HRSA EDDYSTONE 730/4 General Coverage Receiver Instruction Manual
- June 12, 2024
- HRSA
Table of Contents
HRSA EDDYSTONE 730/4 General Coverage Receiver Instruction Manual
Instructions
THE 730/4 general coverage receiver, made by Stratton & Co. Ltd of Birmingham 31, was in 1959 a very nice piece of equipment. Indeed, by today’s standards it is still a very nice receiver to drive. Yes, it is valved; yes, it does weigh a ‘tonne’, but nevertheless it still has a feel and a quality that makes tuning around the bands very much of a joy with this set. It is one of a number of Eddystone receivers of its era, all of a similar styling, covering frequencies up to the gigahertz range.
The set uses 15 valves, and has two RF stages of amplification, two IF stages of amplification, stabilised HT for VFO and BFO, audio filter, crystal IF filter, crystal calibrator and a noise limiter. The set tunes from 480kHz to 30MHz in 5 bands, and is a single conversion superheterodyne with an IF of 450kHz. The oscillator is on the high side of the received frequency. The actual coverage for each band is:
Band | 12.3-30.00MHz
Band 2 5.3-12.5MHz
Band 3 2.5-5.7MHz
Band 4 1.11-2.5MHz
Band 5 480-1100kHz
The valve types used are as follows:
6BA6 VI (RF amp. 1), V2 (RF amp. 2),
V5 (IF amp. 1), V6 (IF amp. 2),
V12 (BFO)
6BE6 V3 (Mixer)
12AU7 V8 (Audio pre-amps I & 2)
6AM6 V4 (local osc.), V10 (crystal calibrator)
6AMS5 V15 (audio output)
6ALS V7 (detector/AGC),
V9 (S-meter/noise limiter)
6AU6 VI (IF amp. (output feed))
5Z4G V13 (double diode rectifier)
VR150/30 V14 (voltage regulator)
The general appearance of the set is in the traditional Eddystone die-cast case, fluted sides, large chromed grab-handles the full height of the set at each end of the front panel, with large, easy to use, black knobs. The slate grey case is contrasted by a black scuff panel behind the knobs and controls, each control identified with silver lettering. The Eddystone badge takes pride of place in the upper centre of the front panel.
The tuning scale is nearly the full width of the receiver. It is large and rectangular, with a moving vertical cursor and a logging scale that appears in a centre window cut-out. The band in use is indicated by one of a vertical row of miniature bulbs to the right of the dial area. Two large black knobs are centrally located, one for band selection, the other main tuning, a large flywheel inside ensuring a very smooth tuning action. The remaining controls are fitted with smaller black knobs or comprise chromed toggle switches. The two stages of RF amplification are AGC-controlled to the g pins, with the manual RF gain being in the cathode leads of the two RF stages and the second IF stage
DISCLAIMER AND WARNING
This official Newsletter of the Historical Radio Society of Australia Inc.
often contains articles, circuitry and advice regarding mains-operated valve
radios and associated equipment. To operate, such appliances require high
voltages at lethal levels and as a consequence can constitute a serious risk
which could conceivably result in electrocution. Any | modifications
alterations and/or servicing of them must only be attempted by qualified
persons. In addition, an isolation transformer must be used at all times AC-DC
appliances are connected to the mains power supply.
The Historical Radio Society of Australia Inc. uses special care and diligence
in the preparation and selection of all material appearing in Radio Waves BUT
it is not responsible or liable for any loss or injury as a result of any
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The IF stages, also having AGC applied to them, have variable IF transformers along with the crystal filter to give a wide range of selectivities for different modes of reception. There is a four-position switch that alters the coupling of the IF transformers to affect the selectivity. A ‘phasing’ knob brings the crystal filter into operation and these two controls, along with the switchable audio filter, afford a high degree of choice in the range of selectivity available. Indeed, it takes some practice to obtain the best from these three controls.
The IF bandwidths with the different settings are approximately:
widest setting 10kHz at -3dB
first reduction 4kHz at-3dB
second reduction 2kHz at-3dB
max. reduction 1.3kHz at -3dB
max. red. + xtal filt 0.5kHz at -3dB
These figures are estimated from the IF response curves in the manual
The BFO and crystal IF phasing controls are unusual in that, with the BFO tuning control fully anticlockwise and the phasing fully clockwise those functions are off; tuning the BFO tuning knob clockwise brings the BFO into operation, turning the phasing knob anticlockwise activates the crystal. The supply volts are permanently connected to the BFO, the tuning capacitor effectively being shorted out when turned anticlockwise past a pre-set point.
