Grundig 30/28/W/3D - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Radio_Dave · 6th May 2009, 5:30 pm

Hi Kev,

IIRC the 0.3 amp fuse that you swapped for a bulb is used for input voltage selection? If so are you positive that it was in the right position?

Regards
David

Tim · 6th May 2009, 6:50 pm

Sounds as though transformer is Ok. Run the set with rectifier disconnected and feel the transformer. I reckon the short is on the HT some where.

Station X · 6th May 2009, 6:58 pm

I'm not familiar with this particular set, but the last smoking mains transformer fault I had was down to a faulty bridge rectifier. Try reconnecting the rectifier to the transformer and disconnecting the output of the rectifier from the smoothing capacitors. If the bulb is then bright there's your fault.

Kevin Hoyland · 6th May 2009, 6:59 pm

Hello David.

The 0.3 amp fuse is in the 240v position and i put the bulb inthe same place. I have had the bulb on for 15 mins and the transformer is not geting hot. Thanks for your suggestion and help.

Regards Kev.

Kevin Hoyland · 6th May 2009, 7:50 pm

Hello Graham.

I have reconnected the transformer and taken the output feed to the 2x50 UF capacitor off the rectifier and put the power back on and the bulb is bright. Thanks for your help.
Regards Kev.

georgesgiralt · 6th May 2009, 7:58 pm

So the culprit seems to be the smoothers.
Jan at ask Jan First stock original selenium rectifier and smoothing caps in aluminium cans for the vintage radio sets. Never done business with, but followed a like given by a fellow member and found the site exciting...
Otherwise you can replace the stuff in the rectifier with 4 1N4007 diodes with four 1nF caps in parallel and a current limiting resistor (100 Ohm 25 W are good because they can be bolted to the chassis.) Re-stuffing the capacitors is a more messy job and more difficult because they often are double or triple in one can into Grundig sets.

Kevin Hoyland · 6th May 2009, 8:36 pm

Hello Georgesgiralt

Thank you for your suggestions and help.
Regards kev.

Station X · 6th May 2009, 9:13 pm

Quote:

Hello Graham.

I have reconnected the transformer and taken the output feed to the 2x50 UF capacitor off the rectifier and put the power back on and the bulb is bright. Thanks for your help.
Regards Kev.

If you're saying that the bridge rectifier is connected to the transformer and that the bridge rectifier IS NOT connected to the smoothers, then it's the bridge rectifier that's at fault.

Of course that's not to say that the smoothers are good, but you can check that once you've changed the rectifier.

Kevin Hoyland · 6th May 2009, 9:34 pm

Thanks Graham.

Kev.

Tim · 6th May 2009, 11:16 pm

Sounds like the rectifier. Disconnect everything from it and check.

Kevin Hoyland · 7th May 2009, 6:42 pm

Hello i have taken the selenium rectifier out and taken the top off . The plates inside were burned together please see the photo and the wires were burned to the plates. PS the smell

?

Kev.

Tim · 7th May 2009, 8:20 pm

Well done!! Get the tricky ones out of the way first.
You got to the bottom of it. I see you may be planning to rebuild the innards. A bridge rectifier will do if it's easier(at least 400 volt) and a 150-250 ohm limiting resistor in series with the DC to the set.
Yes the smell of a Selenium rectifier is-er somewhat distinctive, and part of the initiation!
Dont forget to check for shorts on the HT "into" the set just in case.........it would be a shame to have to do it all over again!
Good luck!!

kalee20 · 7th May 2009, 8:48 pm

I'd definitely use the silicon diodes, 1N4007 wired as a bridge, with a 1nF 'Y' rated capacitor across the transformer-input to the bridge. And, a suitable series resistor - as Tim suggests, the value will almost crtainly be within the range 150 - 250 ohms. But, when you get up and running, measure the HT voltage and tweak the value of resistor until it's right. Then, fit a permanent resistor of the nearest standard value, 6W rating.

You can then encapsulate the lot in the original rectifier case.

One thought - if the rectifier has been short-circuit, it might have put AC on the reservoir capacitor and given it a hard time. So, I'd remove all the valves and power up with a significantly higher value of limiting resistor (10k), so that the HT capacitors charge very slowly with no HT drain. If they survive this, and charge to at least 200V, they've effectively reformed. When you switch off, hopefully the voltage will stay high (maybe falling slowly if there's a resistive current bleed). Let the voltage fall to near zero, or discharge with another 10k resistor, before putting your hands in!

Kevin Hoyland · 2nd Aug 2009, 6:32 pm

Hello to everyone hope you are all OK.

After being in and out of Hospital for a long time i have finaly repaired the radio . Replacing the selenium rectiffier and the 2x50 UF reservoir capacitor / 1.3K 4w resistor and the power Transformer.The 3028 is now working like new. Thank you all for your help.

Regards Kev.

JimMac53 · 4th Aug 2009, 3:02 pm

Way to go Kevin!

