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Old 22nd Dec 2015, 12:34 am   #101
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Default Re: Grundig Concert Boy 1100

I have some good news, I have thoroughly cleaned and reassembled and installed a brand new 400ma fuse, given all the switches and sliders a quick squirt. It's now working on mains and battery and it looks and sounds like new and it has been as good as gold all evening. I would like to say thank you for all the help and especially the patience. I have several of these Grundig radios from the 70s and if it is ok in the New Year I may be on here again asking lots more questions on how to do things, if that is ok.
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Old 22nd Dec 2015, 8:23 pm   #102
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Default Re: Grundig Concert Boy 1100

That's fantastic news! Well done for not giving up on the set.

It would be prudent to check that the AC187 and 188 are not getting too hot after an hour or so of continuous operation; but given that the radio seems to have behaved itself so far, they probably won't be. If you can stand to touch it with the outside of your finger (always test anything that might be hot or elecrified with the outside of your finger, so your instinctive grip reflex will pull you away), it's safe.
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Old 22nd Dec 2015, 9:05 pm   #103
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Default Re: Grundig Concert Boy 1100

Thanks for the advice, I will open it up and check tomorrow as it will probably be on for most of the day tomorrow. Once again thanks to everyone for your patience and help.
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Old 23rd Dec 2015, 4:25 pm   #104
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I have been watching this thread with interest and its great to see a positive result at the end of the day!
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Old 23rd Dec 2015, 6:39 pm   #105
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I obtained a good one with a poor cabinet and another vice versa to make up an excellent example. If you exercise care in use it should last well.

Grundig sets of this era show up how mediocre the efforts of most British manufacturers were at the time, eventually leading to them becoming merely badged far eastern imports.
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Old 6th Jan 2016, 8:02 pm   #106
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Default Re: Grundig Concert Boy 1100

Hello, I'm afraid this is no longer a happy ending. I turned the set on after my tea this evening, got a loud hum and now nothing! It is doing exactly the same thing as it was before, a very low voltage reading of 2.8v and the AC187K is red hot again. It's also blown the 400ma fuse. It's a shame as I have had it on nearly every day for 2 or 3 hours a day and it has been fine.
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Old 7th Jan 2016, 10:49 am   #107
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Sorry to hear that and I appreciate this setback might be disheartening. On the positive side, you have a radio that you have now proven will work once the problem has been sorted and the parts that will need replacing are relatively inexpensive so it is probably worthwhile to try again.

I notice from the previous comments that once the power supply was sorted, that most of the attention regarding the audio output stage was been given to the transistors that had obviously failed, which was fair enough. However, since they appear to have failed in the same way again, there is evidently a further fault condition that is leading to their breakdown over a period of time. Depending on where you purchased from, it is possible that one of the ACxx transistors was not up to spec, but since everything worked, at least for a time, I think that an unlikely explanation although perhaps someone else will comment on this.

I would guess that the most likely cause is the output decoupling capacitor, marked C655, 1000uF, 10v, which may be leaking current, shorted or have an intermittent fault. I would be inclined to replace both C654 and C655 with 16v rated parts. Unfortunately, you will also have to check which transistors have failed again and replace those too. Once these have been replaced, I would suggest that you follow the advice to monitor the temperature of the transistors as julie_m suggested.

I would also check the power supply as you did before, by switching to battery and checking the output voltage from the rectifier. I suspect it will probably be OK though. You power is likely being dragged down by the failed transistors as before.

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Old 7th Jan 2016, 11:47 pm   #108
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Default Re: Grundig Concert Boy 1100

Thank you for the kind comment, unfortunately yes it is very frustrating. I will get around to looking at this again in the next few days. I need to try to find components suppliers that are cheap and reliable (if there is such a thing). I seem to be paying a lot for parts and even more for the postage and then having to wait for a week for the parts to arrive! If anyone can point in the right direction for a good components supplier I would be much obliged. On the plus side I have recently purchased a AVO Multiminor 5 so at least I will have a chance to use that.
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Old 8th Jan 2016, 10:57 am   #109
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Default Re: Grundig Concert Boy 1100

CPC send all components ordered on line free of carriage charges to [B account holders[/B]

So, if you buy components on a regular basis, it may well be worth your while opening an account with them. Delivery of in-stock items is usually next working day, sometimes 2 working days later. (Usual disclaimer - I have no connection with CPC, other than having been a customer and account holder for many years now)
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Old 8th Jan 2016, 11:22 am   #110
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In the past I have used Farnell for larger orders over £20 otherwise there is a steep postage charge, although delivery is usually next day. Unfortunately, they do not appear to list the AC187(K) or AC188(K). I have also sometimes used Bitsbox for some basic parts but again, they do not stock the above transistors. Occasionally I have been able to get a part for a reasonable price from my local Maplin, although generally, they seem to be rather overpriced and their inventory appears to be quite limited. Some on here have recommended Cricklewood Electronics. I haven't used them myself yet, but they do list the AC187K and AC188K as well as the capacitors you might need so may be worth a try.

