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 Post subject: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Thu 25, 2018 8:33 pm 
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Joined: Jan Wed 17, 2018 7:30 pm
Posts: 40
Hello,
I'm new to this forum, I wish I would have known about this a long time ago.

I was inspired by addyboy's post viewtopic.php?f=6&t=326325 I have a similar issue but have some confusion with the Cap values.

I've had this system for a very long time it never worked but I kept it as a piece of furniture. It's in really nice shape and I've taken care of it. The back panel was lost sometime ago(don't ask) so I don't know what version of the SO191 it is.

I have some experience with electronic repair and using associated test equipment.

I started the restoration and discovered a blown rectifier, some open resistors, caps way out of range etc. The amp is switched for 110v. I want to perform a full recap but have found conflicting information between the schematic and what's actually in the amp. There's evidence of prior repairs but the capacitors in question all look like they are from that era.

Here's my question:
With exception to the X2 electrolytic can type capacitors all my caps are 50uf with relatively low voltages. The schematic shows a combination of both 100uf and 50uf with low voltages. My paper capacitors are all .022uf, my schematic shows 22nf(.022uf) and 2.2nf(.0022uf). I also have 2 tiny 1800p capacitors that don't appear to be part of the schematic.

Not sure what to do.

I greatly appreciate any guidance or advice.

Thanks,
Hector


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Thu 25, 2018 10:02 pm 
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Location: Near Brandon, Iowa
HectorOrnelas wrote:

Here's my question:
(snip...) With exception to the X2 electrolytic can type capacitors all my caps are 50uf with relatively low voltages. The schematic shows a combination of both 100uf and 50uf with low voltages. My paper capacitors are all .022uf, my schematic shows 22nf(.022uf) and 2.2nf(.0022uf). I also have 2 tiny 1800p capacitors that don't appear to be part of the schematic. (...snip)


If your documentation is factory Grundig, I'd be inclined to believe it... assuming of course that it is the correct documentation for your specific model.

If the documentation that you are using is from a Sams folder, be skeptical of its accuracy. I like some features of the Sams product but they are far from being 100% accurate in most cases.

Original paper/foil caps lower than 0.1 uf in most German radios were usually marked in terms of nanofarads (nF). If they are marked in microfarads, chances are good that they have been replaced since the chassis left the factory. Of course, cap brand markings are a good clue as well.


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Thu 25, 2018 10:32 pm 
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Joined: Jan Wed 17, 2018 7:30 pm
Posts: 40
The schematics are Grundig and list 2 different values in nf for the paper caps. The paper caps in the amp are all marked .022uf, they look original or at least very old. See attached.


Attachments:
grundig so191.jpg
grundig so191.jpg [ 116.02 KiB | Viewed 929 times ]
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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Thu 25, 2018 10:37 pm 
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Joined: Jan Wed 17, 2018 7:30 pm
Posts: 40
Sorry, wrong picture of amp. That was addyboys. this is mine.


Attachments:
My amp bottom.jpg
My amp bottom.jpg [ 172.18 KiB | Viewed 929 times ]
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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Fri 26, 2018 7:36 pm 
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http://antiqueradios.com/forums/viewtop ... 1#p2804881

After deviating to Steve's thread above, I'd recommend you go back and start from step one: safety check with a dim bulb tester. This is to make sure the transformer is not shorted.

One lesson I learned from my Grundig. Don't go do full recap all at once. For the first round, just the electrolytic capacitors and paper ones. Go slow, one at a time.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Sat 27, 2018 12:27 am 
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Joined: Jan Wed 17, 2018 7:30 pm
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Thank you. I will proceed with caution.

Here's what I've done to this point.

1 Made a dim bulb tester
2 Transformer was still in working order
3 Disconnected rectifier and it stopped blowing fuses
4 Tested the rectifier, found to be defective
5 Tested all the caps, some were out of tolerance but not shorted or registered as defected
6 Discovered open resisters
7 Tested all the resistors
8 Just found the correct schematic this morning, I now have the correct information for my model

Next Steps:
1 Replace the obvious defective parts.
2 See if amp continues to blow fuses, if successful, move onto step 3
3 Replace caps one and a time, testing the amp in between changes
4 Clean all the sockets and tube pins
5 Review and refresh solder joints in necessary
6 Test voltages

Should I be doing anything else with this amp? I would like to give it the royal treatment while I'm at it.

I really appreciate the information and help I've been given.


