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 Post subject: Grigsby-Grunow model 90
PostPosted: Apr Tue 07, 2020 11:04 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 311
Location: Isanti MN
Having trouble reading the schematic. Writing is small and very smudged. Especially this part.

Also, I have searched the chassis and can't seem to find the original resistor.

The resistor in question is in series with the first audio transformer. The resistor might have been clipped out. Or something happened early on in this restoration. Need to move past this mystery.

I found a similar A-K radio that used a 30K resistor and another that uses a 54K. Can someone nail this down please?

Also, this resistor ties to the C section of the main PS filter capacitor. Would there be a problem of locating a modern filter capacitor inside the radio chassis, not in the PS? Seems local filtering would be better and eliminate a long wire.

Thanks, TJ


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 Post subject: Re: Grigsby-Grunow model 90
PostPosted: Apr Wed 08, 2020 12:11 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30554
Location: Livermore, CA
Hi

Try "control +" to enlarge the schematic.

http://www.nostalgiaair.org/pagesbymode ... 040017.pdf

Model 90 used a separate power supply.

http://www.nostalgiaair.org/pagesbymode ... 040010.pdf

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Norm


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 Post subject: Re: Grigsby-Grunow model 90
PostPosted: Apr Thu 09, 2020 7:51 pm 
Member

Joined: Oct Thu 13, 2011 8:26 pm
Posts: 311
Location: Isanti MN
Ahhh, thank you, thank you. Helps to have the right schematic that makes sense with the circuit one is finding.

I am working on a model 90. not 90-B.

And the PS schematic too. 80 volt AC input, that is why there is a Ballast in the AC line and why when I powered the transformer it only took about 80 volts input to get 5 volts on the rectifier filament.

Many questions just were answered. Thanks. TJ


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