Model V5 Amenities Receiver

INTRODUCTION

The Australian Sound Systems Model V5 is an amenities receiver used by the Armed Services. It has a rugged steel case, with a steel front and back panel, using feet on the bottom and a chrome carry handle. There is a strip on each side to allow the case to be bolted down. It is a five valve superheterodyne receiver and operates from 6 volts DC. It has one RF (Radio Frequency) amplifier stage, two IF (Intermediate Frequency) amplifiers, but has no BFO (Beat Frequency Oscillator) so it is not intended to receive morse. This radio has octal valves, and is dated 1942. It has two frequency bands, the broadcast band, and a short wave band.

An "Amenities" receiver is intended to provide radio news and music to off duty serviceman. In the USA it was known as an "Entertainment" receiver, or called a "Troop Morale" receiver. In the UK it was known as a "NAFFI" receiver because it was placed in the canteen, and also known as an "Invasion" receiver because that is where you would hear of the invasion landings. This type of receiver is normally a ruggedised version of a domestic receiver, with the additional ability to operate from several voltages, and in hostile climatic environments.

V5 Front View

CONTROLS

The front panel layout has a speaker on the left hand side, and the dial on the right hand side, above three knobs. Below the knobs is the coil box. The controls are very simple. The left hand knob is the VOLUME control, the centre knob is the TONE control, and the right hand knob is the station TUNING knob. On the far left hand side at the top, is a push button, to turn the dial light ON. Below that, is the power toggle switch labeled ON and OFF. Again below that is a lifting handle. Finally at the bottom, the DC power leads come out the front and have two alligator clips which are used to fasten on to battery terminals. The coil box is at the bottom right. To change the frequency band, you have to remove the coil box, rotate it and plug it back in, upside down. It is held in by two chrome knurled screws. On the far right hand side is another handle, and the aerial terminal is below this. There is one lifting handle on the top.

V5 Top View

DESIGN

The radio itself has a conventional steel chassis which is cadmium plated, holding the five octal valves. There has been a lot of attention applied to tropic proofing and shielding. There is a round steel box underneath each valve, and it has a round lid. Inside each box are the components for that valve. Near the chassis end, several capacitors are inside a square can (looks like an IF transformer) and this is pitch filled. The valves have snugly fitting “GOAT” shields, and a strange spiral valve cap, like a coiled spring. The capacitor cans, the valve shields, and the valve cans are all soldered to the chassis. The capacitors are mica, electrolytic, and paper types. The resistors are the old wire end wrapped body/tip/dot style. It uses rubber wire, which is now brittle with age. The power supply uses a vibrator, and is in a separate closed box. There is no valve rectifier as it uses a synchronous vibrator, and a capacitor and resistor HT filter. The push button for the dial light, looks like a front door bell push. The valve filaments are connected in a series parallel arrangement, with bypass capacitors.

The radio is a superhetrodyne type and has one RF amplifier, and two 455 kHz IF amplifiers. It is also reflexed in the last IF amplifier and first AF amplifier (reflexing means that one valve functions as an IF amplifier, and at the same time, as an AF amplifier). The audio output valve is a 1L5 pentode which drives a large internal speaker. The TONE control is a 500 k ohm potentiometer from the grid to ground, with a capacitor to ground from the wiper. The audio pre-amplifier, IF amplifier, detector, and AGC (Automatic Gain Control) rectifier is a 1K7 pentode double diode. The first IF amplifier is a 1M5 pentode, and there are three IF transformers which are slug tuned with fixed capacitors. The mixer/oscillator is a 1C7. The RF amplifier is a 1M5. The receiver has AGC and this is applied to the RF amplifier, and the IF amplifier. The mixer has AGC only for the broadcast band. It uses a three gang tuning capacitor, with a right angle spring loaded gear drive.

V5 Underneath View

The case is made from steel, has a chrome metal handle on the top, two handles on the front, and rubber feet on the bottom. There are metal tie down straps on both sides of the cabinet. Radios like this were often shipped in their own wooden protective box, so this may have been to secure it in the transit box. The radio uses cadmium plated steel round screws, and but uses no lock washers, and many bolts are just crudely cut off with cutters. The front panel and case is steel, and painted black wrinkle. There is a small bag of dessicant, tied with string to the speaker transformer.

There are two small brass plates on the front of the speaker panel, one with the serial number and model, the other with the suppliers name, “SUPPLIED BY A. A. AMENITIES SERVICE”. The coil box has a chrome plate, with the makers name and address engraved and filled with red paint. Above this, is engraved a legend filled with black paint, “THIS SIDE UP FOR BROADCAST RECEPTION”. Below this is another legend for the shortwave band, but this is engraved upside down. When changing bands, you turn the coil box over, so the engraving is then the right way up.

