Jim I'm not sure what you are looking for here. It is highly desirable to use parts with a second source. That way if the factory burns down you are not put out of business. That being said with RF parts the second source is seldom identical hence the reference to the manufacturer. Manufacturing processes differ from factory to factory. Sometimes the difference will be noise or something you will have to look at a Smith chart to see. This makes it difficult to interchange.
A major problem with using quads (two push-pull pairs) is current sharing. If more current flows in one transistor than the others it will get hotter and possibly be pushed beyond specifications leading to failure. Failures may 'domino' leading to secondary failures. Fortunately FETs have a negative coefficient of resistivity which makes them much easier to balance, hence their popularity in newer amps. 73 Fred, AE6QL -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Robbins, James Sent: Friday, August 17, 2012 3:21 PM To: [email protected] Subject: [Elecraft] Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx I am wondering if anyone has an explanation for why the Elecraft KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to generate very similar power levels. The data sheets for each FET indicate that both brands are rated at 300-400 watts, support similar mismatches and run at similar voltage maximums. They have very similar specs all together. Perhaps our amplifier gurus could weigh in here. Much appreciated. 73, Jim Robbins N1JR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
