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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 2nd Jun 2010, 6:51 pm   #1
howard
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Default Grundig 3028 220v - 240v conversion

Hello,

I've at long last converted my German spec Grundig 3028 Hi-Fi Zauberklang to run on 240 volt UK voltage. Moreover I've done it the way that Grundig (UK) converted imported German 220v spec 3028 sets to the 240v 3028 Marlborough versions.

The R & TVS circuit diagram for the 3028 Marlborough suggests that the mains transformer had a 240 volt tapping but a scrap Marlborough in my possession has the same transformer as the German Hi-Fi Zauberklang. What Grundig had done was to disconnect and tie off the 160 volt tapping wire, mount an 82 ohm 10w wirewound resistor on top of the fuse board, and then connect it between the 160 volt and the 220 volt fuse tags.

So I removed the resistor and tag board off the Marlborough fuse board, soldered it onto the top two tags on the Zauberklang fuse board, disconnected the 160v tapping wire from the 160v tag and soldered it onto a spare tag on the tag board, and then soldered the the wires connected to the 82 ohm resistor to the 160v and 220v fuse tags. Finally I stuck a 240v label over the 160v label.

And bingo, it works, indeed the Zauberklang sounds a little sweeter with its valves running at the correct voltages.

One would have thought Grundig would have supplied a transformer suitable for the UK market.

Howard
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Old 4th Jun 2010, 7:59 am   #2
Kevin Hoyland
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Default Re: Grundig 3028 220v - 240v conversion

Hello Howard.

Well done. I enjoyed reading this Thread. I wonder if this would work with the Saba, Telefunken and other German made radios.

Regards Kev.
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Old 4th Jun 2010, 8:17 am   #3
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Default Re: Grundig 3028 220v - 240v conversion

Hello Kev

This general approach should work with other radios but the resistor value and power rating may well need to be different. A set with more valves would require more HT and heater current and would most likely need a dropper resistor with a higher power rating.
Fitting a dropper resistor like this provides an extra source of heat within the set's cabinet, this probably doesn't matter in a large set but would be a problem in a miniature one.

John
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Old 4th Jun 2010, 10:26 am   #4
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Default Re: Grundig 3028 220v - 240v conversion

Quote:
Originally Posted by Kevin Hoyland View Post
Well done. I enjoyed reading this Thread. I wonder if this would work with the Saba, Telefunken and other German made radios.
Hello Kev,

Ron Bryan fitted a couple of wirewound resistors to the recently restored 220v SABA Schwarzwald but in a different part of the circuit as SABAs don't have that type of fuseboard. This mod would certainly work with any of the big Grundig 1950s 220v sets as they all use that fuseboard and possibly other German brand sets do too.

The resistor and tag board are of UK origin so it shouldn't be difficult to obtain them for converting an imported Grundig 220v set.

Howard
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Old 4th Jun 2010, 11:05 am   #5
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Default Re: Grundig 3028 220v - 240v conversion

Nice work, but shouldn't this have been converted to run on 230 volts, now that we are "harmonised" with the rest of Europe?
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Old 4th Jun 2010, 12:41 pm   #6
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Default Re: Grundig 3028 220v - 240v conversion

Yes I suppose in theory, but it depends on the ACTUAL mains voltage where the set will be used, in this case Howard's house!
Our mains is presumably supposed to be 230 volts, but work is nearer 250 and home 239. I set all sets I repair to the 240-250 tap (particularly Mains/battery sets)irrespective to ensure the heaters are slightly under run, and ensure long valve life for the owner.
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Old 4th Jun 2010, 12:49 pm   #7
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Default Re: Grundig 3028 220v - 240v conversion

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Originally Posted by Tom_I View Post
Nice work, but shouldn't this have been converted to run on 230 volts, now that we are "harmonised" with the rest of Europe?
Well the mains voltage here is around 245 volts during the day .... the Zauberklang is running at the correct HT now.

You're right though, the value of the wirewound resistor (or resistors) is dependent on the local mains voltage and needs to be calculated.

