Eddystone Transistorised Communication Receiver Model EC10 Instruction Manual

Introduction

The Eddystone Model EC10 is a fully transistorised single conversion communication receiver covering the frequency band 550 kc/s to 30 Mc/s in five ranges. It provides for AM and CW reception and is powered by a self-contained battery pack. The unit employs ten transistors and five diodes, including a zener type for supply stabilisation, ensuring consistent performance with falling battery voltage. Current drain is kept to a minimum for extended battery life. A wide variety of aerials can be accommodated, including a small telescopic rod aerial for portable operation. An internal five-inch loudspeaker is fitted, with provision for low impedance telephones. A push-pull audio output stage is used, with a selective audio filter for CW reception under severe adjacent channel interference. Independent RF and AF Gain controls are fitted, along with separate BFO and AGC switches and a variable BFO pitch control. The tuning drive is geared and flywheel-loaded for ease of operation, featuring nine-inch scales calibrated directly in frequency. Dial illumination is provided and controlled by a panel switch. The receiver is lightweight, contemporary in styling, compact, and housed in a strong metal cabinet, ensuring reliable operation worldwide.

Image Description: The Eddystone EC10 receiver is depicted as a vintage tabletop communication radio. It features a dark-colored metal cabinet with a prominent front panel. The front panel includes a large frequency tuning dial with clear markings, a speaker grille, and several control knobs for functions such as RF Gain, AF Gain, BFO, TUNING, WAVECHANGE, and PHONES. Indicator lights and a tuning meter are also visible.

Technical Data

Frequency Coverage: 550 kc/s to 30 Mc/s in 5 ranges.

Intermediate Frequency: 465 kc/s.

Semiconductor Complement:

Power Supply: 9V from 6 x 1.5V leak-proof dry cells; external supplies of 12V or 24V DC (positive earth) using Voltage Converter Type 945 or standard AC mains supplies using AC Power Unit Type 924.

Consumption: 36mA quiescent, 77mA at 50mW and 180mA at 500mW output. Dial lamps add 90mA to the normal current drain.

Aerial Input Impedance:

A high impedance input connection is provided for use on all ranges and is suitable for use with short rod aerials.

Sensitivity:

IF Selectivity: Typical overall bandwidths at 6dB and 40dB down are 5 kc/s and 25 kc/s respectively.

IF Breakthrough:

Image Rejection: 20dB at 18.0 Mc/s and 50dB at 2.0 Mc/s.

Calibration Accuracy: 1% on all ranges.

Frequency Stability: Drift does not exceed 1 part in 10° per °C change in ambient temperature.

AGC Characteristic: An 80dB increase in signal produces less than 12dB change in output. Taken from 6uV at 2.0 Mc/s on Range 4.

Audio Output and Response: The maximum audio output exceeds 1 watt and 800mW is available at 10% distortion. Frequency response is level within 6dB over the range 300 c/s to 8 kc/s, except when using the audio filter. The filter is resonant at approximately 1,000 c/s and can be brought into circuit for selective CW reception. 6dB bandwidth is of the order 180 c/s.

Dimensions and Weight:

Circuit Description

The RF Section comprises TR1, TR2, and TR3 (3 x OC171). TR1 acts as a grounded-base amplifier with signal input applied to its emitter from a tap on the selected tuned circuit. An IF rejector circuit is included for Range 5 to limit IF breakthrough. Manual gain control is effected by RV1, which also controls the 1st IF Amplifier (TR4). The RF Stage is coupled to the Mixer (TR2) via low impedance secondaries. Oscillator injection is to the emitter, and IF output is taken to the 1st IF transformer (IFT1).

The Local Oscillator Stage (TR3) employs a tuned collector circuit that tracks above the signal frequency on all ranges. Injection for the Mixer is from a low impedance link winding on the oscillator coil. All three RF stages are powered from the stabilised supply provided by zener diode D3 (OAZ203), maintaining a nominal 6.5V for constant performance.

