The FISK RADIOLETTE MODELS 39 and 42B
Four Valve, Medium Wave, Battery Operated
Superheterodyne
TECHNICAL INFORMATION AND SERVICE DATA
THE FISK RADIOLETTE, MODELS 39 and 42B
Four Valve, Medium Wave, Battery Operated, Superheterodyne
TECHNICAL INFORMATION
Electrical Specifications
| TUNING RANGE | ALIGNMENT FREQUENCIES |
|---|---|
|
"Standard Medium Wave"200-550 meters
Intermediate Frequency |
R.F. Alignment |
|
CURRENT CONSUMPTION
"A" Battery at 2 volts "A" Battery at 2 volts |
|
|
VALVE COMPLEMENT
(1) 1C6Detector-Oscillator (2) 1C4I.F. Amplifier |
|
| Dial Lamp | |
|
Loudspeaker (Permanent Magnet) Types A.G.1 (39)
A.L.2 (42B). |
, Loudspeaker Transformer T.G. 51 (39),
T.G.131 (42B). |
General Circuit Description
The Radiolette is a four valve superheterodyne designed for battery operation. The plate supply is from "B" batteries and the filament supply from a 2 volt storage battery. The circuit description per stage is as follows:—
DETECTOR-OSCILLATOR.
The signal entering the aerial circuit is coupled to the control grid of the 1C6 through a tuned aerial coil T1. The local oscillator signal 460 K.C. higher in frequency is generated by the oscillator section of the 1C6. Within the 1C6 the signals combine to form the I.F. or beat frequency. No padding adjustment is required for the oscillator circuit since the padding condenser C6 is of the correct capacity and is matched to the oscillator coil at the factory. The oscillator and aerial coils are tuned by a two section variable condenser; each section is fitted with a compression type trimmer condenser for alignment purposes.
I.F. AMPLIFIER.
Two stages of I.F. amplification are used, in which three transformers are employed. Excepting the secondary of the third transformer, which is untuned, the primaries and secondaries are tuned
by compression type trimmer condensers. Amplification in the second I.F. stage is accomplished by the pentode section of the 1K6. The amplified signal is then coupled to the negative diode of the same valve by the third I.F. transformer for rectification across resistors R9 and R10. A signal is also fed to the positive diode by condenser C21, and, proportionate to the incoming signal, a D.C. potential is produced across R7 to be fed to the control grids of the 1C6 and 1C4 valves for automatic volume control.
AUDIO AMPLIFIER.
The Volume Control R9 selects the amount of audio signal to be transferred from the diode circuit to the control grid circuit of the 1K6, via C22, for audio amplification. Resistance capacity coupling is used to couple the plate circuit of the 1K6 to the control grid circuit of the 1D4 Output Pentode. The output of the 1D4 is transformer coupled to the permanent magnet dynamic loudspeaker.
Negative bias voltages are supplied by a 4½ volt bias "C" battery which is mounted in a clip on the chassis.
A switch located on the rear of the chassis is used to control the sensitivity of the Radiolette.
When the switch is in the local (L) position, R4 is connected in series with the screen feed resistor R3 to lower the screen grid voltage on the 1C6 and 1C4 valves. When the switch is in the Distant (D) position, R4 is omitted to raise the screen grid volt-
Alignment Procedure
Unless it is felt certain that the alignment of the Radiolette is incorrect, it is not desirable to alter the adjustments from the factory setting. However, when repairs have been made to R.F. or I.F. circuits or tampering with these circuits is suspected, complete alignment becomes necessary.
In aligning the tuned circuits it is important to apply a definite procedure, as described below, and to use adequate and reliable test equipment. An A.W.A. Modulated Oscillator Type C1070 is ideal for the purpose. Visual indication of the output from the Radiolette during alignment is also necessary, any output meter of conventional design being suitable
I.F. ALIGNMENT
The I.F. adjustments 1, 2, 3, 4 and 5 are shown in Figs. 2 and 3. Each circuit must be aligned to a basic frequency of 460 kilocycles.
To align, proceed as follows:----
- 1. Remove the grid clip from the control grid of the 1C6 and connect the output of the Modulated Oscillator, the ground connection of the oscillator being connected to the Radiolette chassis. See that a 250,000 ohms resistor is connected between the output terminals of the modulated oscillator.
- 2. Connect an output meter in the plate circuit of the 1D4 output pentode.
- 3. Set the Station Selector pointer of the Radiolette to 550 meters on the dial scale, and turn the Volume Control to the maximum clockwise position. Set the Local-Distant switch at the rear of the Radiolette chassis to the Distant (D) position.
- 4. Set the Modulated Oscillator to 460 K C and switch it ON
- 5. Adjust the output of the modulated oscillator so that a slight indication is apparent on the output meter.
-
NOTE.—The output of the modulated oscillator should be maintained at the lowest level consistent with a good output indication.
- 6. Beginning with adjustment No. 1 (see fig. 3) a non-metallic screwdriver is used to adjust the trimmer screw to a point where the maximum output reading is obtained. When the
age and thus increase the sensitivity.
The tone control circuit comprises a variable control connected in series with a .035 mfd. paper dielectric condenser between the plate of the 1D4 and earth
output meter becomes excessive, it should be reduced by adjusting the output of the modulated oscillator.
The Volume Control must not be used for this purpose, as inaccurate alignment will result if it is altered from the maximum clockwise position.
Proceed with adjustments 2, 3, 4 and 5 in the same manner. It is advisable to repeat the adjustments in the same sequence to assure that the maximum output is obtained.
R.F. ALIGNMENT
The R.F. adjustments are located on the variable condenser—see fig. 3. They are numbered in the correct alignment order continuing from the I.F. procedure, that is, 6 and 7.