Howard

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Old 4th Jun 2010, 1:04 pm   #8
Kevin Hoyland
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Default Re: Grundig 3028 220v - 240v conversion

Hello,

The mains voltage around us in Rotherham is 247 to 250 volts in the day.

Howard the Saba job was effective and neat.

Regards Kev.
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Old 4th Jun 2010, 2:28 pm   #9
Leon Crampin
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Default Re: Grundig 3028 220v - 240v conversion

They sell you quite a bit more electricity by keeping the voltage at the higher limit. Power varies as the square of voltage...

Leon.
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Old 4th Jun 2010, 2:40 pm   #10
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Default Re: Grundig 3028 220v - 240v conversion

The nice way to get 220V from 240V is to use a small transformer with a secondary connected in inverse series with the mains to the radio. To drop 15V you need a 15V secondary etc. Need only be a very small device, the radio power rating divided by the voltage ratio. Hence for a 20V drop and a 50W radio it's 50/(240/20) = 5W. In other words the smallest you can find.

Leon, your comment about selling more electricity is only partially true. Any appliance with a switchmode PSU (PC, TV etc) or a thermostat (iron, fridge, immersion) or a kettle will use the same amount. Lighting and some vintage sets will use more at higher voltages.
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Old 4th Jun 2010, 7:09 pm   #11
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Default Re: Grundig 3028 220v - 240v conversion

I've got three of these, two have the dropper resistor like Howard described above, and one has a transformer with a 240vac tap. All look original, so it may be that Grundig changed the design (not uncommon). When I get a moment, I'll post the serial numbers to see if there was a break-in-point.
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Old 4th Jun 2010, 9:14 pm   #12
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Default Re: Grundig 3028 220v - 240v conversion

Kev,
Take a look at this website
http://www.dms-audio.com/bucking-transformer-diy
or do a Google search for "Bucking transformer"

Mike
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Old 4th Jun 2010, 10:11 pm   #13
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Default Re: Grundig 3028 220v - 240v conversion

Hi. I have some other Grundig valve radios (e.g model 2098) which was made for 220v working. I hope that I can convert this to 240v using this example ?
Mike
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Old 4th Jun 2010, 10:33 pm   #14
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Default Re: Grundig 3028 220v - 240v conversion

Quote:
Originally Posted by swordholder View Post
Take a look at this website
Isn't this exactly what Jeffrey was suggesting in post #10?
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Old 4th Jun 2010, 10:38 pm   #15
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Default Re: Grundig 3028 220v - 240v conversion

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Originally Posted by telstar View Post
Hi. I have some other Grundig valve radios (e.g model 2098) which was made for 220v working. I hope that I can convert this to 240v using this example ?
The 2098 has the same fuseboard and 110, 125, 160 and 220 voltage options as the 3028 Zauberklang, so yes.

Howard
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Old 5th Jun 2010, 1:28 pm   #16
Kevin Hoyland
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Default Re: Grundig 3028 220v - 240v conversion

Hello Mike, outstanding website thank you.

Regards Kev.
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Old 22nd Jan 2013, 1:57 pm   #17
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Default Re: Grundig 3028 220v - 240v conversion

I know it's an old thread now but it has helped me today, thank you .

Having just come back to old valve radios after many years, I have a recently acquired GB (Marlborough) version of the Grundig 3028 which I am just starting out on.

Going over it visually last night, I noticed that the fuse appeared to be in the wrong position, i.e. the 160V tapping. It has the modified German transformer but the original Grundig modified voltage 'stick on' indicator has long gone and the fuse appeared to be in the 160V position which I incorrectly assumed was still the second from highest transformer primary tapping.

At that stage, I hadn't traced how the dropper was used in the modified circuit and thought it was always used whatever the fuse position. This thread clears up that confusion and therefore I now know the radio hasn't previously been over-run prior to my acquisition through an incorrect fuse positioning.

Last edited by PeterB1; 22nd Jan 2013 at 2:24 pm.
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