Zodiac Sagittarius BX16 (1960)

[Phil G4SPZ]

This little radio was kindly given to me by a friend, who had found it amongst piles of junk and magazines whilst clearing out the shack of a Silent Key. The set arrived literally in bits, held together with PVC tape, and whilst 1960s plastic-cased valve radios are not normally my ‘thing’, it was sufficiently unusual and different to be worth an attempt at getting it going again.

A little research revealed that Zodiac Radio were based in Paris, and the Sagittarius BX16 model was released in 1960. Some decent images are available here, but I was unable to find a schematic. However, this two-band, four-valve-plus-rectifier superhet is relatively simple, and as a few parts were missing I decided to trace out its circuit in an attempt to complete the jigsaw. My model is marked “Made in Italy” and appears to be specifically designed for the UK market, being wired for 230 volts only with no voltage selector, and having a Long Wave band covering 1,500 metres, plus a little either side, selected by a latching push button protruding from the rear of the case.

Mechanically, the chassis is made of very thin and relatively flimsy tinned steel plate. Numerous ground connections are made by simply soldering wires direct to the metalwork, and the general standard of construction is quite untidy. A previous owner had replaced the output transformer, but the volume control’s spindle was broken and the control knob was missing. The chassis is secured to the front panel by the volume control fixing nut plus a single self-tapping screw, which was also missing. Suitable substitutes were found from stock. At this point I traced out the circuit, which is remarkably simple, but a few design features are worth pointing out. I apologise for the poor quality of the schematic, but I have no access to CAD software and the circuit is shown more-or-less as I sketched it out, in pencil, from the chassis in front of me.

The live chassis power supply incorporates an autotransformer which provides three LT supplies, for dial lamp and heater circuits, plus an HT supply that measures a little over 130 volts AC, feeding a half-wave rectifier with reservoir and R-C smoothing which gives a low HT rail of around 120V DC. The five B7G valve heaters are wired in an odd series-parallel arrangement. No adjustable trimmers or padders are fitted, rudimentary tracking being achieved by the oscillator section of the two-gang tuning capacitor having fewer plates of a different shape providing a special law. A single adjustable oscillator coil gives MW coverage, in conjunction with a single winding of Litz wire on the ferrite rod antenna, and LW is selected by the double-pole switch marked “press for 1,500m” on the rear of the chassis, which switches a pair of additional capacitors across the tuning gangs. AGC is derived from the hot end of the volume control but is applied to the IF amplifier valve only.

The antenna coil on the ferrite rod had partially unwound, and was carefully repaired and secured in place. The track of the broken volume control measured 600k, and the nearest I had was 500k so its spindle was hacksawed to the right length and in it went. I replaced “that” capacitor, and a handful of other components that looked suspect or measured incorrectly, although most capacitors are of the polystyrene type and seemed OK. I fitted a new 2-core sheathed mains flex and rewired the single pole switch into the live side. Before switching on I tested the valves, most of which fortunately proved fine as the rectifier and output beam tetrode are the relatively obscure US types 35A3 and 50B5. The exception was the EK90 frequency changer, which had significant heater-cathode leakage, but fortunately I had an equivalent 6BE6 available.

With the ferrite rod lashed into the circuit and an external speaker connected, I applied power slowly through the variac and was rewarded with signals and nice-sounding audio, but accompanied by excessive mains hum, so I replaced the combined reservoir and smoothing capacitor with new components rated at 400 volts DC, which reduced the hum to an acceptable level. The oscillator coil was adjusted to bring the medium waveband roughly into line with the dial markings, and the LW switch brought in Radio 4 on 198kHz, conveniently at the same dial position as Radio 5 Live. The IF transformer cores were very tight, so I decided to leave well alone as the receiver seemed reasonably sensitive.

The dial lamp, which had blown, looked very much like a small wire-ended neon, but on measuring the voltage across it I got just over 3 volts AC, and concluded that it was originally an incandescent bulb. I had some 3.5 volt 150mA MES bulbs in stock, so after checking that there was sufficient space between the front panel and the tuning gang, I fitted an MES lampholder and a new bulb. Dial illumination is by total internal reflection via the Perspex spindle of the tuning knob, and actually looks quite effective in operation. Unfortunately there is a crack in the Perspex disc of the tuning knob, but it is not too visible.

The case is made of an off-white coloured soft thermoplastic, which remarkably was complete and undamaged. A good clean with baby wipes followed by an application of liquid antique wax polish brought this up quite well. I found some suitable screws and reassembled the radio, with some difficulty because whilst the rear part of the case is fixed by a single self-tapping screw into the chassis, there are two moulded plastic locating pegs which fit into holes in the rear of the chassis. One of these was out of alignment due to slight warping of the thermoplastic case, and took some fiddling with until it finally snapped home, but the assembled set feels very sturdy.

Power consumption is around 25 watts, most of which appears as heat from the output valve - many miniature output valves run incredibly hot, but this seems normal and the top of the thermoplastic case shows no sign of distortion after several hours of operation, so presumably the extensive ventilation slots are sufficient to let the heat escape.

The end result is a usable and very compact 1960s-style radio which looks surprisingly attractive, depending (of course) on the eye of the beholder! It is also small enough to be sneaked into the house without the XYL noticing...

