Grunow 1291B antenna question - Printable Version

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Grunow 1291B antenna question - murf - 04-13-2023

Hi guy's and gal's.
Have a Grunow Teledial model 1291B That I am having issues with the proper antenna hookup.
This chassis has 2 antenna terminals.
One is for antenna and the other is labeled Doublet.
I assume the doublet is for shortwave?
I know I have to have about 40 ft of single wire attached to the antenna terminal to get rid of motor boating on certain stations.
With no antenna, motor boating.
With 20 ft of single wire, still have some motor boating.
With 50 ft of single wire, no motor boating.
Tried tweeking the alignment with no change.
Anyone out there have one of these models?
If so, what are you using for an antenna?
P.S. this radio is re-capped and working well other than the antenna issue.
murf

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RE: Grunow 1291B antenna question - Radioroslyn - 04-13-2023

Hi Murf,

Touch the grid cap on the 6K7 rf amp and hear if that quenches the motor boating. I suspect it will. Check the ant side of the band switch for cleanliness and good connection. The value of the cathode resistor in the rf amp stage. If too low that can be the issue. Too high it will just work lousy. If you have a spare 6K7 give that a try. See if pin 1 on the socket (6K7) is grounded. It maybe used as a tie point for other things, they don't show on the pictorial.  If there isn't any other connection go ahead and ground it. Align the rf stage w/a generator. As a last resort try adding .047 630v cap from pin 4 (screen grid) to ground.

 https://worldradiohistory.com/Archive-Rider/37/Rider-1937-GHI.pdf
Go to pg 197

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RE: Grunow 1291B antenna question - MrFixr55 - 04-13-2023

Using the schematic on Pg 197 of the 1937 Riders, check resistors 1 and 2 and Cap 50. These are in the AVC circuit and a problem here, especially with the cap or with miswiring could cause motorboating.

Is there motorboating when the selector is in the Phono position? If so, check the audio section. Is there motorboating in all bands or just some? Also check the antenna coils (input to grid of RF) for open secondaries.

Is this the 12B or 12W Chassis? Based on the schematic, the 12B is a really neat radio and should really kick it. The 12W should really really kick it!

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