Grundig 800 Power Adapter

I have a Grundig 800 shortwave radio and need an AC adapter.

Tom Stiles

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Description

I have a Grundig 800 shortwave radio and need an AC adapter. The one that came with it which is not the original produces a lot of ripple making the radio unusable. I have purchased a replacement power supply and it was no better. The original power supplies are not available any more. I tested the radio on a laboratory power supply and the radio works fine however this supply is large and needed for other things. I have purchased a down converter board. I plan to use a laptop power supply which puts out 19 VDC and this converter board to reduce the output to 9 VDC which is needed by the radio. I have numerous laptop power supplies so this is free and the down converter is only a few dollars. It this works out then many people can use this idea to power other things including charging cellphones. The quest is to find out if this concept will provide clean power.

Details

Initial testing of this down-converter looks good except for some high frequency switching ripple it is less than 0.05 volts so it may not be a problem. Here is a video of my initial testing.

Discussions

Tom Stiles wrote 07/13/2016 at 20:34

After setting up this circuit, the initial testing showed that the radio was working fine. However, after listening to shortwave for just 5 minutes interference was heard on all bands. Using my rather simple oscilloscope I discovered what I had feared. This is a switching regulator and the higher frequency of the switching circuit was getting into the radio. Adding inductors on power to the radio did not help. Back to a more basic circuit. Note the radio works fine on a laboratory power supply.

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Jeremiah Johnson wrote 12/29/2016 at 04:41

7809 (9V linear regulator) 3-pin ICs exist. Use the switching supply to output 10.5V or so, and then regulate linearly down to 9V.

Alternately, or maybe in addition to that, adding a cap of the appropriate size on the output of the switching regulator should eat most/all of that ripple.

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