[Brian R Pateman]

What a neat little set!

The circuit is reminiscent of the KB Minuet OB10 (down to some of the valves types). The KB uses a PCB though, rather than a chassis.

Some of the Minuet sets also have a tuning dial with a small filament lamp just like this.

Can we have some photos of the innards please?

[julie_m]

That's a cute little set, with good use being made of a light pipe, and what an interesting power supply arrangement! Bet there was also a 110 V AC/DV version, with a 560 Ω ballast resistance across the heaters of the rectifier and output valves and 22 Ω across the lamp, to make up the extra heater current for the 6V3 valves.

I'd also like to see some photos of the chassis, please ..... That tuner arrangement with the acrylic rod is intriguing!

[Phil G4SPZ]

Thanks for your interest, chaps. I'll have to dismantle the set again to take photos of the innards, and I'm at the NVCF tomorrow so I will do this next week and post a few more pictures.

[Phil G4SPZ]

As promised, here are a few images of the insides of the Sagittarius BX16.

The first picture shows the general above-chassis layout, with the mains auto-transformer on the left and the waveband switch protruding from the rear of the chassis. It switches two polystyrene capacitors across the tuning gangs to obtain LW coverage. Note the B7G valveholders fitted into holes clearly intended for larger B8A or B9A sockets, and the large round hole in the rear panel of the chassis, which was intended for the mains voltage selector, not fitted on this model. Like AJS, I'm guessing from the circuit and the valves that this design may have started life as a 110 volt ac/dc set, as the HT is only around 120 volts, with resistive droppers for 220-240 volt mains. It probably ran incredibly hot on 240 volts. This is the UK-only variant where the auto-transformer has been fitted, and the set runs fairly cool other than the output valve, which gets quite toasty. I'd be interested to hear from owners of other models.

The next image shows the underside, and in the dim light you may just be able to see the oscillator coil, top right, the only adjustable component in the RF stage. The pink silicone sleeving is my addition, to cover some of the original un-insulated bird's nest wiring! The third photo shows the tuning capacitor, with its oscillator section having fewer vanes than the aerial tuning gang and with shaped fixed vanes to create a special law and avoid the need for trimming and padding components.

In the last two photos I have attempted to show the MES lampholder which I fitted to replace the original wire-ended bulb. This is a snug fit, but the 100mA bulb itself can be replaced with care using a short length of plastic tube or sleeving of the right diameter to grip the glass globe. The front panel is totally light-proof, but the light is conducted by total internal reflection through the perspex boss of the tuning dial, and in dim light it is quite effective.

I'm not proud of the appearance of the chassis, but decided against a more extensive restoration due to the relatively low standard of the original assembly. The set looks OK from the outside though, and that's good enough for most viewers - except you lot, of course!

Thanks for everyone's interest.

[Brian R Pateman]

Thanks for posting the pictures Phil.

For a set from 1960 it certainly looks anachronistic. A clear example of having a design which delivers adequate results and making the most of it.

On a set of this type I would not have restored it to its original pristine condition either. I think that the marks of age give interest to a very basic set that was never designed to be working over 50 years after its birth date.

[Sideband]

Very neat and well restored. Have you any pictures of it in its original state?


Rich.

[SeanStevens]

A strangely cute radio
nice work




SEAN

[Phil G4SPZ]

Thank you very much for your kind comments.

Originally Posted by Sideband

Have you any pictures of it in its original state?

No, sorry Rich. It came in pieces - case, front panel, chassis with wires hanging everywhere and bits missing - all wrapped together with insulating tape. And, like in many cases, I never know whether a radio is going to turn into a restoration project, never mind a success story, until I've made some progress with it, by which time it's too late to go back and take the 'before' pictures! Apart from a good clean and polish with liquid wax, I did very little to the cabinet, which fortunately was complete and undamaged.

I will take 'before' photos of everything that comes in from now on. Oops... I've spent today restoring a KB Rhapsody PP31/1 transistor portable, and guess what... no 'before' photo. That set arrived in bits, too...

[Phil G4SPZ]

Quite coincidentally, I've just been looking at a YouTube video here posted by W9RAN, and the radio in question looked remarkably similar to my Zodiac Saggitarius BX-16. The type of circuit was apparently known as the "All-American Five" marketed under several brand names as a cheap and cheerful MW table radio using five US-style B7G miniature tubes (...er... valves, sorry, got carried away there ) with heater voltages which added neatly up to 120 volts.

Apart from slightly different heater voltages, the valve line-up is very similar and I can now see that the Zodiac is a Europeanised copy of the AA-5, fitted with an autotransformer.

I assure you I won't be trying the same modifications that W9RAN suggests. Not on this radio, anyway...

[Jimmyhaflinger]

looks like this radio has an italian made "Faital" speaker

[Phil G4SPZ]

Thanks for that info. Not a common brand name over here. Although it's an apt name for a speaker used within a radio where high voltages are present and may be 'Faital'

[Kevin Hoyland]

Hello Phil.
Outstanding work has you always do.
Regards
Kevin.

[Phil G4SPZ]

Thanks, Kevin, you're very kind.