IF amplification is provided by TR4 and TR5 (2 x OC171) operating at 465 kc/s, with five tuned circuits for high adjacent channel selectivity. AGC and manual gain control are applied to the first stage, while the second operates at constant gain. A diode switch (D1: OA70) introduces a damping resistor (R19) across IFT1's primary under strong signal conditions to assist the AGC circuit and prevent overloading. The detector (D2: OA90) also provides the AGC voltage, applied to TR1 and TR4 via a filter circuit. Audio output from the detector is coupled through C74 to the base of the Audio Amplifier (TR7), which is an OC71.

TR6 is introduced for CW reception, providing a locally generated carrier amplified by TR5 and applied to the detector. The beat frequency is adjustable via the pitch control C70. TR6 is supplied by zener diode D3.

An audio filter (L18/C76) is included between TR7 and the Audio Driver (TR8, OC83), resonated at approximately 1,000 c/s for CW reception. This filter can be switched out for AM signals.

The push-pull Output Stage operates in Class 'B', providing 3W output to the internal loudspeaker. Low impedance telephones can be plugged into a panel socket, which interrupts the speaker output.

Installation

Batteries: The EC10 is supplied without batteries. Six standard 1.5V dry cells are required. Leak-proof types are recommended. Other suitable batteries include Vidor U2, Oldham V0002, Drydex T20/T21, Siemens BA6103, Pertrix K532, and Rayovac 601. NATO Stock No. 6135-99-910-1101. To fit batteries, unscrew two knurled screws at the rear, lift the battery box, disengage the four-way connector, remove the inner cover, sort batteries into two groups of three, and slide them into the troughs. Use the diagram on the container and ensure correct polarity; incorrect connection can damage transistors.

Aerial Connections: Sockets are provided for short rod aerials, single wire aerials, and balanced or unbalanced transmission line feeders. Single wire aerials connect to the "Al" socket with a special shorting plug between "AE" and "EARTH". This plug is also used for coaxial feeders (braid to "EARTH", inner conductor to "Al") or short rod aerials. For balanced feeders, remove the shorting plug and connect feeder wires to "AE" and "Al". The shorting plug can be temporarily inserted into the "A2" socket to avoid loss. The "A2" socket is for short rod aerials when a full-size aerial is not available and is not suitable for resonant loaded whip aerials.

A good earth connection can improve results and reduce locally generated noise.

Telephones: Telephones or an external loudspeaker can be connected to the panel socket. The output is matched to 3Ω and provides satisfactory results with telephones up to 600Ω impedance. Higher impedance may be used with reduced output and quality.

Operation

Operation is straightforward. The SUPPLY switch is ganged to the RF GAIN control and is engaged by rotating RF GAIN clockwise. Tuning is performed with the large knob on the right, featuring a precision geared drive with flywheel loading for smooth, rapid movement. The dial is calibrated in Mc/s (except Range 5, which uses kc/s) and has range numbering. The WAVECHANGE switch is located to the left of the TUNING control.

A calibrated vernier scale above the TUNING control, used with the bottom logging scale, provides an arbitrary frequency reading that can be recorded for re-setting. Four push-button switches control:

• AF FILTER IN/OUT
• BFO ON/OFF
• AGC ON/OFF
• DIAL LIGHTS ON/OFF (mechanically biased to 'off', must be held 'on')

The DIAL LIGHTS consume significant current and should be used only when essential. The BFO PITCH control is for CW reception, allowing adjustment of the beat note. For CW, AGC is typically switched 'off' and RF GAIN reduced to prevent overloading. For AM, AGC should be 'on' and RF GAIN advanced to maximum.

Maintenance

Routine maintenance is minimal, primarily battery replacement. For faults, the cabinet can be removed by unscrewing retaining screws and disengaging the battery connector. The cabinet slides away from the panel.

Dial Bulbs: Replacement bulbs should be L.E.S. type, rated at 6V, 50mA.