6th May 2009, 5:30 pm	#21
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	Re: Grundig 30/28/W/3D Hi Kev, IIRC the 0.3 amp fuse that you swapped for a bulb is used for input voltage selection? If so are you positive that it was in the right position? Regards David

6th May 2009, 6:50 pm	#22
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Grundig 30/28/W/3D Sounds as though transformer is Ok. Run the set with rectifier disconnected and feel the transformer. I reckon the short is on the HT some where. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

6th May 2009, 6:58 pm	#23
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Grundig 30/28/W/3D I'm not familiar with this particular set, but the last smoking mains transformer fault I had was down to a faulty bridge rectifier. Try reconnecting the rectifier to the transformer and disconnecting the output of the rectifier from the smoothing capacitors. If the bulb is then bright there's your fault. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

6th May 2009, 6:59 pm	#24
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Hello David. The 0.3 amp fuse is in the 240v position and i put the bulb inthe same place. I have had the bulb on for 15 mins and the transformer is not geting hot. Thanks for your suggestion and help. Regards Kev.

6th May 2009, 7:50 pm	#25
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Hello Graham. I have reconnected the transformer and taken the output feed to the 2x50 UF capacitor off the rectifier and put the power back on and the bulb is bright. Thanks for your help. Regards Kev.

6th May 2009, 7:58 pm	#26
georgesgiralt Hexode Join Date: Jul 2008 Location: Toulouse, France Posts: 406	Re: Grundig 30/28/W/3D So the culprit seems to be the smoothers. Jan at ask Jan First stock original selenium rectifier and smoothing caps in aluminium cans for the vintage radio sets. Never done business with, but followed a like given by a fellow member and found the site exciting... Otherwise you can replace the stuff in the rectifier with 4 1N4007 diodes with four 1nF caps in parallel and a current limiting resistor (100 Ohm 25 W are good because they can be bolted to the chassis.) Re-stuffing the capacitors is a more messy job and more difficult because they often are double or triple in one can into Grundig sets.

6th May 2009, 8:36 pm	#27
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Hello Georgesgiralt Thank you for your suggestions and help. Regards kev.

6th May 2009, 9:34 pm	#29
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Thanks Graham. Kev.

6th May 2009, 11:16 pm	#30
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Grundig 30/28/W/3D Sounds like the rectifier. Disconnect everything from it and check. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

7th May 2009, 6:42 pm	#31
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Hello i have taken the selenium rectifier out and taken the top off . The plates inside were burned together please see the photo and the wires were burned to the plates. PS the smell? Kev. Attached Thumbnails Last edited by Brian R Pateman; 7th May 2009 at 9:43 pm. Reason: Ridiculously large embedded image thumbnailed.

7th May 2009, 8:20 pm	#32
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Grundig 30/28/W/3D Well done!! Get the tricky ones out of the way first. You got to the bottom of it. I see you may be planning to rebuild the innards. A bridge rectifier will do if it's easier(at least 400 volt) and a 150-250 ohm limiting resistor in series with the DC to the set. Yes the smell of a Selenium rectifier is-er somewhat distinctive, and part of the initiation! Dont forget to check for shorts on the HT "into" the set just in case.........it would be a shame to have to do it all over again! Good luck!! __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

7th May 2009, 8:48 pm	#33
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Grundig 30/28/W/3D I'd definitely use the silicon diodes, 1N4007 wired as a bridge, with a 1nF 'Y' rated capacitor across the transformer-input to the bridge. And, a suitable series resistor - as Tim suggests, the value will almost crtainly be within the range 150 - 250 ohms. But, when you get up and running, measure the HT voltage and tweak the value of resistor until it's right. Then, fit a permanent resistor of the nearest standard value, 6W rating. You can then encapsulate the lot in the original rectifier case. One thought - if the rectifier has been short-circuit, it might have put AC on the reservoir capacitor and given it a hard time. So, I'd remove all the valves and power up with a significantly higher value of limiting resistor (10k), so that the HT capacitors charge very slowly with no HT drain. If they survive this, and charge to at least 200V, they've effectively reformed. When you switch off, hopefully the voltage will stay high (maybe falling slowly if there's a resistive current bleed). Let the voltage fall to near zero, or discharge with another 10k resistor, before putting your hands in!

2nd Aug 2009, 6:32 pm	#34
Kevin Hoyland Heptode Join Date: Feb 2009 Location: Rotherham, South Yorkshire, UK. Posts: 559	Re: Grundig 30/28/W/3D Hello to everyone hope you are all OK. After being in and out of Hospital for a long time i have finaly repaired the radio . Replacing the selenium rectiffier and the 2x50 UF reservoir capacitor / 1.3K 4w resistor and the power Transformer.The 3028 is now working like new. Thank you all for your help. Regards Kev.

4th Aug 2009, 3:02 pm	#35
JimMac53 Hexode Join Date: Apr 2009 Location: Naples, Florida, USA Posts: 255	Re: Grundig 30/28/W/3D Way to go Kevin! __________________ Jim Mac