Unknown pocket 6-Transistor Radio repair project - UK Vintage Radio Repair and Restoration Discussion Forum

granazis · 27th Mar 2024, 7:25 pm

I have a little pocket Transistor Radio that is not working.
Unknown make and model. It is a 6-transistor radio (see photos). The frequency selector indicates wavelength in metres: from 118 to 558m. It's probably from the mid 1960s. At the back there is a " British Crown Colony of Hong Kong" stamp. It takes a single 9V battery.
I originally got it for spares but now I think I can attempt to make it work.
Any idea how I can see if it can be repaired?

paulsherwin · 27th Mar 2024, 7:31 pm

It seems to be a pretty typical HK pocket radio from the mid 60s. They're usually simple standard 6 transistor designs but the size can make them difficult to work on. Just fault-find as you would with any dead radio. The electrolytics are often bad.

greg_simons · 27th Mar 2024, 7:48 pm

I'd put it a bit later, early seventies, very cut down job, only one if stage, can't quite determine if it's germanium or silicon transistors though.
Greg.

G6Tanuki · 27th Mar 2024, 8:02 pm

I'd say late-60s/early-70s; the coming of cheap and gainy Silicon Planar transistors [the technology originally developed by Fairchild in the early-60s but widely - and profitably - licensed] made these sorts of radios easy to produce.

The use of a transformer-coupled push-pull output stage shows the *design* to be an early one, but these continued in production well after the complementary-symmetry transformerless 'totem pole' became the norm in more-upmarket radios.

paulsherwin · 27th Mar 2024, 8:11 pm

HK AF amps almost always used driver and output transformers, long after transformerless designs became common.

Looking at it again, the styling does suggest 1970 or thereabouts, so it probably uses cheap NPN Si transistors.

G6Tanuki · 27th Mar 2024, 8:15 pm

Quote:

Originally Posted by paulsherwin

HK AF amps almost always used driver and output transformers, long after transformerless designs became common.

Yes, I guess once you're geared-up to produce them in their millions, and they're 'good enough' for the market, the business-case for redesigning to a totem-pole PNP/NPN output stage wouldn't be great.

Paul_RK · 27th Mar 2024, 8:23 pm

I'd go with late '60s, and I think you'll find the tuning range is in kc/s (kHz), roughly 550 to 1600, standard medium wave. Occasional models did use wavelength calibration, but in that case it would be something like 200-550m. Entry-level pocket set of the day, retailing at or around 39/6d.

Paul

MotorBikeLes · 27th Mar 2024, 8:30 pm

I see green transistors. In my experience, all the green transistors I have come across have been PNP silicon types. Could they just be exactly that, but using an earlier (PNP of course) germanium circuit?
Might be an idea to pull one out and see.
Les.

paulsherwin · 27th Mar 2024, 8:38 pm

That seems unlikely. PNP Si types cost significantly more than NPN at that time - that may be why they stuck with transformers. It's easy enough to switch to NPN with these simple designs, you just swap the polarity of the battery and all the electrolytics.

Sideband · 27th Mar 2024, 8:47 pm

It should be dead simple. In what way is it 'not working'? Connect battery, switch on. Is there a click or noise from the speaker? Yes....?The a.f stages are probably working. No?....check the on/off switch and the headphone socket...(the headphone socket cuts out the speaker and the internal switch contacts my be O/C). There...... a couple of quick checks that will take less than 10 minutes to get you started!

newlite4 · 27th Mar 2024, 9:08 pm

Easy way to date is to look for the civil defence arrows on the tuning dial, these will be at the 640 & 1240 kHz positions. Although generally used from 1953 to 1963, many radios still had CD marks for some time after and were not just used on radios for the American market since the tuning dials were generic.
The radio could just spring to life on its own after five minutes or so with a fresh battery. If the radio has not been used for many years it could take a short while for the electrolytic capacitors to reform.
Neil

paulsherwin · 27th Mar 2024, 9:15 pm

Most HK radios of this type were primarily sold in the UK, and didn't have US CD markings on the tuning scale despite being marked in kHz rather than wavelengths.

granazis · 27th Mar 2024, 9:30 pm

Quote:

Originally Posted by Paul_RK

I'd go with late '60s, and I think you'll find the tuning range is in kc/s (kHz), roughly 550 to 1600, standard medium wave. Occasional models did use wavelength calibration, but in that case it would be something like 200-550m. Entry-level pocket set of the day, retailing at or around 39/6d.