Instructions for re-stringing the drive cord: If the pointer drive cord breaks or slips, follow these steps carefully:

1. Remove existing cord; set tuning gang to full mesh.
2. Tie a double knot on one end of the new cord, feed through the left-hand drive pulley hole (approx. "4 o'clock").
3. Wind cord 1.5 turns anti-clockwise around the drive pulley, then pass under/over the left-hand guide pulley.
4. Pass cord across dial left-to-right. While holding tension, rotate tuning control to fully unmesh the tuning gang (approx. 3 turns on the left-hand drive pulley). Maintain tension.
5. Pass cord clockwise around the jockey pulley (right side), then back to the right-hand drive pulley. Feed into pulley groove and through the hole (approx. "10 o'clock"). Mark cord where retaining knot should be tied when jockey pulley rim aligns with panel handle screw.
6. Free cord from jockey pulley, maintain tension, and draw through the right-hand drive pulley until tight on the left-hand guide pulley.
7. Tie knot at the marked position and cut surplus cord. Feed back and replace around jockey pulley.
8. Set tuning gang to full mesh, slide pointer to 'O' on logging scale. Attach pointer to cord (ensure it passes under pointer carrier prongs) and check drive for free operation.

Re-alignment

Re-alignment should only be performed by individuals with knowledge of radio alignment procedures and appropriate test equipment. Sensitivity figures are based on new batteries and the cabinet removed.

Required Test Equipment:

• Signal generator(s) covering 465 kc/s and 550 kc/s to 30 Mc/s (30% modulation at 400 c/s, 50/75Ω output impedance).
• Crystal controlled harmonic generator (100 kc/s markers up to 7.5 Mc/s, 1 Mc/s markers up to 30 Mc/s).
• Output meter matched to 3Ω.
• Trimming tools: Miniature insulated screwdriver, small metal-tipped insulated screwdriver, Neosid Type H.S.1. hexagonal core adjuster.

Re-alignment of the IF Stages and BFO: Remove IF printed wiring board screws, rotate board 90° vertically, and re-insert two screws. Connect generator output to Range 5 Mixer coil (L11) with 50Ω source. Disable Local Oscillator by shorting C48. Connect output meter to the telephone socket. Set receiver controls: Range Switch to Range 5, Tuning to 560 kc/s, RF/AF Gains to Maximum, AGC/BFO to Off, Audio Filter to Out. Tune generator to 465 kc/s (30% modulation at 400 c/s). Set attenuator for ~50mW output. Peak IFT1, IFT2, IFT3 cores for maximum output. Re-check adjustments. Set attenuator for 50mW output; input should be ~4uV at 465 kc/s. For low IF sensitivity, investigate further.

With generator tuned to IF, switch off modulation, unplug meter. Set BFO pitch control to mid-travel. Check that clockwise rotation increases capacity. If necessary, re-set knob. With control at mid-travel, switch on BFO and adjust core in L17 for zero-beat. Check BFO control operation and disconnect generator and shorting link across C48.

Re-alignment of the RF Section: First, check overall calibration accuracy using the harmonic generator connected to "Al" and "AE" sockets (shorting link between "AE" and "EARTH"). Set generator to 1 Mc/s markers. With BFO on, tune across Range 1, checking scale accuracy at each megacycle point. Accuracy should be within 1% (e.g., 300 kc/s at 30 Mc/s). Re-alignment of the Local Oscillator should only be attempted if errors exceed this. Repeat checks for Ranges 2 and 3 using 1 Mc/s markers, then Range 4. Introduce 100 kc/s markers for Range 5 checks. If errors exceed 1%, perform normal tracking procedure using the provided tables for alignment frequencies and adjustments. Adjustments should be limited to ranges with excessive error, repeating adjustments to cancel interaction.

Alignment of RF (Aerial) and Mixer circuits: Disconnect harmonic generator, connect standard signal generator (75Ω for Ranges 1-4, 400Ω for Range 5). Re-connect output meter and switch off BFO. Adjustments are made at the same frequencies as oscillator alignment, using trimmers and cores listed in the second table. Repeat adjustments several times to cancel interaction.

