Grundig restoration information

ID: 155503
Grundig restoration information 
30.Dec.07 02:29
0

Dave Brown (CDN)
Articles: 2
Count of Thanks: 35
Dave Brown

I am new to  radio restoration . I have 4 Grundig radio's and want to keep looking for these to collect. The sound of these are amazing. I have some understanding that they need some repairs to keep them alive and working for years to come. I have already replaced the electrolytic capacitors on my SO 112 US and need further guidance on replacing whatever it may take to upgrade the rest of it. I have a schematic, thanks to Radiomuseum and I have some knowledge on what it takes to do good workmanship. I am an appliance technician and the only thing in common with appliance's and radio's is the electricity. I have alot to learn and need a little direction. I have at my disposal a gentleman who has been fixing radio's, mainly in the 1910 to 1930's era. Thanks to all     

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 2
Some knowledge and some specifications needed 
30.Dec.07 10:12

Ernst Erb (CH)
Officer
Articles: 5741
Count of Thanks: 9
Ernst Erb

Dear Dave
I hope my eMail has arrived. I moved this thread to "your" model because then it has a chance to be seen by another owner (can be a guest) of such a nice radio and he/she will then be able to know more about this subject.

Thank you that you already told us which knowledge you have. Somebody then can adapt. What is missing: Most essential is what instruments you have and how you manage them.

Recapping could be the topic for this but it is better if you tell us a bit more what sort of performance you are missing on your set or which fault you detect. Please enter the word recapping to our SEARCH and you find something about this in English here. Unfortunately some good articles in German have not been translated - because translations should be done by members - if possible by members who's motherlanguage is English ...

There is a good translation made for the "Cirtcuitry Analysis on a modern radio" and you find the start here. But for a newcomer to radio this might be too much. It is probably preferable that you buy a very cheap pre WW2 radio - for instance an "All american 5" and read first also about the dangers (electrical shock) by repairing if not done the right way. Well, I don't write this one for you but for other readers ;-)

These sets are very simple to understand and easy to repair and one can learn a lot. German post war radios can be quite tricky - as you can learn by the said series of articles.

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 3
North American Grundig Repair Options 
31.Dec.07 18:26

Laurence W. Stewart (USA)
Articles: 30
Count of Thanks: 12
Laurence W. Stewart

Dave:

Like you I am a fan and collector of vintage audio equipment and Grundig Radios.  The Grundigs, especially the consoles, are an order of magnitude more complex than similar radios of the day.  Many techs in North  America won't touch them.  However, I have found one highly regarded tech who will recap and upgrade them.  The price I was recently quoted was $18.00USD per tube plus parts.  I consider that very reasonable.  Unfortunately, he is on the other side of the continent; NY state.  I have also found a local tech in Denver who is a retired radio and tv tech, very skilled in tubes and Grundigs.  The problem is that he is very far behind.  I gave him a poject before Thanksgiving but don't expect to see my unit until March!  His price is $150.00 + parts.  If you want more information, email me.

Regards,

L. W. Stewart

Michael W. Slusser
Director - Operations

Radio Daze, LLC.
p: 585-742-2020 ext. 101
e: mws@radiodaze.com

w:www.radiodaze.com

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 4
Grundig 3028 restoration 
31.Dec.07 19:20

Howard Craven (GB)
Articles: 110
Count of Thanks: 28

 

Hello,

By co-incidence I am about to restore my first Grundig valve (tube) radio, a totally original 3028 Hi-Fi Zauberklang AM/FM set from 1956 which I believe is known in the USA as the 3028 Majestic (for which I see there is no model entry yet). There is a picture of my set on the model page and as can be seen it is in excellent cosmetic condition requiring just a clean and polish to its case and trim. However, it suffers from several faults, typical I am told of Grundig radios of this period, notably its EM34 magic eye is dead, the dial cord slips on all AM wavebands and the four tone controls are not as effective as they should be. It does work but lacks sensitivity and does not sound as good as it should so all its valves will be tested and replaced where necessary and probably all its WIMA brand capacitors and its audio coupling capacitor replaced as well. The dial cord will be fixed and then I will see how this set then performs and if necessary further remedial work will be done.

I will let you know how we get on with this restoration.

Howard Craven.

 PS: Does anyone have a complete service sheet for this radio model please, this is a German spec set so a German one will be fine. Thanks.

