Pye_350C维修电路原理图.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 kvariable 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. RadioFans.CN 收音机爱 好者资料库 Page 2 4. Voltages and currents Table 2 gives the voltages and currents found on the same receiver when tuned to the HF end of the short waveband, but with no powerful signal present. The mains input was 240V. All voltages were measured with respect to chassis (except the AC voltage on the secondary of T2) using a 20,000 /V meter. The currents are approximate. 5. Operational notes The operation calls for no special comment. It works well with a contemporary moving iron loudspeaker. Overloading of the detector occurs on strong signals if the wrong aerial tapping is used. The volume control VR1 work as well as might be expected (ie not very!). Most of the effect occurs in the first few degrees of rotation. Reduction of volume by detuning the aerial circuit is frequently a better way than trying to use VR1. 6. Service notes On the particular receiver under test, all the fixed capacitors were tested for leakage and found, rather surprisingly, to be in good condition. The metal rectifier was also found to be in good condition, though the forward resistance is a trifle high. The secondary winding of T1 was open circuit, as was the wire-wound resistor R1. Both were re-wound. Notice that the spindle of VR1 is at HT potential. It is insulated from the metal front panel by means of an ebonite bush, which must be carefully replaced if removed. Care should also be taken if the moulded knob is removed! The moving vanes of the reaction capacitor are also at HT potential, but in this case they are insulated from the spindle. The moving vanes of VC1 and VC2 are not earthed. Do not attempt to dismantle the slow motion drives or remove the knobs - they are very difficult to re-assemble without damage. RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 Page 4 Table 1 - component values and functions Capacitors C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 1.0 F 1.0 F 1.0 F 1.0 F 1.0 F 0.0003 F 2.0 F 0.002 F 1.0 F 1.0 F 1.0 F 2 x 1.0 F 2 x 1.0 F 0.001 F V1 screen decoupling V1 bias decoupling V1 anode decoupling V2 anode decoupling V2 bias decoupling V2 anode HF bypass Loudspeaker coupling V3 anode HF bypass V2 bias decoupling (gram) Smoothing Smoothing Reservoir Rerservoir Mains RF filter common can common can Resistors R1a R1b R1c R1d R1e R1f R1g R1h R2 R3 3 k 2.7 k 29 k 18 k 48 28 70 680 100 k 100 k R1 a-h is the HT and bias potential divider. Total resistance = 53.5 k V2 bias decoupling V2 bias decoupling (gram) Others VR1 T1 L1 - L6 L7 L8 S1 S2 70 k Pri 1000 approx Sec 12 kapprox 400 approx 700 approx Volume control V2 - V3 coupling Tuning coils V3 output choke HT smoothing choke RF band switching Detector band switching DC resistance DC resistance DC resistance DC resistance S1 and S2 are mechanically coupled RadioFans.CN 收音机爱 好者资料库 Page 5 Table 2 - voltages and currents R Thornton 2004 Valve V1 (AC/SG) V2 (AC/HL) V3 (AC/P) Anode voltage (tap on R1 to chassis) (V) Anode curent (mA) Screen voltage (V) Screen current (mA) Bias voltage (tap on R1 to chassis) (V) 120 1.9 35.5 0.9 - 0.76 133 2.5 - - 2.4 (- 1.2 on gram) 155 7.8 - - 12.5 Voltage between C11 and C12 junction and chassis (V) : 166 Voltage across secondary of T2 (V rms) : 130 (AC) Total HT current (mA) : 15.1 RadioFans.CN 收音机爱 好者资料库