RESTORATION

The radio was very dirty outside, with flaking paint and large rust areas, but the inside was very clean. It looked like it had never been touched, apart from one capacitor which had been replaced. The right angle drive to the tuning capacitor was loose and had a large amount of backlash. It was oiled and adjusted, and the dial pointer repositioned so that it traveled from end to end properly. The 8 inch permanent magnet speaker was seized, so it was removed, and a new one of the same vintage was fitted. It actually fell apart when it was removed, as the cone came completely out.

V5 Speaker in Two Pieces

The case, coil box, and front panel were sanded, rust converter used, masked with paper, then undercoated, and painted with black wrinkle paint. Any rusty screws were replaced or re-plated. The circuit diagram on the underside of the case was rusted away. I used a circuit that had been hand drawn by DP, thanks Dave. It is slightly different to my model.

V5 Circuit (courtesy Dave Prince)

V5 Rusty Circuit Under the Case

The front and top chrome handles were replaced by identical ones from a hardware store. The rusty alligator clips for the battery connections were replaced with new ones. The chassis was cleaned, and the knobs polished. The radio was reassembled.

V5 Painting

The coil box has several capacitors inside. One had actually expanded and cracked apart. All the four capacitors were removed, and re-stuffed with modern capacitors, so they look original. The coil box was reassembled.

V5 Cracked Coilbox Capacitor

V5 Coilbox Inside

The vibrator box was removed, and inspected. An electrolytic capacitor had leaked, and a run of acid was visible in the box. Luckily it had not escaped from the box. A mica capacitor had absorbed the acid, and it had swollen and split open, and both its connecting leads had rusted away. I replaced this with a new 1000 volt rated capacitor. One other paper capacitor across the transformer primary was also replaced. Both electrolytics were no good, one was open and the other was a short circuit, so both were replaced with 16 uF 500 volt capacitors. I attempted to power up the vibrator, but the input was a short circuit. I discovered a 0.1uF paper capacitor buried inside the pitch filled transformer. It was replaced. This time when powered up, there was no current drawn at all, some progress. I opened the vibrator and cleaned the contacts with sandpaper. Now, with a slight tap to the vibrator, it started buzzing, and I could measure some high voltage output, but it was negative 250 volts! I had reversed the transformer windings when I reinstalled it, so I changed them over, and the voltage was now positive. This interesting effect is only possible with synchronous vibrators. So all the five capacitors in the vibrator supply had needed replacing. The vibrator box was reassembled. I left the vibrator supply out of the radio, and did further testing and fault finding, using a bench supply for the high voltage.

V5 Vibratorbox Inside

I carefully checked all the valve filaments for continuity, as battery valve radios often have them damaged or burnt out. They were all good, so I then checked the connections. They proved to be correctly connected in the series parallel arrangement, so I carefully powered them up, with the vibrator supply removed from the radio. They drew the correct current, and the voltage distribution was correct. The dial light did not work, but the globe was good. The press button switch had a waterproof grommet over it, and this was a hard and would not flex. It could only be removed by breaking it away. The switch was dirty and stuck, so it was freed up. The dial light now worked when the button was pressed.

The rubber wiring was old and brittle, so I attempted to disturb the wiring as little as possible. The audio worked, but little else. There was no voltage on the IF valves, and this appeared to be an open resistor. A new one burnt up immediately. There were no obvious bypass capacitors, but they were tracked down to two above chassis square cans. Each had four capacitors in them, and connected to the appropriate places with long wires. After trying to isolate the capacitors and suffering broken insulation on the rubbers wires, I gave in and decided to replace all the capacitors in the two cans. The cans were removed from the chassis, and as they were soldered to the chassis, a 70 watt mains soldering iron was needed. The cans had the pitch removed, in our domestic oven. This filled the whole house with a pitch smell, but luckily I was alone at the time. I put new capacitors in the cans, and filled them with wax. The brittle rubber wires were thrown away and flexible rubber wire was salvaged from old mains cable. The cans were reinstalled, the burnt out resistors replaced, and now the IF amplifier worked. Any wires that I touched and broke, were replaced with flexible rubber wire. The thick main battery cables wires that ran externally were still flexible, thank goodness.