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Old 8th Jan 2016, 12:29 pm   #111
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Default Re: Grundig Concert Boy 1100

Incidentally, with the AC187K and the AC188K although buying the 'K' variant saves you a bit of time, you can save a couple of quid if you buy the non 'K' variant. The transistor itself is the same except for the square heat sink attached. It is easy enough to extract and replace the transistor by very carefully using an appropriate screwdriver on the slotted side of the block. The two halves should not be forced apart, but just opened ever so slightly to provide enough slack to release the transistor but not deform the block. Make a note of the orientation so you can put the new one back using the exact same orientation. This will usually just push back in. The action of clamping it to the larger heatsink in the radio will tighten it back up again.
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Old 2nd Feb 2016, 12:06 am   #112
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Default Re: Grundig Concert Boy 1100

Wavey Dipole - thanks for the tip about buying the non 'K' variant. I bought a handful of them from Germany far cheaper, even with the postage, than what they would have been over here. I have pulled the radio to pieces and will be doing some testing tomorrow night.
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Old 2nd Feb 2016, 11:41 pm   #113
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Default Re: Grundig Concert Boy 1100

Tested the rectifier this evening, according to the meter everything is ok, unsoldered capacitors C805, C654 and C655 - tested them with the meter and seem ok. I put 9v into each one and it seems to have took that ok. I unsoldered AC187, AC188 and AC121 and they all tested ok even though AC187 was red hot. This is not good as I was hoping to find something somewhere that was not good. I don't want to replace parts that don't need replacing, however could there be intermittent faults. As I said before when I turned it on it made a really loud hum, as if there was a huge surge.
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Old 4th Feb 2016, 8:19 pm   #114
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Default Re: Grundig Concert Boy 1100

Can anyone please point me in the right direction where to get one of these? It is a 16v 2200uf cap. I'm having trouble locating one. Thanks
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Old 4th Feb 2016, 10:15 pm   #115
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Default Re: Grundig Concert Boy 1100

2200 μF is a common enough value. A higher voltage capacitor can safely be used as a replacement. If it is in the power supply (which is always the largest value capacitor in a transistor radio), even a higher capacitance value will be fine. (But it it's between the amplifier and speaker -- the other high-value capacitor in a transistor radio -- do not exceed half the value of the power supply capacitor; otherwise, you probably will get nothing but a "farting" noise from your radio.)

The new capacitor will only have a positive and a negative lead, so you might have to be a bit creative when installing it -- the soldering points that went to the can (negative connection) probably will need to be joined together, if the can itself was used to complete the circuit.
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Old 4th Feb 2016, 10:25 pm   #116
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Default Re: Grundig Concert Boy 1100

Thank you for the reply, that's about the only thing I am good at is being creative with the soldering iron!

Another quick question - I have one of these cheap Chinese ESR meters, and I have been testing the original caps off the radio and nearly all of the values of them seem to be a little bit higher than is stated on them, and the replacement capacitors (new modern ones) that I have, the values are a little lower than stated. Is this the norm, or are my original caps suspect i.e. high resistance and my new caps lower resistance than stated cheap and nasty ones? Thank you
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Old 5th Feb 2016, 12:26 am   #117
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Default Re: Grundig Concert Boy 1100

It is normal for capacitance to vary to a certain extent from the stated value due to tollerance. For generally available electrolytic capacitors the tolerance is usually +/-20% although for some applications, capacitors with closer tollerances might be used. This means that the reading could vary by up to 20% from the stated value in either direction. If they vary 'a little' enough to remain well within tolerance then they might by Ok. If they are beyond -tolerance then they they clearly are not. Having said that, given their age, that replacements are relatively cheap and since you have evidently removed them for testing, you might as well replace with new ones.

If by resistance you mean ESR, then one should expect it to be lower since modern capacitors are smaller than their older equivalents. It follows that the dielectric is thinner which means lower ESR and is nt necessarily a bad thing.

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Old 5th Feb 2016, 4:34 am   #118
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An ideal capacitor has no equivalent series resistance; but in real life, the plates, leadout wires and electrolyte are not perfect conductors (although modern production processes have helped reduce ESR even since 50 or so years ago). The ESR of a capacitor will be lower when it is brand new, and will eventually increase as electrolyte is gradually lost by decomposition or evaporation. Electrolyte loss happens faster at higher temperatures.

ESR (unless it is outrageously high enough to render the capacitor useless) is usually only critical in a few specialist applications such as switched-mode power supplies, where there are brief, heavy current pulses. If ever a capacitor absolutely needs to be of a low-ESR type, it will be marked as such on a circuit diagram.

In most circuits, at the frequencies involved, the capacitive reactance will dominate and the ESR can be neglected.
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Old 12th Feb 2016, 2:01 pm   #119
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Default Re: Grundig Concert Boy 1100

Another quick question - I have some AC187/01 transistors, can I use these in place of my AC187K on my Concert Boy 1100? I've had a quick look at the All Transistors Datasheet and there are some differences but I would like to ask on here just to be safe. Thanks
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Old 12th Feb 2016, 2:18 pm   #120
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Default Re: Grundig Concert Boy 1100

AC187/01 is the same. In my earlier post, I mentioned the R650 preset that you said
was a bit touchy when setting up the current, so it might be worthwhile replacing this.
(use 50 or 47 ohm type)
You can set it for an even lower current, but the penalty will be audio distortion at low volume, worsening as the battery voltage falls, no problem if you intend to use it on the mains.
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