To align, proceed as follows:------------------------------------
- 1. Connect the output of the modulated oscillator to the aerial terminal marked "A," the ground connection of the oscillator being connected to the Radiolette chassis
- 2. Set the Station Selector pointer at approximately 214 meters. See that the Sensitivity Switch is still in the distant (D) position.
- 3. Set the modulated oscillator to 214 meters (1400 K.C.).
- 4. Tune the Radiolette to the modulated signal and adjust the output of the modulated oscillator so that a slight indication is produced on the output meter.
-
NOTE.—The output of the modulated oscillator should be maintained at the lowest level consistent with a good output indication. The output of the modulated oscillator should be maintained at the lowest level consistent with a good output indication.
- 5 Reset the Station Selector pointer to 214 meters and adjust the oscillator trimmer (No. 6) with a non-metallic screwdriver to a point where the maximum reading is obtained on the output meter.
- 6. Adjust the aerial trimmer (No. 7) to give maximum output.
- 7. Tune the Station Selector carefully to the highest reading on the output meter and re-adjust the aerial trimmer.
| Code |
Part
No. |
COILS | Code |
Part
No. |
CONDENSERS | Code |
Part
No. |
CONDENSERS |
|---|---|---|---|---|---|---|---|---|
|
TI
T2 T3 T4 T5 T6 |
1560
2893 1523A 1523B 1530A |
Aerial Coil
Osc. Coil First I.F. Transformer Second I.F. Transformer Third I.F. Transformer TG53 (R39), TG131 (R42B) |
CI
C2 C3 C4 C5 C6 C7 C7 |
2891 |
.05 mfd. Paper
10-50 mmfd. Mica Trimmer Variable Condenser 50 mmfd. Mica (D) 15 mmfd. Mica (C) 410 mmfd. Mica Padding 10-50 mmfd. Mica Trimmer Variable Condenser |
C29
C30 C31 |
.035 mfd. Paper
.005 mfd. Paper .5 mfd. Paper |
|
| RESISTORS |
C9
C10 |
2071 |
.05 mfd. Paper
130 mmfd. Mica (H) |
|||||
|
RI
R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 |
1507
2762 |
60,0000 ohms, 1 watt
50,000 ohms, 1 watt 75,000 ohms, 1 watt 50,000 ohms, 1 watt 11 Megohms, 1 watt 12 Megohms, 1 watt 13 Megohms, 1 watt 14 Megohms, 1 watt 500,000 ohms, 1 watt 500,000 ohms, 1 watt 500,000 ohms, 1 watt 1 Megohm, 1 watt 1 Megohm, 1 watt 1 Megohm, 1 watt 1 Megohm, 1 one Control |
10-50 mmfd. Mica Trimmer
10-50 mmfd. Mica (H) 5 mfd. Paper .1 mfd. Paper 130 mmfd. Mica (H) 10-50 mmfd. Mica (H) 10-50 mmfd. Mica Trimmer 130 mmfd. Mica (H) 200 mmfd. Mica (J) 700 mmfd. Mica (J) 700 mmfd. Mica (J) 130 mmfd. Mica (J) 130 mmfd. Mica (H) 10-50 mmfd. Mica Trimmer 700 mmfd. Mica Trimmer 700 mmfd. Mica So mfd. Paper |
Fig. I.—Circuit Diagram and Code
Fig. 2.—Layout Diagram (underneath view).
8. Disconnect the modulated oscillator and connect an aerial and an earth wire to the Radiolette. Tune a broadcasting station of wave length between 450 and 550 meters. If there is an error in the calibration of the Radiolette, reset the pointer by loosening the mounting screws. Next, repeat instructions 5, 6 and 7 to complete the calibration.
These models employ a fixed padding condenser (C6) which is matched to the oscillator coil, thus eliminating a padding adjustment. Do not, at any time, separate the padding condenser from the coil to which it is fitted.
RESISTANCE MEASUREMENTS.
The resistance values shown in fig. 4 have been carefully prepared so as to facilitate a rapid check
of the circuit for irregularities. To obtain the full benefit from this diagram it is advisable to consult the circuit and lay-out diagrams while conducting the check. Each valve should hold within ± 20% Variations greater than this limit will usually be indicative of trouble in the basic circuits.
TUNING COILS (TI-T2).
Each coil is secured in its shield by a circular retaining spring which can be seen seated in a recess between the shield and the coil base. To remove the coil, disconnect the leads from the lugs and insert a small screwdriver between the spring and the shield, then ease the spring from the recess.
A coloured dot on the coil base denotes the grid connection, and fig. 2 shows the correct position for this dot when replacing a coil.
Fig. 3.—Layout Diagram (top view).
Fig. 4.—Resistance Diagram.
Resistance values were taken with the values removed from sockets, variable condensers in full-mesh, volume control in maximum clockwise position and sensitivity switch in local (L) position.
SOCKET VOLTAGES.
| VALVE |
Chassis
to Control Grid Volts |
Chassis
to Screen Grid Volts |
Chassis
to Plate Volts |
Plate
Current M.A. |
Filament
Volts |
|
|---|---|---|---|---|---|---|
| 1C6 | Detector | *1.5 | 45 | 120 | 1.0 | 2.0 |
| Oscillator | . — | _ | 55 | 1.5 | ||
| IC4 | I.F. Amplifier | *1.5 | 45 | 120 | 1.5 | 2.0 |
| IK6 |
Reflex Amplifier
and Detector |
*1 . 5 | *50 | *55 | 0.75 | 2.0 |
| ID4 | Output Pentode | *4.5 | 120 | 115 | 6.0 | 2.0 |
Measured with controls in maximum clockwise position and with sensitivity switch in distant (D) position. No signal input.
*Cannot be measured with ordinary voltmeter.
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