Diagram Description:

• Plan View of Model EC10 Receiver: This diagram shows the top-down layout of components and wiring on the receiver chassis, illustrating the placement of coils, capacitors, transistors, and other parts.
• Underside View of Model EC10 Receiver: This diagram provides a view from the bottom of the receiver chassis, detailing the arrangement of components and connections on the underside, including the IF transformers and various wiring points.

On completion of adjustments on Range 5, tune receiver to 560 kc/s and generator to 465 kc/s. Increase generator output for an indication on the output meter, then adjust IF rejector coil L1 for minimum output. Re-tune generator to 560 kc/s, reduce output, and check alignment of L6 for maximum signal. Repeat checks at 465 kc/s and 560 kc/s, then perform a sensitivity check on all ranges.

Voltage Analysis

The voltage readings in the table below are useful for fault diagnosis. Readings are taken under "no-signal" conditions with controls set as specified. All readings are NEGATIVE with respect to chassis. The stabilised supply should be between 6.4-6.6V. A tolerance of 10% applies to readings taken with a 20,000Ω/V meter.

* Readings become 6.5V, 0-1V and 0V with RF Gain at min.

** Readings become 7.35V, 0.35V and 0.16V with RF Gain at min.

Control Settings for No-Signal Readings:

Spares

The following list details major spares for the EC10 receiver. Quote the Serial No. in all correspondence and direct enquiries to the "Sales and Service Dept."

Inductors, Transformers etc.

• L1: 465 kc/s IF Rejector coil
• L2: Range 1 RF (Aerial) coil
• L3: Range 2 RF (Aerial) coil
• L4: Range 3 RF (Aerial) coil
• L5: Range 4 RF (Aerial) coil
• L6: Range 5 RF (Aerial) coil
• L7: Range 1 Mixer coil
• L8: Range 2 Mixer coil
• L9: Range 3 Mixer coil
• L10: Range 4 Mixer coil
• L11: Range 5 Mixer coil
• L12: Range 1 Oscillator coil
• L13: Range 2 Oscillator coil
• L14: Range 3 Oscillator coil
• L15: Range 4 Oscillator coil
• L16: Range 5 Oscillator coil
• L17: Beat Oscillator coil
• L18: Audio Filter coil
• IFT1: 1st IF transformer (465 kc/s)
• IFT2: 2nd IF transformer (465 kc/s)
• IFT3: 3rd IF transformer (465 kc/s)
• T1: Audio Driver transformer
• T2: Audio Output transformer

Miscellaneous

• Range Switch Clicker mechanism
• Wafers S1a/c, S1e/f, S1g/h
• Wafers S1b, S1d, S1i, S1j
• Push Switch Assembly (S2-S5)
• RF Gain control (with switch)
• AF Gain control
• Dial bulbs (L.E.S. 50mA 6-7mm.)
• Dial bulb holders
• Phone jack
• Loudspeaker
• Aerial socket strip
• Earth terminal
• 3-gang tuning capacitor
• Flexible coupler
• BFO tuning capacitor
• Drive Assembly
• Pointer Assembly
• Dial glass (calibrated)
• Knobs (large)
• Knobs (small)
• Shorting plug (AE)

Errata

R24 should read: 1.5K, R35: 47K.

C10 should read 20pF.

Add C23a. 10pF Tubular Ceramic across tuned winding of L9.

D1 is shown reversed.

Add two DD006 diodes (parallel-connected with reverse polarity) across the "Al" and "AE" terminals. Allocate Reference D4 and D5.

Layout of IF Printed Board

Diagram Description: This diagram shows the physical layout of components on the IF Printed Board, indicating the placement of transistors (TR5, TR6), IF transformers (IFT1, IFT2, IFT3), capacitors, and other parts relative to their connections.