V5 Capacitor Cans

V5 Capacitor Cans refilled

The IF was aligned but one of the slugs in the last IF transformer did not move, and it had a broken slot on top where someone had attempted to force it. It was removed, and the slug slot fixed, but the plastic former broke. It was glued, and the transformer, aligned on the bench, then reinstalled. The flexible grid wire was hard rubber, so this was replaced. The spring top cap connections would not wet with normal solder, so silver solder was used. The IF aligned correctly at 455 kHz. One of the resistors on the AGC line physically fell apart, so it was replaced. There was the occasional loud bang due to a short circuit, as one of the coil terminals was very close to the chassis. This was probably due to whiskers, as after cleaning, it reduced, then finally stopped happening. Also, the coil terminal supplying the oscillator plate, shorts to ground, if the coil box is not inserted correctly, and this burns out the 5K resistor inside the coil box. This happened twice.

V5 Coilbox Terminals Close to Chassis

The radio was now receiving stations on the broadcast band. As I measured voltages at various points, the radio suddenly went soft. It was restored to full volume, by turning off and waiting a few seconds before turning back on. It appeared that the meter probe, if used in the RF or mixer stage, could cause a loud click, and this reduced the volume. It was eventually tracked down to the AF power output valve. The voltage on the grid, changed to positive 220 volts in the fault condition. I checked the coupling capacitor (even though it had been replaced), the grid resistor, the tone circuit capacitor, the potentiometer, but there were no faulty components. I used a megger to look for breakdown of the valve socket or valve base, as pin 4 had the screen voltage on it, and pin 5 was the grid. Nothing! I tested the valve, but it seemed to be fine, apart from lowish emission, but it was amplifying well with plenty of volume. In desperation, I tried a new 1L5 valve. The fault was gone. So the valve was the problem, even though it amplified well. Perhaps it was gassy.

The RF and mixer were aligned. To do this, you have to remove the back cover from the coil box, then remove a cover panel from under the chassis. Be careful, as the cover can slip, and touch the high voltage terminal on the coil box, and you can get a shock, as I did. You can then poke alignment tools into the coil box, with your fingers close to the high voltage. The broadcast band was slightly out but eventually aligned well. The shortwave band was a problem. It did not have a frequency scale or proper graduations. There were only the broadcast band graduations (extended down), and these had no relation to the frequency (Hz) or wavelength (Meters). They only had five areas, marked as station bands, but depending on which book you read, and the vintage, they may be different. The information I found, from two sources, showed:

16 meters 17.9-17.5 mHz
19 meters 15.6-15.1 mHz
20 meters 15.1-15.0 mHz
25 meters 11.9-11.6 mHz
26 meters 11.5-11.4 mHz
30 meters 10.0-9.9 mHz
31 meters 9.9-9.5 mHz
45 meters 6.8-6.4 mHz
49 meters 6.2-5.9 mHz

but none of these corresponded to the actual received frequency of the radio, which was actually 17.0-5.9 mHz. There was no oscillator adjustment slug or capacitor, in the coil box, so these must be factory set, and approximate only. As there was no oscillator adjustment easily possible, just the RF and mixer capacitors were adjusted. There were no slugs for them either.

V5 Dial Scale (no short wave frequency markings)

Consequently, the broadcast band is quite sensitive, but the shortwave band is ordinary. The sensitivity (for a 10 dB S/N)....
Broadcast band:
500 kHz = 3 uV
1500kHz = 1.3 uV

Shortwave band:
16 meters = 3 uV
20 meters = 3 uV
25 meters = 7 uV
30 meters = 6 uV
45 meters = 6 uV

The vibrator supply was reinstalled, and powered up. There was a large amount of vibrator noise. The filament 500 uF capacitors were found to low in capacity and were replaced. The radio draws 1.6 amps at 6 volts.

CONCLUSION

The radio performs well for a domestic receiver, considering it only has two IF stages and one RF stage, but is should perform better. It is easy to use, and fairly sensitive. The large speaker gives a good sound. The AGC is very effecitive, and the reflexing works well. The radio looks very rugged and professional, but on close inspection, many shortcuts and deficiencies are revealed. The TONE control functions in a strange way, and can almost be used as a volume control. The shortwave band needs to be calibrated in frequency rather than using the broadcast band scale and vague short wave station bands. The mechanical design could be better, and lock washers and correct screw length would help. It shows some effort of good shielding and tropic proofing, but let down by other aspects. The drilling of holes seems a little out of tolerance and poor alignment as the two name tags showed evidence of being hit with a hammer and screwdriver to straighten them. It would have been better if the circuit was located on the inside of the case, not on the outside. The terminals for the coil box need more clearance, to stop short circuits. Also, the radio should be turned off when changing the coil box, as the oscillator plate resistor may be burned out. Make sure that the coil box is tightly screwed in, to prevent movement, and possible shorts. Note that a capacitor in the coil box can hold a charge, and you can get a shock when handling the box, as I did. The RF and mixer alignment would be better from the front, by removal of the coil box nameplate. This radio had a surprisingly large number of faults, which is unusual. It is a fairly ordinary radio.

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