RADIO SERVICING

BUSH Models TR 130 and TRI30D

General Description: Models TR130 and TR130D are battery­operated portable receivers, each using seven transistors and one crystal diode, and covering the Long and Medium wavebands. An additional range provides electrical bandspread of the high frequency end of the Medium waveband. Both models are electrically identical, differing only in presentation.

Wavebands: L.W. band: 1070-1900 m. (280 to IS8 kc/s.). M.W. band: 187-S70 m. (160S to S2S kc/s.). B.S. band: 187-210 m. (160S to 1430 kc/s.).

Battery: One 9-volt Ever Ready type PP9 or Drydex type DT9. The battery consumption is IS mA. quiescent and 2S mA. at average listening level.

Transistors (Mullard Type): VTl (AFII7) Mixer/oscillator. VT2 (AFII7) I.F. amplifier. VT3 (AFII7) I.F. amplifier. VT 4 (OC71) Audio amplifier. VTS (OC81D) Driver stage. VT6 (OC81), VT7 (OC81) Push-pull output.

Crystal Diode: CDl (OA90) Detector. Earpiece Socket: A socket is provided at the side of the receiver into

which may be plugged an earpiece of 20-1000-ohms impedance. Alterna­tively, this socket may be used with an external loudspeaker of Is-ohms impedance.

Tape Recording: No special provision has been made, but the earpiece socket provides a low-impedance output source to which a tape recorder may be conducted. The connecting lead should be terminated with a resistor of about I S ohms. It should be noted that the internal loudspeaker will be muted when using this method of recording.

CAPACITOR F42 DRIVE DRUM

DRIVE CORn 106

BUSH

Dismantling: Place the cabinet face downwards, remove the detachable base, then remove the battery. Separate the two halves of the cabinet by releasing the two fasteners contained within the mouldings, then lift the back section clear. (Note: Dismantling to this stage will permit the R.F. align­ment procedure to be carried out.) Unscrew the two 4BA nuts retaining the chassis to the speaker pillars, then loosen the two self-tapping screws securing the top edge of the chassis to the die-cast lugs of the top assembly. Lift out the chassis, unsoldering the loudspeaker leads if required. Replace the chassis by reversing the above procedure.

Replacement of Drive Cord: Note: About 36 in. of Terylene cord will be required for the new assembly. Remove the chassis from the cabinet as described in the dismantling procedure above. Carefully ease the scale pointer from its carrier then remove the four Phillips head screws securing the scale plate to the chassis. Lift the plate clear. Withdraw the circlip located on the end of the tuning spindle, then loosen the grubscrews securing the capstan to the spindle and withdraw the tuning spindle complete with knob. Lift the capstan clear, noting the position of the nylon bearing to ensure its correct replacement. Set the tuning capacitor so that the vanes are approximately half meshed. Now from a point half-way along the new length of cord, make a loop of one turn round the spigot contained within the drive drum, passing the cord ends out through the slots in the drum. Assemble the cord drive and then refit the capstan. Finally pass the ends of the cord through the eyelet, knotting them under tension from the spring-loaded pulley mounted above the Off/On volume control.

Note: When refitting the scale pointer, ensure that it registers with the datum marks on the right of the scale when the tuning capacitor is fully meshed.

Adjustment of RV3: The replacement of components in the output stage may necessitate the resetting of RV3. This may be done by setting an AVO model 8 to the 50 /LA. D.C. range, and connecting it across R30, observe correct polarity. With the volume control set to minimum, adjust RV3 in accordance with the table below:

Ambient temp.

°C OF

18 65 23 73 28 82 33 91

Meter reading (50 /-,A. f.s.d.

9'24 1l'08 12·8 15'04

Equivalent I. in mA. of

mV. (across R30) output pair

23'1 7'0 27'72 8'4 32'01 9'7 37.62 11'4

Alignment Procedure: Equipment required: An A.M. signal generator to cover 158-1605 kc/so An output wattmeter with a range 0-1 watt to match 15 ohms impedance. A non-metallic trimming tool for adjusting the iron cores and R.F. trimmers. A 10-pF. capacitor for injecting R.F.

107

RADIO SERVICING

signals into the aerial socket; a o·l-fLF. capacitor for I.F. lllJection, and an 8'2 kO-resistor for temporarily desensitising the receiver under conditions of interference. If the cabinet back is removed, R.F. alignment may be carried out without taking the chassis out. The chassis must be withdrawn, however, for I.F. alignment. The signal generator should be switched on about 15 min. before commencing the alignment. Connect the output meter to the receiver by means of the earpiece socket if a suitable plug is available. Set the receiver volume control to maximum, and the tone control to maximum treble response. During the alignment the signal input should be adjusted to maintain the output at 50 mW. (20 mW. if the loudspeaker is left in circuit) each time a trimming adjustment is made.

I.F. Alignment: Note: The outer peak is the correct one for all I.F.T. adjustments. Switch the receiver to the Medium waveband and set the tuning pointer to about 300 m. Set the signal generator to 470 kc/s., modu­lated 30 per cent. at 400 c/s. Connect the output via a o· I -mfLF. isolating capacitor to the junction of RI and CS, the chassis being the return point for the signal. Align I.F.T.3, I.F.T.2 and I.F.T.I, in that order, for maximum audio output. Align each transformer once only.

R.F. Alignment: Notes: Ensure that the tuning pointer is in line with the datum marks on the right of the tuning scale with the tuning gang fully meshed. The signal generator should be connected to the aerial socket via a 10 pF. capacitor. Under conditions of interference, the receiver may be temporarily desensitised by connecting an 8'2kO resistor between the junction of R7 and RII and the chassis.

Operation

1 2

3 4 5

1 2

3

Waveband

M.W. M.W.

Sig. gen. frequency (mod. 30% 400 c/s.)

Oscillator Circuits

600 kc/so 1500 kc/so

I

Tuning pointer setting

500 m. 200 m.

Repeat operations I and 2 and check calibration

L.W. 214 kc/so

I 1400 m.

I B.S. 1439 kc/so Luxembourg· B.S. 1500 kc/so Carolinet

M.W. M.W.

Aerial Circuits

600 kc/so 1500 kc/so

500 m. 200 m.

Repeat operations I and 2 for optimum gain at both points

Adj�stfor maxtmum

output

CI6 L8/9/IO C40

L2/3 Cl

L.W. 214 kc/so

I 1400 m. C6

B.S. 1500 kc/so Carolinet C3

• Set the pointer to be coincident with the letter" m " of this station name. t Set the pointer to be coincident with the letter" 0 " of this station name.

108

BUSH

FRONT CHASSIS

F44 PRINTED WIRING BOARD

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eASES Of TRANSISTORS

osc. COl l VIEWED FROM TOP

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DRIVER TRlM SfORHER (T.I ) VIEWED fROM TOP

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OUTPUT TRANSFORMER (T.2) VIEWED FROM Tor

CIRCUIT DIAGRAM-BUSH MODELS TRI30 AND TRI30D

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I VOLTAGES SHOWN ARE NEGATIVE WITH RESPECT TO CHASSIS AND MEASUREO WITH AVO N.8 UNDER NO' SIGNAL CONDITIONS AND WITH VOLUME (ONTROL SET TO ZERO

Z ALL VALUES Of RESISTANCE IN .HMS AND ALL VlL�S OF CAPACITANCE IN ,..F UNLESS OTHERWISE STATED.