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CIRCUIT NOTES
Record Player Diagrams, Wireless and Complete
Record players of the wireless type have been very popular because of their ease of installation.
Generally, they are conventional converter tubes in oscillator circuits which use the plate of the tube. The voltage from the pick-up is usually connected to the grid nearest the cathode in order to get a good percentage of modulation.
The Fig. 1 shows the wireless oscillator used by Zenith in models S9001
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GENERAL m ELECTRIC
Fig 1 — Wireless phono oscillator circuit in Zenith model S9001. Crystal pick-up
is connected to number 1 grid in the loctal converter tube. Note that the phono
motor is in series with filaments.
and S9002. Note that the phonograph motor operates in series with the tube filaments.
Fig. 2 is the wireless player Silvertone model 7061. Here, the phono pick-up voltage is used to modulate the screen grid of the 35L6GT. The screen voltage is blocked, with the 0.05 capacitor, from the crystal pickup. The radiating antenna is capacity coupled to the plate of the oscillator and is a third wire in the power line cord.
The complete record player in Fig. 3 is a Silvertone model 5815. In this circuit, the pick-up voltage modulates the control grid of the 35L6GT. A shunt tone control is across the output transformer. The turntable motor is controlled by a separate switch.
TRACING HUM
In tracing down hum. on the wireless players, check to be sure that the lead from the pick-up to the modulator grid is well shielded and away from filament or rectifier circuits. Be sure
that the filter sections are doing their job. If the hum still remains, try a
Fig. 3 — A complete record player using beam power tube, control grid modulated.
lower value of resistance from the modulator grid to ground. In the case of the screen grid modulated types, better filtering is the answer.
Fig. 2 — This wireless player uses a beam power output tube and modulates the screen grid with the pick-up voltage. A third wire in the power line cord acts as
the antenna.
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