands; all 4 windings open), putting four valves with open filament. The next owner (in Germany) could not do much better and sold it again. 
Now the buyer asked me for help.
I can proudly report that the radio is back to life now (after spending about 3 days to navigate through the wiring jungle and the wrong map (schematic)...

 

Konrad Birkner † 12.08.2014, 20.Jul.10

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