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Old 5th Oct 2017, 3:19 pm   #21
AC/HL
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Default Re: Grundig Concert Boy 1100

Which component are you interested in?
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Old 5th Oct 2017, 3:31 pm   #22
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Default Re: Grundig Concert Boy 1100

Thanks!
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Old 7th Oct 2017, 4:14 pm   #23
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Default Re: Grundig Concert Boy 1100

Hi Bill, resevoir capacitors. I've just got hold of one for each set. Now I just need to find a day to do the work...
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Old 9th Oct 2017, 2:42 pm   #24
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Default Re: Grundig Concert Boy 1100

Broke out the tools and my old Weller TCP, and set about replacing the resevoir capacitor on the black-case set. Leon's instructions worked perfectly, many thanks.
Result: no effect. Still faint signals and some hum.
Fitted replacement antenna while I had a think. Realised I could put together some D cells if I raided the Maglites, so tried that. Then switched it to battery! Same faint signals without hum. Short rectifier pulling voltage down? All I can think of for the moment. EDIT: mains circuit does appear to be completely isolated when in Battery mode... I'm tempted to disconnect the back of the good set and tag it on, to see if a known good supply fires it up, but I'm also a little leery of ending up with two dead sets...further edit...fault probably on main board somewhere - if PSU id fully isolated on batteries, then substituting the known good PSU won't make any difference either.

I'll get there!

Last edited by DCBassman; 9th Oct 2017 at 3:04 pm.
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Old 9th Oct 2017, 3:09 pm   #25
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Default Re: Grundig Concert Boy 1100

Just use the batteries.

You can eliminate anything pulling down the supply line by measuring the current. Quiescent current should be well under 20mA.

Have you given the wavechange switch contacts a thorough clean?
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Old 9th Oct 2017, 3:45 pm   #26
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Default Re: Grundig Concert Boy 1100

Actually, no. Meant to do that. Out with the Servisol...
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Old 9th Oct 2017, 4:01 pm   #27
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Default Re: Grundig Concert Boy 1100

Instant result. Working well on mains and battery. Thank you Paul!
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Old 9th Oct 2017, 4:16 pm   #28
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Default Re: Grundig Concert Boy 1100

Always the first thing to try.
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Old 9th Oct 2017, 4:20 pm   #29
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Default Re: Grundig Concert Boy 1100

Good result. The switches on these sets have lots of contacts, many wired in series. For example there could be 3 or 4 switches involved in connecting an AM section of the tuning gang to the coil it's trying to tune - so there are lots of possibilities for crackles and bad contacts.

These switches seem to respond well to being used after a dose of Servisol, so it's worth exercising the AM and particularly the SW switches a few times. The "gram" switch also benefits, although it has comparatively few contacts.

If the set sounds good on FM when mains powered, the quiescent current is probably not too far off. If you have limited measuring equipment, I could measure the total supply current on my set (quiescent current recently adjusted) when battery powered on FM at minimum volume, to give you a guide as to whether your set is miles out or not.

Leon.
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Old 9th Oct 2017, 4:38 pm   #30
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Default Re: Grundig Concert Boy 1100

Will actually go over both sets in a more thorough fashion - I'd guess this might be why Woody is not so hot on AM. Certainly worth a go!
In fact, I think the resurrected one sounds the better of the two - really thumping bass, had to turn it down somewhat!
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Old 9th Oct 2017, 7:12 pm   #31
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Default Re: Grundig Concert Boy 1100

Went into the Woody and gave it a spray. Not a great improvement, but some. There's nothing but motorboating on SW, and AM is definitely needing work. The ressurected one is much better across the board, although all the AM bands are badly affected by electrical noise here. Dwellings are such electrically dirty places these days! Fluorescents, switch-mode power supplies, etc etc. Will take it out onto Dartmoor next week (house and dog-sitting) and see how it does in the wild!
Will really need to invest in a good set of new D cells also.
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Old 9th Oct 2017, 10:00 pm   #32
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Default Re: Grundig Concert Boy 1100

Hi, there is a pcb at right angles to the main board with several solder connections joining them. These joints can fail so it's worth while re-flowing them with a small amount of fresh solder. Also the bridge rectifier can give problems so replace this with four suitable diodes. I have two of these and even though the radios worked the sound improved greatly when the rectifier was changed. Mike
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Old 9th Oct 2017, 10:57 pm   #33
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Default Re: Grundig Concert Boy 1100

"..there is a pcb at right angles to the main board with several solder connections joining them."