List of Component Values

Resistors (All 10% watt unless otherwise indicated):

Capacitors:

Model EC10 Mk. II Supplement

Introduction

The EC10 Mk. II is the current production replacement for the well-established EC10 Communication Receiver. It incorporates several additional features and has modified styling. Scale calibration is marked in kHz and MHz, aligning with standardised nomenclature. This supplement details modifications and should be used with the basic EC10 Instruction Manual.

Fine Tuning Control

A voltage variable capacitance diode (D6: BA111) is wired across the oscillator section of the three-gang tuning capacitor to permit fine tuning independently of the main tuning control. A potentiometer (RV3) varies the DC voltage applied to the diode. Fine tuning coverage varies by range but is compatible with the main tuning control. Typical frequency swings are 75kHz and 15kHz at the high-frequency ends of Ranges 1 and 3 respectively. For normal operation, the Fine Tuning control should be at its mid-travel position (index against mark) to allow adjustment up or down in frequency.

Carrier Level Meter

The built-in carrier level meter serves as a tuning indicator and for comparing relative carrier levels, with a scale calibrated in arbitrary divisions 0-10. It is controlled by the AGC voltage but operates normally irrespective of the AGC SWITCH setting. Maximum meter deflection indicates correct tuning.

Standby Switch

This control desensitises the receiver when set to "STANDBY", primarily for use with an associated transmitter. For normal reception, it must be set to the 'non-standby' position. Two spare contacts are available for connection to a transmitter control circuit for single-switch changeover facilities. Alternatively, the desensitising can be controlled from a spare switch section on the transmitter changeover switch, with the receiver STANDBY SWITCH left permanently 'non-standby'. An efficient aerial changeover relay is essential for installations using an associated transmitter.

Low-level Audio Output

This facility, present on late versions of the basic EC10 and the Mk. II, provides a rear socket for feeding a tape recorder or an external audio amplifier. The output is not affected by the receiver's AF GAIN control and should normally be set to minimum when using an external high-power amplifier. Volume control or recording level is managed by the external unit.

Telescopic Aerial Kit LP3126

A specially designed telescopic aerial is available for the EC10 Mk. II. Pre-drilled holes are provided at the rear for simple attachment. This aerial is intended for use when a normal shortwave aerial is not available, such as during occasional portable operation. A properly designed aerial system is strongly recommended for permanent installations.

Model EC10 Mk. II - List of Component Values

Capacitors:

Resistors (All 10% watt unless otherwise indicated):

Spares (Model EC10 Mk. II):

• Dial glass (calibrated) - D3188B
• Fine Tuning Control (RV3) 10,000 Ω 1in. law. - 7762P
• Carrier Level Meter (100uA FSD) - SKM69
• Audio Plug - 6943P
• Desensitising Switch (S7) - 7352P

Circuit Diagrams: The document includes detailed schematic diagrams illustrating the receiver's circuitry, including RF, IF, audio, control, and power supply sections. These diagrams show the interconnections of transistors, resistors, capacitors, inductors, and transformers.

Diagram Descriptions:

• Layout of IF Printed Board: This diagram shows the physical arrangement of components on the IF Printed Board, indicating the placement of transistors (TR5, TR6), IF transformers (IFT1, IFT2, IFT3), and associated components.
• Plan View of Model EC10 Receiver: This diagram illustrates the top-down layout of components and wiring on the receiver chassis, showing the placement of coils, capacitors, transistors, and other parts.
• Underside View of Model EC10 Receiver: This diagram provides a view from the bottom of the receiver chassis, detailing the arrangement of components and connections on the underside, including IF transformers and various wiring points.

Errata (Model EC10 Mk. II):

• R23 & R27 should read: 330 Ω
• C48a should read: 15pF

Manufacturers

Eddystone Radio Limited
Member of Marconi Communications Systems Ltd.
Alvechurch Road, Birmingham B31 3PP
Telephone: 021-475 2231
Cables: EDDYSTONE, BIRMINGHAM
Telex: 337081

Printed in England

Issued November, 1971