Paul

a 188-558 can only indicate "metres" That's why I think mid 60s, from the late 60s they used khz

Paul_RK · 27th Mar 2024, 10:15 pm

Quote:

Originally Posted by granazis

188-558 can only indicate "metres" That's why I think mid 60s, from the late 60s they used khz

If those are the markings, I'm sure you're right about wavelength calibration. My thinking was based on your original post where you said that 118m. was at one end of the scale.

Most of the Hong Kong pocket sets I've seen even from the very early '60s have frequency dials, so I think the style is more of an indicator of the age of the set than the wavelength-calibrated dial.

Paul

AD360 Rob · 28th Mar 2024, 10:10 am

I would first, clean contacts of the on/off switch and earphone socket (if fitted) next see if it draws any current. If so then the switch and at least some of it is operating. As has been mentioned if you get a click from the speaker and maybe some hiss then AF side is probably working. The main failing on these sets is the electrolytics which may reform to some extent of it is left powered on for a while. Check the fine wires from the ferrite rod aerial, they can fracture. A quick and easy check to see if the local oscillator is working is to use a second AM radio tuned to about mid band held close to the suspect set, tune the suspect set across the band and see if you can pick up any whistles on the other radio. If you can then the Local osc. is probably working. If not then you could be looking at transistor faliure. Unfortunately, little to no service information exists for these radios but as has been mentioned, they are relatively simple designs.

granazis · 28th Mar 2024, 1:25 pm

Quote:

Originally Posted by Paul_RK

Quote:

Originally Posted by granazis

188-558 can only indicate "metres" That's why I think mid 60s, from the late 60s they used khz

If those are the markings, I'm sure you're right about wavelength calibration. My thinking was based on your original post where you said that 118m. was at one end of the scale.

Most of the Hong Kong pocket sets I've seen even from the very early '60s have frequency dials, so I think the style is more of an indicator of the age of the set than the wavelength-calibrated dial.

Paul

Yes, for a example it has a "430" this cannot be KHz... I don't think that anyone in the 70s thought in wavelength terms (at least not the target audience for cheap pocket radios, ie younger people)
I have found photos of the back that are nearly identical like this: https://www.radiomuseum.org/images/r...8b_2639186.jpg which also has a "MODEL" on it. Or this https://www.radiomuseum.org/images/r...8b_2639188.jpg that also includes schematic, missing in mine but the other text is identical. These come from a (possibly) 1968 radio.
It may be one of those "7- transistor" radios. There something there looking like a transistor but different from the other 6.
Two have a very visible 148 - so they must be the common then BC148 - they also say USA - so the components aren't Japanese.
Here are some more pics. I took photos then took it apart - a fault is immediately obvious: the battery negative is not connected anywhere.
So the first thing will be to solder it and see if it works. Any ideas where it need to be connected?
Perhaps I can use as a guide the schematic in the photo photo of the link above.

granazis · 28th Mar 2024, 1:27 pm

Quote:

Originally Posted by AD360 Rob

I would first, clean contacts of the on/off switch and earphone socket (if fitted) next see if it draws any current. If so then the switch and at least some of it is operating. As has been mentioned if you get a click from the speaker and maybe some hiss then AF side is probably working. The main failing on these sets is the electrolytics which may reform to some extent of it is left powered on for a while. Check the fine wires from the ferrite rod aerial, they can fracture. A quick and easy check to see if the local oscillator is working is to use a second AM radio tuned to about mid band held close to the suspect set, tune the suspect set across the band and see if you can pick up any whistles on the other radio. If you can then the Local osc. is probably working. If not then you could be looking at transistor faliure. Unfortunately, little to no service information exists for these radios but as has been mentioned, they are relatively simple designs.