I've come across problems with this type of connection with adjacent circuit boards - just close physical proximity, and use solder to bridge the gap! Always worth checking the tracks for good continuity. I always used to bridge the gap with scraps of wire soldered to each adjacent track.

Whatever happened to that "old-time" advice - "never rely on solder alone for a connection, make sure there is a sound physical electrical connection first, then "seal" it with solder"?
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Old 10th Oct 2017, 7:48 am   #34
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Default Re: Grundig Concert Boy 1100

Yes, I've been giving the right-angled connections some thought already, particularly for Woody. That may be the source of the 'no AM' fault as the spray didn't miraculously fix it!
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Old 10th Oct 2017, 8:53 am   #35
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Default Re: Grundig Concert Boy 1100

For general information, I've measured the current drawn from the battery terminals of this set when fed from an accurate 9V external power supply. FM was selected and the volume set to minimum.

Using an AVO Model 8, the current draw settles at about 27 mA, there being some change as the output transistors warm up. This set has previously had the quiescent current set accurately according to Grundig's published service sheet (in German).

Leon.

One characteristic of these sets when set to an AM band is high oscillator radiation. A look at the circuit shows that the oscillator output is fed to a coil on the ferrite rod to achieve mixing with the incoming signal. You could exploit this by using your second set (or any other suitable AM set) to detect the oscillator radiation from the set under investigation. The oscillator runs high and the AM IF is 460 kHz, meaning that if you tune your suspect set to a quiet spot at the low frequency end of the MW band, the oscillator will be receivable on a second set towards the high frequency end of the same band. (Tuned frequency + 460 kHz). I tried this test and it works well.
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Old 11th Oct 2017, 9:36 am   #36
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Default Re: Grundig Concert Boy 1100

Quote:
Originally Posted by Radiocruncher View Post
Hi Den. I have one of these sets as well but haven't got around to even powering it up yet as it's a long way down in the restoration pile. I do have a signal generator that will cover the whole radio which you are welcome to come and have a play with as I am not that far away.
Hope you have a read through this thread first, Graham, as long as nothing is obviously broken, Servisol first! Amazing the simple things you forget when you've not done this sort of work for a couple of decades...
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Old 12th Oct 2017, 8:10 pm   #37
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Default Re: Grundig Concert Boy 1100

Now out on western Dartmoor. It's relatively free of electrical noise, and has enabled me to confirm all AM bands as working. Once evening came, there were a few stations on the K1band and quite a few more on K2. Both benefitted from augmentation with a Sony AN-71 long wire. Medium and Long waves were much clearer than in the centre of Tavistock.
I have myself a good set, when all I expected was a scrapper for parts!
Just needs a handle to be complete...
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Old 12th Oct 2017, 10:14 pm   #38
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Default Re: Grundig Concert Boy 1100

If you can trim the RF front end, the AM performance will almost certainly improve. I wonder if the ferrite rod permeability changes with age.

Don't risk getting the set hopelessly out of alignment, but if you feel confident setting it up, preferably with a generator, you will find the AM to be good - better than a contemporary Hacker. Anyway, glad they both now work.

Leon.
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Old 12th Oct 2017, 10:52 pm   #39
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Default Re: Grundig Concert Boy 1100

Grundigs of that era perform pretty well. They weren't cheap when they were new.
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Old 13th Oct 2017, 10:41 am   #40
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Default Re: Grundig Concert Boy 1100

I'm going to leave well alone, I think. It will be mostly used on FM anyway, and its performance there is nothing short of that oft-misused word, awesome!
If I can get near some test equipment in the future, I might be tempted to align them both, but it's likely to be years, if ever, that i have the space to do that.
Next month, I'll be out here on Dartmoor again, and I'll bring out the other one to see if the AM has improved, as I intend to really have a good go at the switching before then, as well as check out the connections between the PCBs. If I'm really lucky, it will also work well.

Quote:
Originally Posted by paulsherwin View Post
Grundigs of that era perform pretty well. They weren't cheap when they were new.
Oh, indeed! You just looked at them and thought, "Ooh, I bet that sounds good!"

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