Unknown pocket 6-Transistor Radio repair project

[paulsherwin]

People in the UK carried on using wavelengths for a long time. When Radio 1 changed transmitter networks in 1978 it was rebranded 'Radio One 275/285' (the wavelengths) and that carried on until Talk Radio took over the frequencies in the late 80s.

Glad you have it working.

HK radios were often marked 'Empire Made' in the 60s and 70s. This was pretty much the only common reference to the (former) British Empire by then.

[Herald1360]

Originally Posted by paulsherwin

The transistors are almost certainly NPN silicon. They may indeed be American - the US majors had built up production by then, and were starting to dump large numbers on the market. In fact, many of them look like the legendary 2N2926, which was one of the first cheap jellybean general purpose transistors and dominated the hobby mags around 1970.

https://www.alldatasheet.com/datashe...SS/2N2926.html

Find the main decoupling electrolytic, which will probably be 100uF or so. The battery +ve connection will go to whichever PCB track goes to the +ve side, and -ve connection... you've guessed it.

Not only do the transistors look like 2N2926s, at least one of the "48" sleeved ones has a visible "2N" on its base flange so they're 2N something or others.

[Paul_RK]

Originally Posted by granazis

Although the wavelength dial remains a puzzle pointing to something earlier - I haven't seen a single example (when it comes to pocket radios of the 60s) with wavelength (188-556).

British-made pocket sets all had wavelength calibration, but most UK firms had ceased producing radios at that end of the market by 1964. Here's a Pye from the early '70s, a badge-engineered Philips, built in Singapore and still with wavelength markings. It's only very slightly larger than the average Hong Kong pocket set. G and P on the dial as well as L and M, hence probably intended for sale in France as well as in the UK.

[roffe]

This Sinclair looks to be the same radio.
https://www.radiomuseum.org/r/unknow...upreme_ga.html

[marceljack]

Originally Posted by Paul_RK

G and P on the dial as well as L and M, hence probably intended for sale in France as well as in the UK.

Yes, most probably sold in France under the Philips and Radiola brands.

[granazis]

Now the radio works well. It seems that it covers all the traditional broadcasting band: 180-560m. It is mostly for strong stations though... Without some "help" it gets well only TalkSport (at 300m) and Radio5Live (near 500m). That's it.
I can also hear Lyca radio around 200m (40 miles away, off topic: this stations sounds very strong in Paris 240 miles away).
Regarding other stations, it can receive Premier around 200m and, thankfully my favourite local hospital radio (210m, 1 watt only!) It sounds quiet (I have to turn up the volume to max) but good where I am from 6 miles away. And that's about it. I noticed that it's more sensitive in the shorter wavelengths than the long.
Without help ("help" meaning: an active antenna) it cannot get R. Caroline (which on most radios I have comes stronger than the local 1W).
With an active antenna, both, the local 1W and R. Caroline sound strong, as well all others and can get BBC4 around 400m.
And those are all the stations one can get on MW in my area. There is one more near 550m (Panjab Radio) but so far I haven't tuned to that - maybe because the radio is losing its sensitivity near the extreme longer wavelengths of the dial (556m).

[Station X]

Three posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=209832

[Andrew2]

With only one IF stage and a short ferrite aerial, I would expect it to be short of gain and lacking selectivity. If there's a strong signal close to 648 kHz, it may be 'burying' Caroline.

[paulsherwin]

I know Greg said it only has a single IF stage in #3, but it looks as if it has 2 to me. These HK sets used a very conventional 6 transistor superhet design - mixer/osc, 2*IF, driver, 2*output.

Pulling in Caroline in that location is a big ask for any basic domestic radio though.

[Paul_RK]

Originally Posted by paulsherwin

Pulling in Caroline in that location is a big ask for any basic domestic radio though.

I wouldn't have thought that - isn't Caroline still broadcast from Mersea Island or thereabouts, only some 80 miles from Tonbridge? Its distance from Fakenham is similar, and Caroline comes in loud and clear on any six-transistor pocket set here.

Paul

[paulsherwin]

It certainly doesn't make it to Oxford, which is a similar distance. It's only supposed to be serving the eastern side of East Anglia with a tiny transmitter.

[Station X]

Originally Posted by Paul_RK

I wouldn't have thought that - isn't Caroline still broadcast from Mersea Island or thereabouts, only some 80 miles from Tonbridge? Its distance from Fakenham is similar, and Caroline comes in loud and clear on any six-transistor pocket set here.

Paul

Radio Caroline's MW transmitter is located at the old BBC World Service site at Orfordness, Suffolk.

[granazis]

Originally Posted by paulsherwin

I know Greg said it only has a single IF stage in #3, but it looks as if it has 2 to me. These HK sets used a very conventional 6 transistor superhet design - mixer/osc, 2*IF, driver, 2*output.

Pulling in Caroline in that location is a big ask for any basic domestic radio though.

All my AM radios receive R. Caroline on 648 very well
throughout the house, with their internal antennas. Including the recently revived Vidor. And it's signal is stronger than the local - 6 miles away - 1W hospital radio.
Yet in this case, while this radio receives the local hospital radio - which is crammed between Premier on 1413 and Lyca on 1458 ( meaning that selectivity isn't an issue) - it doesn't get R. Caroline. Well it didn't, today I got a faint signal but it isn't listenable.
Of course with the (indoor) active antenna both stations come strong!

[paulsherwin]

Fair enough, I stand corrected. AM reception can be very unpredictable and depends on many factors, not just distance.

[G6Tanuki]

Given the usage of these sort of radios, it may have been dropped (more than once) and this can displace the antenna coil on the ferret rod, causing misalignment which will be more noticeable at the lower frequency end of the tuning.

[granazis]

Originally Posted by paulsherwin

Fair enough, I stand corrected. AM reception can be very unpredictable and depends on many factors, not just distance.

The whole affair gave me a "wicked" idea though!
I have a shrill sounding transistor radio, and the recently restored mid-range audio Vidor. So I said "why not, let's see if i can have R. Caroline in (in)"glorious" pseudo-stereo.
So I put the small transistor radio at the one corner of the room and the Vidor at the other... it does have a pseudo-stereo sense.
But then I thought, how I can have some decent bass? Out came my R900 that has good AM/MW bass. I put that on the floor.
So now I have a quasi-HiFi "system" made of of two or three radios, each covering different audio frequency ranges:
- the small transistor radio acting as a twitter on the left, and a little closer , the Vidor as a normal speaker, and a little further so to create a little time delay, on the right and in the middle on the floor the R900 paying the role of the sub-woofer... A kind or 3-channel pseudo-stereo 3.1 for the vintage AM listening experience! Playing R. Caroline...

[Herald1360]

Originally Posted by paulsherwin

I know Greg said it only has a single IF stage in #3, but it looks as if it has 2 to me. These HK sets used a very conventional 6 transistor superhet design - mixer/osc, 2*IF, driver, 2*output.

Pulling in Caroline in that location is a big ask for any basic domestic radio though.

It does look very much like the Sinclair set in the RM link which has only one IF stage. The sixth transistor is simply the detector diode.

There do appear to be only two IFTs, the third smaller can would be the oscillator coil.

[paulsherwin]

Yes, that's possible. I didn't look to see if there was a diode anywhere.

[granazis]

Originally Posted by paulsherwin

Yes, that's possible. I didn't look to see if there was a diode anywhere.

There is a diode although, as I don't have the schematics, and now I have put everything back, I cannot see if that is protection for putting the battery the wrong way or for detection and demodulation.

[paulsherwin]

Reverse polarity protection is unlikely in this sort of radio. It looks like a detector.