As one can see - now that I have opened it, the battery negative is not connected anywhere. Once I have found where it goes and solder it there it is certainly not going to work.
Thank you for the tip about checking the LO.

Paul_RK · 28th Mar 2024, 1:58 pm

Quote:

Originally Posted by granazis

I don't think that anyone in the 70s thought in wavelength terms (at least not the target audience for cheap pocket radios, ie younger people)

I think for a long time nearly everyone in the UK did - well into the 70s, perhaps into the 80s 247 meant Radio 1, 208 Luxembourg - and the changeover seems to have been driven by the demise of the UK radio industry, resulting in the market dominance of imported sets not designed specifically for the UK.

https://www.vintage-radio.net/forum/...ad.php?t=25670

Paul

paulsherwin · 28th Mar 2024, 3:00 pm

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.

granazis · 28th Mar 2024, 6:17 pm

Yes, the radio works! I connected the -ve to the PCB and it worked. Apparently though it should be connected to the on/off switch. The way I did it it doesn't switch off. Problem is that cables around the on/off switch are too cramped and cannot - at present - connect it there. I will try to find the correct place.
As for the origin, from what I have seen so far it must be one of the AITC/ITC pocket transistor radios made in the "British Crown Colony of Hong Kong" most likely between 1968 and the early 1970s. 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). Thank you all for the input and help!
Will try some "DXing" with it tonight!!

27th Mar 2024, 7:25 pm	#1
granazis Tetrode Join Date: Mar 2024 Location: Tandridge, Surrey, UK. Posts: 83	Unknown pocket 6-Transistor Radio repair project I have a little pocket Transistor Radio that is not working. Unknown make and model. It is a 6-transistor radio (see photos). The frequency selector indicates wavelength in metres: from 118 to 558m. It's probably from the mid 1960s. At the back there is a " British Crown Colony of Hong Kong" stamp. It takes a single 9V battery. I originally got it for spares but now I think I can attempt to make it work. Any idea how I can see if it can be repaired? Attached Thumbnails

27th Mar 2024, 7:31 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,988	Re: Unknown pocket 6-Transistor Radio repair project It seems to be a pretty typical HK pocket radio from the mid 60s. They're usually simple standard 6 transistor designs but the size can make them difficult to work on. Just fault-find as you would with any dead radio. The electrolytics are often bad.

27th Mar 2024, 7:48 pm	#3
greg_simons Octode Join Date: Jul 2004 Location: Evesham, Worcestershire, UK. Posts: 1,423	Re: Unknown pocket 6-Transistor Radio repair project I'd put it a bit later, early seventies, very cut down job, only one if stage, can't quite determine if it's germanium or silicon transistors though. Greg. __________________ Picture, sound?, DOOR.

27th Mar 2024, 8:02 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,010	Re: Unknown pocket 6-Transistor Radio repair project I'd say late-60s/early-70s; the coming of cheap and gainy Silicon Planar transistors [the technology originally developed by Fairchild in the early-60s but widely - and profitably - licensed] made these sorts of radios easy to produce. The use of a transformer-coupled push-pull output stage shows the design to be an early one, but these continued in production well after the complementary-symmetry transformerless 'totem pole' became the norm in more-upmarket radios. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

27th Mar 2024, 8:11 pm	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,988	Re: Unknown pocket 6-Transistor Radio repair project HK AF amps almost always used driver and output transformers, long after transformerless designs became common. Looking at it again, the styling does suggest 1970 or thereabouts, so it probably uses cheap NPN Si transistors.

