Channel selector P 21808

The P 21808 is a transistorised television channel selector with continuous tuning, made by Electronica in Bucharest, with germanium PNP transistors; mechanical switching [1].

Transistorised channel selectors replaced the complicated and heavy turret tuners (rotactors); the book states that Romania was the first country in the world to put transistorised channel selectors with continuous tuning for the OIRT standard into production, in 1969 [1]. Electronica made three types: the P 21808 with germanium PNP transistors and mechanical switching, the P 22087 with silicon NPN transistors and mechanical switching, and the P 22211 with silicon NPN transistors, varicap tuning and electronic switching; they were later diversified for bands I, II and III to both the OIRT and CCIR standards [1]. The selector is a printed circuit with 3 transistors and 3 varicap diodes, fully shielded in a box of about 70 × 57 × 21 mm, switched by a pertinax strip carrying sliding contacts [1].

The memoirs of its designer say that Electronica’s germanium varicap selector, developed in 1967–1968, used mesa transistors AF109R and 2 × AF106 and three Siemens BB 109 varicap diodes [2]. With Telonic sweep generators imported from the USA, a varicap selector was aligned in 3 minutes, against 20–30 minutes for the Orega licence rotary tuner with 48 switched coils [2]. Electronica sold a licence for a 12-channel VHF selector to the FCC standard to the Wagner-Stein group in Santiago (Chile), with kits, Telonic test equipment and technical assistance; the Chilean factory exported selectors to Argentina and Brazil [2].

Main parameters: supply 12 V (+5%, −10%), varicap voltage 2–29 V, consumption under 20 mA, input 75 Ω unbalanced, gain over 19 dB on all channels, noise figure under 9 dB, IF rejection over 38 dB (band I), 40 dB (band II) and 46 dB (band III), image rejection over 46 dB (bands I, II) and 40 dB (band III), AGC range over 25 dB, ambient temperature +10 °C to +35 °C [1].