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 5
Grundig 3028 restoration 
16.Jan.08 15:13

Howard Craven (GB)
Articles: 110
Count of Thanks: 15

Hello again,

I have now worked out what faults exist in the old Grundig 3028 Hi-Fi Zauberklang, equivalent to the 3028USA Majestic. Some of the lozenge shaped capacitors have been removed and tested and all were found to be leaky so all of those will be replaced. The 4700pf audio coupling capacitor was also leaky and it is absolutely essential to replace this one to avoid damage to the EL84 output valve and the output transformer.  Some other electrolytic capacitors and one smoothing capacitor have already been replaced some 30 years ago and are OK. The dead EM34 magic eye will be replaced and one or two other valves/tubes are worn but all will be tested and replaced as necessary. The AM dial cord has already been repaired once and has broken again so will be replaced but the clutch is working, just. The cord which operates the AM ferrite rod aerial is also slack so that will be repaired/replaced. The internal on/off switch is prone to sticking so it maybe necessary to take that apart and overhaul it. Lastly the rubber  'graphic equalizer' band viewed though the dial above the piano keys which is moved around by the four tone control mechanisms has disintegrated so that will be replaced.

Pic below of some of the leaky capacitors to be replaced.

I should finish restoring this set in two/three weeks time, and I'm looking forward to hearing it working again as it's a very nice radio !  I'll do another write up of the work done on completion.

Regards ........ Howard Craven, Surrey, England

Grundig leaky capacitors

 

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 6
Grundig 3028 Hi-Fi Zauberklang AM/FM 6 valve radio 
11.Feb.08 12:22

Howard Craven (GB)
Articles: 110
Count of Thanks: 8

 

Hello again,

The Grundig 3028 is nearing completion and is now working on all wavebands. The case is complete and here she is now, after just a good clean and polish. I have to say that this is a stunning looking radio and sounds wonderful !  A write up of the internal repairs will follow later this week.

Regards ....... Howard Craven, Surrey, England

 

 http://www.radiomuseum.org/forumdata/users/4885/Grundig_3028_Hi-Fi_Zauberklang.jpg

 

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 7
1956 Grundig 3028 Hi-Fi Zauberklang AM/FM radio restoration 
13.Feb.08 20:44

Howard Craven (GB)
Articles: 110
Count of Thanks: 30


Hello again,

The Grundig 3028 restoration is now complete. Two of us here in Guildford, Surrey, England restore old valve and transistor radios, myself a retired IT Consultant and my colleague Ron Bryan a retired electrical engineer. I do the cosmetic work and some of the simpler electronic work, and Ron diagnoses problems and does the more complex electronic work as he has far more experience than me and has a well equipped workshop.  This was the first Grundig valve radio that either of us have attempted to restore but we encountered much the same problems with this set as with many other UK, German and North American valve radios built in the 1950s. This set is just bigger in size than any others restored to date !  Rather than go into fine detail, I will go through the restoration at a high level and then if anyone has any questions or needs more detail then I will respond to them separately later.

Schematics and Service data

This radio is a German spec Grundig 3028 Hi-Fi Zauberklang and the circuit diagram for it is available from its model page. I also took copies of the documents filed for the Grundig 3028 Musikgerat model and then later I managed to obtain the service data sheet for the Grundig 3028/W/3D Marlborough radio which is a UK spec version of the radio and that contains the realignment procedure in English.

Capacitor / resistor replacement

Radios of this age will almost certainly have a number of leaky or high resistance capacitors and it is a good idea to replace any wax or damaged capacitors before attempting to power up a set to avoid damage to other components. Some work had already been performed on this set probably 30 odd years ago as there was fitted 3 replacement axial capacitors of UK origin but all the rest were original.  A sample of four of the blue and green lozenge shaped capacitors were removed and tested and found to be leaky so all the capacitors of that type were replaced. These were tested later and all were faulty. A number of the small red polystyrene capacitors were checked and they all proved to be fine so they were all left in place. The output valve coupling capacitor was tested and that was leaky so that was replaced. Finally the 10uF crossover network capacitor on top of the output transformer was tested and that was found to be leaky so that was replaced. I also replaced the three old UK replacement capacitors as these are known to fail sometimes.
Several resistors were checked and all were found to be fine so all the original resistors were left in place.

Tuning cords, clutches and rotating ferrite aerial cord

On acquisition only the FM tuning pointer moved, the AM cord was broken. For AM tuning, these sets have two cords connected together, one made from steel wire and the other from cotton cord and it was the steel wire that was broken. It had been repaired before so I decided to replace it all. Unfortunately I was unable to obtain any suitable wire cable so I used modern reproduction cord obtained in the USA. The pulley wheel on the end of the tuning capacitor was broken in half so that was stuck back together with superglue. New cords were made up to the lengths specified in the documentation and fitted.
There was then the opportunity to check the working of the two clutches, the FM clutch was fine but the AM clutch was obviously worn but once engaged it didn't slip so I left it at that. All the pulley wheels and the tuning spindle were each given a drop of oil. The cord to the rotating ferrite rod aerial had stretched over the years but was not rotten so I shortened it slighly and put it back on.

