Cobra 18WXSTII IRF520 MOSFET Mod.

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fsjonsey
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First Name: Bryan
Location: Cleveland OH, USA

Cobra 18WXSTII IRF520 MOSFET Mod.

Post by fsjonsey »

I was able to successfully install an IRF520 MoSFET final in a Cobra 18WXSTII+. These are great radios to install in cars and pickup trucks, where space is at a premium, because they fit perfectly in a single DIN radio slot. A modified 18WXST will Dead key at around 10 watts, swinging to 30.
Parts needed:
One IRF520 MosFET
One EKL EN-1230 Companion Part, either the official version or a Home made equivalent.
Silicone heat sink grease.

Remove R110, R83, The Slug from coil L17, and Q25, the 2SC2078 final.

Install the EKL EN-1230 companion part at R110, with the positive leg facing the rear of the radio.
Install the IRF520 Mosfet at Q25. Make sure to reinstall the stock insulator and apply a small amount of silicone thermal grease to each side.
Turn Pot VR2 fully counterclockwise to achieve full modulation.
Spread coil L16 slightly to increase dead key.
That's it. You're radio should dead key close to ten watts and swing close to 30.
I left the radio keyed for over an hour connected to a dummy load, with a modulation tone applied to the Mic input, and the IRF520 remained cool to the touch.
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