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regency: Pocket Radio; Regency TR-1: The Regency Radio Receiver

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » regency: Pocket Radio; Regency TR-1: The Regency Radio Receiver
           
Dietmar Rudolph
Dietmar Rudolph
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08.Aug.12 20:47
 
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The Regency Radio Receiver TR1 is described in "Kiver, M. S.: Transistors in Radio, Television, and Electronics, McGraw-Hill, 2nd. ed., 1959"

THE REGENCY RADIO RECEIVER

The first transistorized portable radio receiver to appear commercially was the Regency model TR 1, and it took advantage of every space saving feature afforded the transistors and associated miniature components (see Figs. 1 and 2). Over all dimensions of the unit are 5 by 3 by 1,25 in., enabling the entire set to fit easily into the pocket of a man's jacket. Weight of the set, with the batteries, is only 12 oz.

Fig.1. The Regency model TR-1 transistor radio is small enough to fit in the pocket of a man's jacket (Coutesy Regency.)

Fig.2. Inside view of Regency model TR-1 transistor receiver showing layout of components. (Courtesy Regency.)

The schematic diagram of this receiver is shown in Fig. 3. There are four transistors and five stages. The extra stage is the second detector, and its function is performed by a germanium diode, here either a Raytheon CK706A or a Tungsol TS117. The transistors are of the NPN variety, and three special designs are used for the converter, i f, and audio stages. Manufacturer of these units is Texas Instruments, Incorporated.

The first stage, containing transistor V1, is essentially a self oscillating converter. The input signal is picked up by a tuned ferrite core coil which possesses a high Q. A low impedance winding on the antenna coil couples the signal to the base of V1.

Local oscillations are generated by a parallel resonant circuit in the emitter circuit which is inductively coupled to a coil in the collector circuit. The low impedance emitter is tapped down on the tuned circuit in order to provide the proper impedance match without lowering the Q of the circuit.

The foregoing oscillator arrangement is a fairly common one. Its equivalent vacuum tube circuit is shown in Fig. 4. With the incoming signal and the local oscillator voltage both being applied to the converter transistor, the appropriate i f signal is formed and then fed to transformer T1 and the i f stages beyond.

A 10,000 ohm resistor is placed in the emitter circuit to provide d c stabilization against temperature changes and variations among different replacement transistors. The positive voltage which the emitter current develops across R2 is counterbalanced by a positive voltage fed to the base from the battery. The actual voltage difference between these two elements is on the order of approximately only 0.1 volt.

The proper biasing voltage for the collector of V1 is obtained from a 2,200 ohm resistor which is tied to the 22,5 volt B+ line. A 0.001 μf bypass capacitor C7 keeps the signal currents out of the d c distribution system.

There are two stages in the i f system, and both operate at 262 kc. This frequency is considerably below the 465 kc common in vacuum tube radio receivers, and it possesses the disadvantage of making this receiver more susceptible to image frequency pickup. However, the lowered frequency of operation is advantageous in that it provides greater gain and more stability.

The primary of each i f transformer is tuned with a fixed capacitor, while the secondary is untuned. This is done to match the high collector impedance of the preceding stage to the low input impedance of the following stage. Peaking of each i f coil is achieved by varying the position of an iron core slug.

Each i f stage is neutralized by feeding back a voltage from the base of the following stage to the base of the preceding stage. The feedback occurs through a 560 ohm resistor and a 100  to 200 μμf series capacitor. The capacitor value is not specifically indicated, because its exact figure will depend upon the internal capacitance of the transistor and this may vary from unit to unit. Actually, what happens in this particular receiver is that whenever a replacement i f transistor is ordered from the set manufacturer, a suitable neutralizing capacitor is sent along too, and both components must be replaced. Whether or not an i f stage will require neutralization depends upon the collector-to base capacitance of the transistor being used. In special high frequency transistors, this internal capacitance may be small enough so that the neutralization may not be needed, especially at the lower radio or intermediate frequencies as in a receiver to be described. However, where this capacitance is large enough to cause noticeable feedback, neutralization, as shown in Fig. 3, must be used.

Automatic gain control is applied to the first i f stage only. A negative voltage is obtained from the second detector and applied to the base of V2. Its purpose is to regulate the emitter and collector currents and, with this, the stage gain. When the incoming signal becomes stronger, the negative a g c voltage rises, reducing the collector current of V2 and, with it, the gain. The opposite condition prevails when the signal level decreases. This method is quite effective and provides a wide range of control.

The base bias for the second i f stage is obtained from the emitter of the audio output stage (which here operates class A). This bias voltage is heavily bypassed by C21, and then further bypassed by C13, a 0.05 μf capacitor.

Both emitters have d c stabilizing resistors. (If it were not for the presence of C8, C11, C13, and C15, signal degeneration would occur also. As it is, only the direct portion of the current passes through R5 and R8.) Note, however, that the emitter resistor of the first i f stage is only 560 ohms in value whereas the emitter resistor of the second stage is 2,700 ohms. The reason for this difference stems from the compromise that must be reached in the first i f stage between good a g c action and the d c stability of the amplifier. A value of R5 greater than 560 ohms is desirable for stability purposes, but the degeneration that produces the stability would result in reduced gain control action.

Each of the collectors of V2 and V3 receive their operating voltages through 2,200 ohm dropping resistors. C11 and C15, at the top end of the resistors, serve as decoupling and bypass capacitors.

Following the second i f stage is the second detector, and this function is performed by a germanium diode. The load resistor for the detector is the volume control. Note the impedance of the control, 1,000 ohms; this low value is needed to match the input impedance of the audio output stage V5.

The final amplifier is operated with the emitter grounded through a 1,000 ohm resistor. Base bias is obtained from the voltage divider network formed by R13 and R14. The output transformer matches the 10,000 ohm collector impedance of V5 to the low voice coil impedance of the miniature speaker. Diameter of the speaker is only 2,75 in. Provision also exists for a small earphone plug which can be inserted into a small jack on the side of the receiver. When the earphone is in use, the speaker is disconnected.

The total power for the receiver is furnished by a hearing aid type of 22,5 volt battery. Total current drain is on the order of 4 ma.

The compactness of this receiver can be seen by an inspection of Fig. 2. All components, including the two gang tuning capacitor and the speaker, are miniaturized. Operating voltage on electrolytic capacitors, C9, C21, and C19 is 3 volts; on C17, it is 25 volts.­

 

  
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