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Tue 30, 2018 10:34 pm 
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So I replaced the rectifier, the open resistors, and the 2, 1.8nf caps with 2.2nf caps I had on hand(one of these had a broken lead and the other was bad) The remaining caps and resistors tested ok for now. There is still a short (thank you glow bulb).

I disconnected the circuit down stream of the rectifier and powered it up. The vacuum tubes glow and the fuse does not blow. I'm only registering about 230V at the rectifier and transformer. My schematic shows it should measure 312V.

Thoughts?


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 7:28 am 
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Change out the electrolytic capacitors. A bad filter capacitor in the power supply section could cause damage. Some experienced technicians would even recommend folks not to power up the set until new ones are installed. Don't bother to find which one is bad, change them all.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 2:00 pm 
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AJJ wrote:
Change out the electrolytic capacitors. A bad filter capacitor in the power supply section could cause damage. Some experienced technicians would even recommend folks not to power up the set until new ones are installed. Don't bother to find which one is bad, change them all.

+1
Replace all electrolytics before applying power**

I normally take it a step farther, and replace all suspect components...eg paper/wax caps, out of tolerance resistors, Selenium rectifiers, etc. Many do not agree with this approach......


**
There are a few exceptions...eg some high-end test equipment. My Tektronix scope from the 70s has had a variety of issues, but it still has the original filter caps.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 5:17 pm 
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Thanks. I have all the parts on hand, will get this done shortly and update.

Thanks again.


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 7:39 pm 
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Joined: Jan Wed 17, 2018 7:30 pm
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Just wanted to point out a couple of things about my particular amp. As mentioned, I found my actual schematic tucked in the cabinet. It has differed from all the others I have seen in two ways that I've noted so far. The cap values are different and I do not have a 110/220 selector.


Last edited by HectorOrnelas on Jan Wed 31, 2018 8:20 pm, edited 1 time in total.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 7:53 pm 
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That is not readable. If anyone needs the schematic, it is available at radiomuseum.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Jan Wed 31, 2018 8:34 pm 
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Deleted picture. No sense in posting something that is unusable.

Not able to make it small enough with detail.


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Thu 01, 2018 3:40 am 
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HectorOrnelas wrote:
Just wanted to point out a couple of things about my particular amp. As mentioned, I found my actual schematic tucked in the cabinet. It has differed from all the others I have seen in two ways that I've noted so far. The cap values are different and I do not have a 110/220 selector.


Grundig sets tend to have multiple variations. Use only the one that's correct for your set.

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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 3:25 am 
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I just bought a Sams Photofact for the SO191 (been looking for a while) no guarantee that its specific to yours, but I will post it when I get it........

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Sometimes discussing the wrong path leads you down the right one.....


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 3:30 am 
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I am also picking up tomorrow morning another SO191 for parts.......specifically for the NF2 amp.......intrigued to see what it's cap layout is.

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Cheers, Steve

Sometimes discussing the wrong path leads you down the right one.....


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 10:08 am 
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Joined: Jan Wed 17, 2018 7:30 pm
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I'm missing the back panel on my so191. Would you be willing to sell me the one off your parts doner?

Looking forward to seeing more info on the 191


Thanks ,
Hector


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 7:37 pm 
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HectorOrnelas wrote:
I'm missing the back panel on my so191. Would you be willing to sell me the one off your parts doner?
Looking forward to seeing more info on the 191
Thanks ,
Hector


Hi Hector,
here is the panel you need. Contact the UPS Store on Platt in West Hills, CA 91307 so they can wrap it and ship it to you.......as for me, make a donation to this forum.


Attachments:
IMG_2561.jpg
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Cheers, Steve

Sometimes discussing the wrong path leads you down the right one.....
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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 11:14 pm 
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Wow Steve! That's so generous an cool of you. I hope I can return the favor. I will certainly make a donation to this forum.

I contacted Leslie, the store owner and started to make arrangements. I assume you still have to drop it off. She does not have it in her store.

Thanks again, really appreciate it.

Hector


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 Post subject: Re: Need help with Amp restoration on my Grundig SO191
PostPosted: Feb Sat 03, 2018 11:20 pm 
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HectorOrnelas wrote:
Wow Steve! That's so generous an cool of you. I hope I can return the favor. I will certainly make a donation to this forum.

I contacted Leslie, the store owner and started to make arrangements. I assume you still have to drop it off. She does not have it in her store.

Thanks again, really appreciate it.

Hector


I will drop it off today or Monday......... 8)

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Sometimes discussing the wrong path leads you down the right one.....


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