The recent discussion about a replacement transistor for Q503, the PA transistor in a PPL-6060 UHF mobile transceiver included a suggestion that the Motorola MRF648 could be used as a replacement for the EFJ 576-0004-062. While that transistor is physically the same as the MRF644 which I recommended, its drive requirements are greater. I chose the MRF644 as a replacement for the original EFJ device not only because I found a cross-reference for it (576-0004-062=>SD1088=>MRF644), but also because it is compatible with the Q502 driver transistor 576-0004-061, which produces 5W of drive to Q503. For that reason, the MRF648 may not perform as expected in the PPL-6060 radio. In particular, these PA transistors may produce spurious signals if driven well below the design levels. Choose wisely...
Here are the ratings of the four Motorola transistors in that series, as shown in the Motorola RF Device Data book: MRF641 15W output with 2.1W drive MRF644 25W output with 5.0W drive MRF646 45W output with 12W drive MRF648 65W output with 21W drive All of the above transistors have identical packaging, voltage rating, and frequency response. 73, Eric Lemmon WB6FLY