The graphic equalizer display

This is simply a piece of red elastic band, round in section, visible under the dial just above and operated by the four tone wheels. I was unable to find any red elastic so I used white extracted from some knicker elastic and fitted that through the holes. It wouldn't accept red dye or paint so it remains white.

 

Initial listening test

The set was switched on and it was now working quite well on MW, on VHF it was picking up only one or two stations down one end of the waveband, on SW it was working OK but very softly but on LW it was picking up just a couple of MW stations. I replaced the ECC85 valve and that brought FM back to life and that was now working well and sounded very good. The EM34 magic eye was dead so I fitted a secondhand replacement which is a nice bright one but it wasn't closing properly when tuning on AM. And then the set wouldn't switch on. There is an internal on/off toggle switch in these bolted onto the end of the switch assembly and operated by a bar that comes out the side of it. It wasn't working as it was clogged with dust so I cleaned that out and sprayed it with switch cleaner and away it went again.

Fixing LW and Realignment

Ron Bryan investigated the LW problem and found that a wire to the LW loading coil was broken, the top of the coil was damaged and also the core inside it was disintegrating. So the coil assembly was removed from the chassis, its crumbling core was removed, the thread inside retapped and a new core fitted, the coil replaced on the chassis and the wire reconnected - a very tricky job as the wire is very fine (38swg = 0.006") and only a tiny piece remained on the coil to solder onto - and the coil then adjusted OK. This restored LW operation, but LW was still weak compared with MW and the dial calibration was well out, so the 468kHz AM IF was realigned. It was during the IF realignment procedure that an error in the documentation was discovered, the docs incorrectly indicate the position of the first AM IFT which in fact it turned out to be an FM IFT so the FM IF then had to be realigned. MW and LW RF realignment then followed. This improved MW significantly but LW remained around 10% weaker but still perfectly listenable. The voltages to the valves were all checked and they were fine.
Also evident when playing was an occasional high pitched ringing noise at first thought to be AF instability but which I found stopped when pressing on the EL84 valve so I replaced it with a brand new EL84 and that cured that problem.

 

Cosmetic restoration

The case only had one or two tiny marks on it so I simply polished it with Topps medium wood scratch cover. The trim and knobs were brushed clean with upholstery cleaner.  When playing a slight rattling sound was coming from the main loudspeaker - I discovered that the badge was loose and and its loosened tabs were colliding with the loudspeaker the other side of the baffle. So out came the loudspeaker - a tricky job which also entailed the removal of the adjacent side speaker - I removed and polished the brass badge, painted in the white 'Zauberklang' text, revarnished it and then refitted it firmly. The sponge around the inside rim of the loudspeaker was disintegrating so I brushed that off and replaced it with draught excluder and refitted it and the side speaker.

This is a well built radio with wonderful sound quality and good sensitivity and it is in exceptionally good cosmetic condition. It took us around 40 hours in total to restore it but it gave us both a lot of satisfaction to hear it working again.

Regards ........

Howard Craven and Ron Bryan, Surrey, England

 

 

 

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 8
grundig 
14.Feb.08 15:37

Maitiu Standun (IRL)
Articles: 160
Count of Thanks: 15
Maitiu Standun

hello howard, thats an absolutely amazing restoration, pity you dident give us a pic or two [before] as well as [after], and then we would see the amount of work by comparing , full marks to you and ron for bringing this fine radio back to prestine condition , best regards maitiu.

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 9
grundig 
14.Feb.08 20:14

Howard Craven (GB)
Articles: 110
Count of Thanks: 13

Hello Maitu,

I'm glad someone found my article interesting. I didn't take any before pics, I forgot. 

Regards ........ Howard

 

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 10
grundig 
15.Jan.12 05:22
7696 from 28790

Mike Kuhl (USA)
Count of Thanks: 11

Very cool project and very nice job. I just stared work on a Grundig SO141 console that I fell in love with.

There is such a wealth of knowledge on this site, thanks to everyone!

I'm having trouble getting one of the stereo speakers to work and am thinking about replacing it with a new/different speaker set. Since this is my first old radio project, I'm looking to absorb any knowledge possible.

How do I go about selecting a replacement speaker? I tested the speaker and it rates at 3 ohms. 1), is that normal? Should I be looking for a 3 ohm speaker or a 4? Also, what power range should I be looking for?

Thanks for any help you can provide.

 

Mike Kuhl

Lincoln, NE USA

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