27th Mar 2024, 8:23 pm	#7
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,260	Re: Unknown pocket 6-Transistor Radio repair project I'd go with late '60s, and I think you'll find the tuning range is in kc/s (kHz), roughly 550 to 1600, standard medium wave. Occasional models did use wavelength calibration, but in that case it would be something like 200-550m. Entry-level pocket set of the day, retailing at or around 39/6d. Paul Last edited by Paul_RK; 27th Mar 2024 at 8:35 pm.

27th Mar 2024, 8:30 pm	#8
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Unknown pocket 6-Transistor Radio repair project I see green transistors. In my experience, all the green transistors I have come across have been PNP silicon types. Could they just be exactly that, but using an earlier (PNP of course) germanium circuit? Might be an idea to pull one out and see. Les.

27th Mar 2024, 8:38 pm	#9
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,988	Re: Unknown pocket 6-Transistor Radio repair project That seems unlikely. PNP Si types cost significantly more than NPN at that time - that may be why they stuck with transformers. It's easy enough to switch to NPN with these simple designs, you just swap the polarity of the battery and all the electrolytics.

27th Mar 2024, 8:47 pm	#10
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,582	Re: Unknown pocket 6-Transistor Radio repair project It should be dead simple. In what way is it 'not working'? Connect battery, switch on. Is there a click or noise from the speaker? Yes....?The a.f stages are probably working. No?....check the on/off switch and the headphone socket...(the headphone socket cuts out the speaker and the internal switch contacts my be O/C). There...... a couple of quick checks that will take less than 10 minutes to get you started! __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

27th Mar 2024, 9:08 pm	#11
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,807	Re: Unknown pocket 6-Transistor Radio repair project Easy way to date is to look for the civil defence arrows on the tuning dial, these will be at the 640 & 1240 kHz positions. Although generally used from 1953 to 1963, many radios still had CD marks for some time after and were not just used on radios for the American market since the tuning dials were generic. The radio could just spring to life on its own after five minutes or so with a fresh battery. If the radio has not been used for many years it could take a short while for the electrolytic capacitors to reform. Neil __________________ preserving the recent past, for the distant future.

27th Mar 2024, 9:15 pm	#12
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,988	Re: Unknown pocket 6-Transistor Radio repair project Most HK radios of this type were primarily sold in the UK, and didn't have US CD markings on the tuning scale despite being marked in kHz rather than wavelengths.

28th Mar 2024, 10:10 am	#15
AD360 Rob Hexode Join Date: Jun 2012 Location: Chester, Cheshire, UK. Posts: 421	Re: Unknown pocket 6-Transistor Radio repair project I would first, clean contacts of the on/off switch and earphone socket (if fitted) next see if it draws any current. If so then the switch and at least some of it is operating. As has been mentioned if you get a click from the speaker and maybe some hiss then AF side is probably working. The main failing on these sets is the electrolytics which may reform to some extent of it is left powered on for a while. Check the fine wires from the ferrite rod aerial, they can fracture. A quick and easy check to see if the local oscillator is working is to use a second AM radio tuned to about mid band held close to the suspect set, tune the suspect set across the band and see if you can pick up any whistles on the other radio. If you can then the Local osc. is probably working. If not then you could be looking at transistor faliure. Unfortunately, little to no service information exists for these radios but as has been mentioned, they are relatively simple designs.

28th Mar 2024, 3:00 pm	#19
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,988	Re: Unknown pocket 6-Transistor Radio repair project 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.

28th Mar 2024, 6:17 pm	#20
granazis Tetrode Join Date: Mar 2024 Location: Tandridge, Surrey, UK. Posts: 83	Re: Unknown pocket 6-Transistor Radio repair project Yes, the radio works! I connected the -ve to the PCB and it worked. Apparently though it should be connected to the on/off switch. The way I did it it doesn't switch off. Problem is that cables around the on/off switch are too cramped and cannot - at present - connect it there. I will try to find the correct place. As for the origin, from what I have seen so far it must be one of the AITC/ITC pocket transistor radios made in the "British Crown Colony of Hong Kong" most likely between 1968 and the early 1970s. 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). Thank you all for the input and help! Will try some "DXing" with it tonight!!