Concertona Tuning Cap - UK Vintage Radio Repair and Restoration Discussion Forum

poppydog · 29th Apr 2018, 3:15 pm

I have recently been repairing an Internet branded Concertona (Hong Kong) LW/MW radio. I cleaned the PCB with IPA as I was looking for bridged joints and inadvertently managed to get some into the tuning capacitor. The next day it was seized solid. To cut a long story short, its ruined. The combination of the IPA and the old solder flux I think has ruined the plastic between the plates. When I removed it and opened it up the plastic had gone like ham all floppy etc. there were pieces rolled up and bits missing. There is also an enormous amount of play on the shaft.

I have attempted to measure its capacitance and managed to get a figure of 98/198pf, how can I tell if this is right, if not what should it be? See pics. (apologies for the dirty nails, Molybdenum grease is a pain to get off

).

Regards
Poppydog

crackle · 29th Apr 2018, 5:00 pm

I have have some of these spare, my ones are about 20mm square and about 14mm between mounting holes centres, it is approximately 183 and 83 pf.
If it sounds any use send me a PM or email.
Mike

poppydog · 29th Apr 2018, 5:07 pm

Thanks Mike, that sounds promising, I will check the dimensions/spec of mine again and let you know in a bit.
regards poppydog

Refugee · 29th Apr 2018, 6:26 pm

Those caps are made of polystyrene and die if they come into contact with almost all solvents. Let it be a lesson learned.
I will await a photo of the set to see if it looks anything like my internet branded set.

vinrads · 30th Apr 2018, 4:43 pm

Ah! I wondered where the name ham radio came from. Mick.

poppydog · 30th Apr 2018, 7:23 pm

Mike (crackle) you have a pm.
I will put some pics up when its done, its nothing special. There was a whole heap of these internet brand radios on ebay before xmas, I managed to bag 1. Its more or less identical to the perdio burford
regards poppydog

poppydog · 5th May 2018, 8:31 pm

Tuning cap arrived and installed - a big thank you to Mike (Crackle).

I now have another problem. I have had it on for most of the day on MW, listening to Absolute. When I decided to switch it off I thought I would just make sure LW is still alright as I had had some tuning issues after fitting the new cap, when switched to LW there was nothing there, just a faint hiss

. I'd also replaced the wave band switch wires at the same time as the tuning cap so I thought it might have been something to do with this. After a lot of farting around it was eventually found that it was to do with voltage. The radio runs on 6v, the battery voltage had only dropped to 5.71v but for some reason LW won't work. Put fresh batteries in or connect it to my bench power supply at 6v and LW is fine. MW will work on a voltage down to around 4v.

Can anyone shed any light on this? I also have a Grundig Cityboy 400 that does this.

Regards
Poppydog

julie_m · 5th May 2018, 9:12 pm

The oscillator has to run at a lower frequency to pick up long waves. It's possible that the spent battery could be running out of steam before the inductor is fully charged with current, or the capacitor with voltage; thereby killing the oscillator.

poppydog · 5th May 2018, 9:19 pm

The 5.71v is measured with radio on, is 5.71v really a spent 6v battery? I was hoping to eventually run this on rechargeable AAs which I don't think would work with the radio like it is.
regards poppydog

julie_m · 5th May 2018, 9:55 pm

5.71V certainly isn't too shabby, no -- a radio should work with less. But if the set plays fine on LW with 5.71V from a bench PSU but not from the battery, suspect a weird fault with the battery like one cell going high-impedance to AC.

Is there an electrolytic capacitor wired across the battery (perhaps downstream of the on-off switch)? If so, try replacing it -- a bigger value will be fine. It's exactly the job of that capacitor to keep the oscillator going at low frequency, when there is the maximum energy in each cycle.

poppydog · 5th May 2018, 10:17 pm

The 5.71v was not from the bench supply, it was from the batteries under load, the 6v was from the bench supply and the fresh replacement batteries. There was a 500uf trojan cap after the on/off switch which wasn't soldered properly in the very beginning, upon testing it was no good anyway and was replaced with a 470uf
regards poppydog

julie_m · 5th May 2018, 11:10 pm

That was my understanding; but I meant, did you also try turning down the bench PSU to find the point at which the set cut out on LW? If the set works from the bench PSU even below 5.71V, then I would suspect a dodgy cell. A faulty cell could conceivably do strange things under a changing load, that will not show up on a simple multimeter test.

If there's a 1-10µF original capacitor near the oscillator section, try changing that.

This is one of those moments where you really need an oscilloscope .....

poppydog · 5th May 2018, 11:32 pm

What I will do is try it on bench supply, winding down voltage until lw stops. I ended up replacing all 3 of the electrolytic caps, the lower capacitance ones were very bad. I will also try some rechargeable batteries just to check, will look tomorrow.
The oscilloscope is out of the question im afraid unless I could find one that you could watch Baywatch on

regards poppydog

ms660 · 6th May 2018, 8:35 am

Check the transistors voltages, if ok try changing the transistor.

Lawrence.

poppydog · 6th May 2018, 10:07 am

Will have another look at voltages. The oscillator transistor has no markings on it so I will have to try to work out what it is, if a replacement is needed.
regards poppydog

poppydog · 11th May 2018, 7:58 pm

This one is all finished now, a replacement oscillator transistor was salvaged from a scrap hongkong radio pcb kindly sent to me by geoffk. After some minor adjustments to the tuning its very sensitive now, even on LW. The running voltages are now down to acceptable levels as well.

As I said its nothing special so won't appeal to many, but it is a nice Internet branded looking radio.

Quote:

Originally Posted by Refugee

Let it be a lesson learned.

Not going to get the buckle end am I?

