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 Post subject: Grunow 450 osc coil
PostPosted: Nov Sat 04, 2017 12:18 pm 
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Joined: Nov Sat 24, 2012 5:05 am
Posts: 90
I have a Grunow 450 radio with a BC and SW band. The oscillator coil has at least on broken wire. The coil looks like it has a single wrap covering approx 3/4 of the tube form and a second wrap about 1/2 way up the tube with an insulator beneath it. The second wrap is maybe 1/8 of an inch wide and has multiple wraps and it looks like two center taps coming out of the winding also. I can find no ohmage or henry values for this coil anywhere on the Riders Schematic. Can anyone steer me to these values or to someone that can rewind this coil? Thanks

Charles


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sat 04, 2017 3:16 pm 
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Location: Annapolis, MD
Can you post a picture?

I can probably repair it....sending you a PM.

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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sat 04, 2017 7:17 pm 
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Joined: Nov Sat 24, 2012 5:05 am
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Mark,

I have 3 photos of my oscillator coil. But to attach them the site says they are over 256kb. Do you have an email address or know how to make the photos smaller in order to attach them. If it helps my email is hilan56@yahoo.com. There are six lugs and a wire that I believe is a center tap. I have the coil mapped and know where each terminal goes in the radio, if this helps. Let me know if it is something you can tackle. I believe the wire is 36AWG (.005 inches in diameter). Thanks.

Charles


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 1:39 am 
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Location: Annapolis, MD
Here are the OP's pictures
Attachment:
grun_450-3.jpg
grun_450-3.jpg [ 36.88 KiB | Viewed 341 times ]

Attachment:
grun_450-2.jpg
grun_450-2.jpg [ 35.9 KiB | Viewed 341 times ]

Attachment:
grun_450-1.jpg
grun_450-1.jpg [ 38.51 KiB | Viewed 341 times ]


My concern is that the coil looks damaged / altered. But--it also appears that careful inspection might reveal where the break is.

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-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 1:51 am 
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Here is a snip from the oscillator section. (the set has 2 bands, and I assume the BC coil is the one on the left)
Attachment:
osc.jpg
osc.jpg [ 31.32 KiB | Viewed 340 times ]

Which coil are we dealing with?

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 2:14 am 
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and the oscillator ckt from Riders 5:
Attachment:
osc_riders-5.jpg
osc_riders-5.jpg [ 28.94 KiB | Viewed 337 times ]

easier to understand?......;)
It appears that the oscillator coil includes all the windings shown---heaven help us....

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 2:16 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: S. Dartmouth MA 02748-1225 USA
I re-wound a Grunow coil many years ago. Not exactly this model. This coil appears to have been tweaked for inductance at both ends. This will effect tracking if it is wound without the wire pulled away. Or the rewind can be done with two less turns. Or the all turns made but the oscillator coil will have to be tweaked at the low end of the band during re-alignment...

The coil is corroded because of the same reason Philcos failed. The use of celluloid insulating layer, decomposes into an acid...

BTW my rewind was a drop in fit, worked without alignment. I had the correct wire size...

Note: The Grunow I worked on had a couple of bad micas in the oscillator circuits. One was off, bad tracking and one was noisy, like SMD... So, be aware...

GL


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 2:48 am 
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Location: Annapolis, MD
I think this is how things are connected for BC and SW. Note that the tapped coil in the cathode circuit is not tuned.
Attachment:
osc_riders-5__BC.jpg
osc_riders-5__BC.jpg [ 33.44 KiB | Viewed 333 times ]

Attachment:
osc_riders-5__SW.jpg
osc_riders-5__SW.jpg [ 33.34 KiB | Viewed 333 times ]

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Nov Sun 05, 2017 3:30 am 
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Joined: Nov Sat 24, 2012 5:05 am
Posts: 90
I am using the more conventional schematic from Riders GRUNOW PAGE 7-1. Near as I can tell based on how the oscillator was wired into the radio, I have continuity on the middle coil the one that has the 3000pf cap at the bottom and continuity on the right coil between the center tap and the bottom of the coil. I cannot seem to get any continuity on the left coil or top of the right coil. I have wound antenna coils, but this has me concerned that I maybe starting something that is beyond my abilities.


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 Post subject: Re: Grunow 450 osc coil
PostPosted: Dec Fri 01, 2017 5:19 pm 
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Joined: Nov Sat 24, 2012 5:05 am
Posts: 90
Finally some progress. I so appreciate everyone's input. Attached are two pics of the coil I rewound. I also had a cracked phenolic tube socket for my 42 output tube. Got that changed and the radio came alive on one station only. So I aligned it and got more stations. However the dial is off of the stations that come in. It is probably cuz I did not get the turn count on the oscillator coil exactly correct. I have the oscillator trimmer screwed all the way in and with tuning cap fully closed which should be 540KC (since the schematic states the radio range is 540KC to 1500KC). I currently I receive 830 at 700 on the dial, 1020 at 900, 1130 at 1000, 1280 at 1190 and 1500 at 1450. With the oscillator trimmer screwed fully down, I was thinking of adding a 50PF cap from the trimmer to the oscillator coil to let me unscrew the oscillator trimmer some and give me some additional capacitance to try and get a better dial to station tracking. Or I could just leave it alone. Any input on this would be appreciated. I maybe over thinking or engineering this.

Charles


Attachments:
IMG_1580.jpg
IMG_1580.jpg [ 47.87 KiB | Viewed 157 times ]
IMG_1581.jpg
IMG_1581.jpg [ 44.17 KiB | Viewed 157 times ]
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