PYE (GB) Pye 350C free download

File name Pye_350C.pdf

Pye 350/C All-Electric 3 1. General The Pye All Electric 3 model 350/C is a three valve, two waveband AC mains TRF receiver. A separate high impedance loudspeaker is required for the set, which embodies a screen grid HF stage (V1, AC/SG), a triode anode bend detector (V2, AC/HL) and a triode output stage (AC/P). A Westinghouse metal rectifier of early design (no cooling fins) is incorporated in the HT power supply, which operates on a voltage doubler principle. The HF and detector stages are tuned separately. The wavelength coverage is approximately 900 - 2300 metres ("long waves") and 210 - 520 metres ("short waves"). 2. Circuit details The circuit diagram is below. The aerial circuit is tuned by L1 or L2 and VC1, which has an edgewise slow motion drive and drum scale. Two separate aerial input tappings are provided. V1 is a conventional indirectly heated screen grid valve. This is coupled via L3 or L4 to the detector tuned circuit, L5 or L6 and VC2. The waveband is selected by the mechanically ganged switches S1 and S2. The detector is a triode wired as an anode bend detector. This circuit is unconventional in that reaction is provided via the solid dielectric differential capacitor VC3 giving feedback to L5 or L6. The reaction winding is itself a part L5 or L6, and so is incorporated in the tuned circuit. Neither the aerial nor detector tuned circuits have a DC connection to chassis, as they are incorporated in the valve biasing arrangements. The detector is coupled to the output stage V3 with an intervalve LF transformer (T1). A 70 k variable resistor (VR1) connected across the T1 primary acts as a crude volume control. The output valve is choke-capacity coupled to a loudspeaker using L7 and C7. The power supply for the valve heaters is derived from a 4 volt centre tapped winding on the mains transformer T2. The HT winding is connected to a rectifying and voltage doubling circuit (C12, C13, MR1). Smoothing is accomplished by the choke L8 and capacitors C11 and C10. The HT appears across the resistor R1, which is a sectionally wire wound component. The HT and bias supplies for the valves are picked off from tappings on V3. Mains voltage adjustment is provided by tappings on T2 primary. Provision is made for using the set with an electric gramophone pick-up. The intermediate position of S1/S2, between long and short waves, breaks all contacts except S2g, and the detector valve bias conditions are altered so that it acts as a conventional amplifier. Notice that the decoupling components C3, C4, C5 all share a single can, as do the smoothing capacitors C10 -C13. C12 and C13 consist of pairs of capacitors wired in parallel. 3. Component values The component values are given in Table 1. The capacitors were measured from an actual receiver (serial number C26118) using a Wheatstone bridge followed by "rounding" to the probable design value. Resistances were measured on a multimeter.