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Old 27th Sep 2022, 9:57 am   #1
Gianluca Flati
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Default Unknown Radio

Hi, I need of schematic diagram for repair. The name of this radio, may be "Signal model 741 b5". Made in Hong Kong. No internet information, mystery radio.
Please help me, thank you very much, Luca Rome Italy.
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Old 27th Sep 2022, 10:03 am   #2
paulsherwin
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Default Re: Unknown Radio

You are very unlikely to find service information for this radio. It appears to be a typical Hong Kong multiband radio from the mid 1970s.

They are much simpler internally than the styling would suggest, so not difficult to work on.
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Old 27th Sep 2022, 11:06 am   #3
hamid_1
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Default Re: Unknown Radio

This is quite a common multiband radio chassis, made in Hong Kong and sold under various brand names. I have one badged Elftone Globemaster

The Binatone Worldstar appears to use the same chassis in a slightly different cabinet - see here: https://www.radiomuseum.org/r/binato...ar_014451.html

You can buy the service data from this forum's sister site: https://www.service-data.com/section...4451-worldstar

Hopefully that should help. Most of the faults with these radios are caused by dirty waveband switches and volume / tone controls.
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Old 27th Sep 2022, 2:26 pm   #4
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Default Re: Unknown Radio

Thanks for that link Hamid, I didn't know we actually had service info here.
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Old 27th Sep 2022, 3:43 pm   #5
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Default Re: Unknown Radio

I think ive seen one under the Vantone name also
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Old 27th Sep 2022, 4:45 pm   #6
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Default Re: Unknown Radio

They used all sorts of brands, presumably as the importer wanted. I have a similar one (not identical) branded Toiyo (or is it Toyio?). American store chains had them badged with the store brand.
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Old 27th Sep 2022, 6:21 pm   #7
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Default Re: Unknown Radio

I had a set with a fibreboard case with a dial that implied it had more wavebands than it actually had.
Typically the scale below "FM" would be marked "Aircraft" and the one below that "Police".
Interestingly both these scales have empty descriptors which seems like a missed selling point.
I wonder if this was to satisfy some legal restriction in its intended market area.
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Old 27th Sep 2022, 6:39 pm   #8
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Default Re: Unknown Radio

It was standard practice to imply that these radios had more extensive coverage than was actually the case, including meaningless band descriptions (at least in the UK) such as 'Weather' and 'Police'. On the other hand, mine does appear to use AM detection on the air band, which many cheap multiband radios don't bother with.
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Old 27th Sep 2022, 9:28 pm   #9
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Default Re: Unknown Radio

Quote:
Originally Posted by rambo1152 View Post
I had a set with a fibreboard case with a dial that implied it had more wavebands than it actually had.
Typically the scale below "FM" would be marked "Aircraft" and the one below that "Police".
Interestingly both these scales have empty descriptors which seems like a missed selling point.
I wonder if this was to satisfy some legal restriction in its intended market area.
The set shown was intended for the US market! All the frequencies shown are for NA, US and Canada.
Dave, USradcoll1
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Old 28th Sep 2022, 9:05 am   #10
paulsherwin
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Default Re: Unknown Radio

I think it's simpler than that Dave. They just based the design (particularly the tuning scale) on American world radios of the late 60s like Zeniths. They did get exported to NA, but they turn up all over the world.

We saw a lot of HK radios in Britain because it was technically part of the British Empire until 1997 (the last significant place to be so). The use of the 'Empire' concept had largely ended in the 1950s in Britain itself, but HK manufacturers continued to refer to their products as 'Empire Made'. I think they paid lower UK import duties.
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Old 28th Sep 2022, 1:07 pm   #11
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Default Re: Unknown Radio

There were variations of these radios. Looking more closely, the Binatone Worldstar has Long Wave but the OP's radio has Marine Band (MB) instead. The Binatone PCB is marked Model No 741 - the same number as the OP's radio. Therefore I concluded they are the same radio with minor changes to suit the intended market.

In the 1970s and 80s, Hong Kong manufacturers were very successful at producing low-priced electronic goods like radios and digital watches for export worldwide. Nonetheless, errors sometimes crept in. Some of these multiband radios sold in the UK have American frequencies marked for Police and Weather which did not apply over here. Nobody seemed to care much, though.

Since Britain handed Hong Kong back to China in 1997, we no longer see goods marked "Made in Hong Kong". It's all made in China now. I believe the manufacturing industry has moved to mainland China and Hong Kong is now just a financial and business hub.
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Old 28th Sep 2022, 1:23 pm   #12
Gianluca Flati
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Default Re: Unknown Radio

Thanks a lot to everyone.
Good Luke, Luca Rome Italy.
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Old 29th Sep 2022, 9:35 pm   #13
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Default Re: Unknown Radio

I've never seen a set of this class with a squelch control before.
Did anyone else spot that?
I wonder how well it works?