The audio output is transformer-coupled to 2.5 and 600C2 sockets on the rear apron. A front-panel mounted ‘phone jack, high impedance, disconnects the loudspeaker (low impedance) output when used. Also available on the rear apron is a low-impedance IF 1ake i off, for use with such items as a panoramic adapter. A rear-mounted variable resistor allows the brightness of the dial lamps to be adjusted
The 500kHz crystal calibrator is operated by a push button on the upper left front of the receiver. The position of the dial cursor can be adjusted by altering a small knurled knob situated on the upper right of the front panel.
The set was designed for mains operation, 110 or 230 volt 50/60Hz, consuming 80 watts. A multi-pin plug assembly on the rear apron allows an external supply to be used.
SERVICING THE SET
The cabinet is removed after four large screws on the rear of the set are
released. An initial check that all the valve heaters are alight and that the
VR150/30 is emitting a violet glow can be easily made Unless one is skilled in
the alignment of receivers, in which case you probably will not be reading
this, it is unwise to judge the effects of adjustments by ear alone.
The alignment assumes therefore that a signal generator (450kHz to 32MHz with
30% AM modulation) is available, along with some form of test meter capable of
measuring watts at audio frequencies. A multimeter measuring volts across a
resistor fitted to the speaker terminals will give an indication though.
IF amplifier
Due to the complexity of the IF stages a wobbulator is recommended for any serious alignment work. It is unlikely that a fault will develop within the IF transformers, and adjustments of these should not be disturbed unless absolutely necessary. For checking purposes the following figures are given, all leads connected in the set, so therefore not strictly true ones but quite adequate for comparison. Test condition: RX Range 5, AGC & NL OFF, Pitch OFF, Xtal Phase OFF.
Selectivity Maximum, RF gain Maximum. Signal | generator 30% modulation, direct output. 50mW output | at speaker terminals for 11 mV at grid 1 of V6, or | 220mV at grid 1 of V5
To measure the overall sensitivity of the IF amplifier at the grid of V3 (frequency changer), will require unsoldering the lead at point X marked in the underneath view shown. The signal generator is injected at this point, 20uV input should give S0mW at the speaker terminals.
Oscillator alignment
All receiver controls are left as for the IF check. A crystal oscillator or the internal crystal calibrator, if known to be correct, should he connected to the aerial terminal. Set the receiver to range 1, BFO to centre position, and check calibration at 28MHz and 14MHz. To allow for subsequent calibration adjustments ensure the vernier pointer is set at the mid-point of its travel.
If the 28 and 14MHz points are appreciably off then correct the 14MHz calibration by adjusting range 1 oscillator core. The 28MHz point should he corrected using the associated trimmer. The other bands follow the same pattern.
Trimmer Core
Range 1 28MHz 14MHz
Range 2 12MHz 6.0MHz
Range 3 5.6MHz 2.5MHz
Range 4 2.5MHz 1.2MHz
Range 5 1.0MHz 500kHz
RF alignment
Using the signal generator set to give 10uV, switch off the BFO, receiver on range | tuned to 13.3MHz, inject a 13.3MHz modulated signal into the aerial socket. Use the RF gain control to keep the S-meter needle on the scale. Adjust the cores only of the two RF coils and one frequency changer coi for that band. Tune for highest output on meter.
Next, tune set to 28MHz, inject 28MHz from generator and adjust the three appropriate trimmers. Repeat the above until no further improvement is possible. Using the same procedure repeat for the other ranges.
Trimmer Core
Range 1 28MHz 13.3MHz
Range 2 12MHz 6.0MHz
Range 3 5.4MHz 2.6MHz
Range 4 2.3MHz 1.2MHz
Range § 1.0MHz 520kHz
Always adjust the r7immers at the high frequency end of the band and the cores at the low frequency end.
Sensitivity
For a signal to noise ratio of 15dB, output 50mW:
AM signal modulated 30 % at 400Hz : better than SuV
CW signal ranges 1, 2, 3, 4: better than 1V |
CW signal range 5: better than 21V
GENERAL USAGE
Using the receiver is a joy. The large scale and the smooth tuning control allow easy progression through the bands. The variable ‘ selectivity, whilst taking some mastering, does allow the weakest of stations to be extracted from a pile-up. The considerable reduction of the tuning knob, 60 complete tums to cover the entire scale, means that even on the most cramged of th.e ranges, range 1, 12.3 to 3IMHz, there is sufficient movement of the knob to make station separation easy.
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