Quote:

Originally Posted by Refugee

I will await a photo of the set to see if it looks anything like my internet branded set.

Some pics for you.

Regards
Poppydog

Refugee · 12th May 2018, 12:15 am

Mine is a smaller model with an all plastic cabinet.
Yours looks quite posh by comparison.

29th Apr 2018, 3:15 pm	#1
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Concertona Tuning Cap I have recently been repairing an Internet branded Concertona (Hong Kong) LW/MW radio. I cleaned the PCB with IPA as I was looking for bridged joints and inadvertently managed to get some into the tuning capacitor. The next day it was seized solid. To cut a long story short, its ruined. The combination of the IPA and the old solder flux I think has ruined the plastic between the plates. When I removed it and opened it up the plastic had gone like ham all floppy etc. there were pieces rolled up and bits missing. There is also an enormous amount of play on the shaft. I have attempted to measure its capacitance and managed to get a figure of 98/198pf, how can I tell if this is right, if not what should it be? See pics. (apologies for the dirty nails, Molybdenum grease is a pain to get off ). Regards Poppydog Attached Thumbnails

29th Apr 2018, 5:00 pm	#2
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Concertona Tuning Cap I have have some of these spare, my ones are about 20mm square and about 14mm between mounting holes centres, it is approximately 183 and 83 pf. If it sounds any use send me a PM or email. Mike

29th Apr 2018, 5:07 pm	#3
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap Thanks Mike, that sounds promising, I will check the dimensions/spec of mine again and let you know in a bit. regards poppydog

29th Apr 2018, 6:26 pm	#4
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Concertona Tuning Cap Those caps are made of polystyrene and die if they come into contact with almost all solvents. Let it be a lesson learned. I will await a photo of the set to see if it looks anything like my internet branded set.

30th Apr 2018, 4:43 pm	#5
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: Concertona Tuning Cap Ah! I wondered where the name ham radio came from. Mick.

30th Apr 2018, 7:23 pm	#6
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap Mike (crackle) you have a pm. I will put some pics up when its done, its nothing special. There was a whole heap of these internet brand radios on ebay before xmas, I managed to bag 1. Its more or less identical to the perdio burford regards poppydog

5th May 2018, 8:31 pm	#7
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap Tuning cap arrived and installed - a big thank you to Mike (Crackle). I now have another problem. I have had it on for most of the day on MW, listening to Absolute. When I decided to switch it off I thought I would just make sure LW is still alright as I had had some tuning issues after fitting the new cap, when switched to LW there was nothing there, just a faint hiss . I'd also replaced the wave band switch wires at the same time as the tuning cap so I thought it might have been something to do with this. After a lot of farting around it was eventually found that it was to do with voltage. The radio runs on 6v, the battery voltage had only dropped to 5.71v but for some reason LW won't work. Put fresh batteries in or connect it to my bench power supply at 6v and LW is fine. MW will work on a voltage down to around 4v. Can anyone shed any light on this? I also have a Grundig Cityboy 400 that does this. Regards Poppydog

5th May 2018, 9:12 pm	#8
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Concertona Tuning Cap The oscillator has to run at a lower frequency to pick up long waves. It's possible that the spent battery could be running out of steam before the inductor is fully charged with current, or the capacitor with voltage; thereby killing the oscillator. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

5th May 2018, 9:19 pm	#9
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap The 5.71v is measured with radio on, is 5.71v really a spent 6v battery? I was hoping to eventually run this on rechargeable AAs which I don't think would work with the radio like it is. regards poppydog

5th May 2018, 9:55 pm	#10
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Concertona Tuning Cap 5.71V certainly isn't too shabby, no -- a radio should work with less. But if the set plays fine on LW with 5.71V from a bench PSU but not from the battery, suspect a weird fault with the battery like one cell going high-impedance to AC. Is there an electrolytic capacitor wired across the battery (perhaps downstream of the on-off switch)? If so, try replacing it -- a bigger value will be fine. It's exactly the job of that capacitor to keep the oscillator going at low frequency, when there is the maximum energy in each cycle. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

5th May 2018, 10:17 pm	#11
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap The 5.71v was not from the bench supply, it was from the batteries under load, the 6v was from the bench supply and the fresh replacement batteries. There was a 500uf trojan cap after the on/off switch which wasn't soldered properly in the very beginning, upon testing it was no good anyway and was replaced with a 470uf regards poppydog

5th May 2018, 11:10 pm	#12
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Concertona Tuning Cap That was my understanding; but I meant, did you also try turning down the bench PSU to find the point at which the set cut out on LW? If the set works from the bench PSU even below 5.71V, then I would suspect a dodgy cell. A faulty cell could conceivably do strange things under a changing load, that will not show up on a simple multimeter test. If there's a 1-10µF original capacitor near the oscillator section, try changing that. This is one of those moments where you really need an oscilloscope ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

5th May 2018, 11:32 pm	#13
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap What I will do is try it on bench supply, winding down voltage until lw stops. I ended up replacing all 3 of the electrolytic caps, the lower capacitance ones were very bad. I will also try some rechargeable batteries just to check, will look tomorrow. The oscilloscope is out of the question im afraid unless I could find one that you could watch Baywatch on regards poppydog

6th May 2018, 8:35 am	#14
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Concertona Tuning Cap Check the transistors voltages, if ok try changing the transistor. Lawrence.

6th May 2018, 10:07 am	#15
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Concertona Tuning Cap Will have another look at voltages. The oscillator transistor has no markings on it so I will have to try to work out what it is, if a replacement is needed. regards poppydog

12th May 2018, 12:15 am	#17
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Concertona Tuning Cap Mine is a smaller model with an all plastic cabinet. Yours looks quite posh by comparison.