Quote:
Originally Posted by paulsherwin View Post
On the other hand, mine does appear to use AM detection on the air band, which many cheap multiband radios don't bother with.
I doubt if there is any VHF/FM - VHF/AM discriminator/detector switching.
More likely no IF limiting, and a lousy discriminator circuit that didn't
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Old 30th Sep 2022, 9:39 am   #14
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Default Re: Unknown Radio

FM performance is actually pretty good on my example, with nice clean sound. I've never tried tracing out that part of the circuit though.

Squelch controls were common on these, and they do sort-of work, but they aren't much use.

Overall the electronic design is very conservative, with standard circuits used throughout. It's a pity about the "sheep in wolf's clothing" styling and marketing in a way, as they are perfectly usable radios despite people tending to view them as a joke. I'm sure lots of kids had fun exploring SW with them in the 70s.
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Old 30th Sep 2022, 7:16 pm   #15
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Default Re: Unknown Radio

The other thing I associate with this style of radio, at least the one I had, mains/battery with a fibreboard case, is the crude battery charging feature. A "charge" switch and indicator light. As "D" size nicads were expensive and specialist items, not yet available on the High St, I've always assumed the intention was to charge "normal" HP7 cells.

Attempting this was not unknown, and it would be interesting to see a circuit to see if the often recommended "Dirty DC" technique was used.
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Old 1st Oct 2022, 8:42 am   #16
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Default Re: Unknown Radio

Hi

I still have the Binatone Worldstar version of this set, which seems to work much better than it has a right to. A quick search revealed that Manuals and Circuit diagrams are freely available online.

It was rather ingenious of the designers to equip it with two separate front ends, one for 88 to 108 MHz "FM" and another for 108 to 174 MHz "VHF". The dial cord wraps round two tuning drums, and the 10.7 MHz IF output coils are just summed by putting them in series. This relegates band switching to DC and saves all the difficulties of alignment and switching coils at VHF.

Although "VHF" is tuned as one band, it enjoys no less than three printed tuning scales; Aircraft, Weather and High. All helps to look more impressive I suppose !

Looking at the detection arrangements, there is just one FM ratio detector for both these bands and the alignment instructions call for an FM modulated signal generator for both bands. This would have fitted with the use of FM in the USA for two-way and marine radio on the "high band" plus the weather broadcasts around 162 MHz. I guess the AM voice transmissions for aircraft on 118 to 136 MHz would have been a bit of an afterthought, with deliberate mistuning needed to resolve them. At least the "VHF" band has no AFC to spoil this workaround.

The squelch (only for the "VHF" band) has D10 and D11 as a level detector, with adjustable offset by R44 to set the threshold. This then gates the audio via Q9 and Q10. From memory it sort of works.

There is also D13 and D14 plus Q11 and Q12 as an IF level detector which drives a red "Tuning" LED D12. The LED sits in the tuning pointer which looks quite neat.
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Old 1st Oct 2022, 2:46 pm   #17
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Default Re: Unknown Radio

Regarding the Binatone Worldstar schematic, how is the signal detected on FM? The board layout might be a clue?

Unless I'm missing something?

Lawrence.

Last edited by ms660; 1st Oct 2022 at 2:50 pm. Reason: extra info
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Old 4th Oct 2022, 3:01 pm   #18
usradcoll1
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Default Re: Unknown Radio

Quote:
Originally Posted by hamid_1 View Post
There were variations of these radios. Looking more closely, the Binatone Worldstar has Long Wave but the OP's radio has Marine Band (MB) instead. The Binatone PCB is marked Model No 741 - the same number as the OP's radio. Therefore I concluded they are the same radio with minor changes to suit the intended market.

In the 1970s and 80s, Hong Kong manufacturers were very successful at producing low-priced electronic goods like radios and digital watches for export worldwide. Nonetheless, errors sometimes crept in. Some of these multiband radios sold in the UK have American frequencies marked for Police and Weather which did not apply over here. Nobody seemed to care much, though.

Since Britain handed Hong Kong back to China in 1997, we no longer see goods marked "Made in Hong Kong". It's all made in China now. I believe the manufacturing industry has moved to mainland China and Hong Kong is now just a financial and business hub.
I bought a receiver, similar to the one pictured at a swapmeet, that was intended for the UK market. The mains lead had a tag with the instructions to install a BS1363 plug.
The seller said that he connected the bare leads to 120V and it worked.
I figured that it worked on half voltage, it must be OK.
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Old 4th Oct 2022, 3:20 pm   #19
paulsherwin
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Default Re: Unknown Radio

They normally have quite simple unregulated power supplies, with just a transformer, a couple of diodes and a big electrolytic cap. A 240V one probably would work acceptably well on a 120V supply.
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Old 4th Oct 2022, 4:31 pm   #20
Restoration73
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Default Re: Unknown Radio

I acquired a red "Expo" HK radio with AM, FM, and AIR/PB. As it covers up to
175MHz I can use it to test a 174.5 radio mic that also came my way free.
I have scanned the schematic stuck inside.
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