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I picked up an old Novico shortwave radio at a garage sale. Missing was the wall plug adapter. The battery pack runs at 9v, but I'd like to find an AC wall converter that I can modify that will let me run without batteries. Is there a relatively easy way to determine what kind of voltage/amps are needed without going over the limits? Thanks in advance!

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  • \$\begingroup\$ You stated the voltage. You can measure the current using an ammeter. Whatever you read, double it, and then go look for such a unit. Do be sure to check the polarity of the entry jack used for the wall adapter, too. Assuming it doesn't directly accept AC, and requires DC, the polarity does matter. \$\endgroup\$
    – jonk
    Commented Aug 25, 2017 at 21:50
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    \$\begingroup\$ What does the F stand for and don't say "find" lol \$\endgroup\$
    – Andy aka
    Commented Aug 25, 2017 at 23:00
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    \$\begingroup\$ Is it a 9V battery like the single battery or is it a bunch of AA cells wired to 9V total? You can get a clue from the type of battery it uses. \$\endgroup\$ Commented Aug 25, 2017 at 23:12
  • \$\begingroup\$ @Andyaka when I was at university the lecturer said "fine" was the accepted translation, (the other 4 letter word would not be accepted) \$\endgroup\$ Commented Aug 26, 2017 at 10:10

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Since you know the voltage, you can safely power the radio. Use a 9 V bench supply or something, and measure the current. If this radio has its own speakers or is intended to drive speakers directly, then run it at maximum volume to get close to the likely worst case current.

Then get a 9 V regulated wall wart or power supply that can supply a bit more and round up to the next higher available current. For example, if you measure 421 mA worst case, get at least a 750 mA or 1 A power supply. The difference from 500 mA to 1 A won't cost much extra.

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  • \$\begingroup\$ Hmm switch mode power supply interference and short wave radios might not be a good mix. \$\endgroup\$
    – Andy aka
    Commented Aug 26, 2017 at 13:00

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