King KT-76/78; all series
The KING KT-76 and KT-76A transponders are industry standards. Tens of thousands of them are flying today. King also produced the KT-78 and the KT-78A as lower altitude (certified to 18,500 feet) Class II versions. The KT-76A and the KT-78A are later models with some minor improvements. The latest model, the KT-76C, is awesome. It features sequential push-button squawk code entry, a single button user-preset VFR 1200 feature, and a super bright orange-red gas plasma display. All are very fine units.