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MRF-458 Final Replacement

(comments posted by W9GB to qrz.com forum)

TEN TEC OMNI-V Final AMP MRF-458 burned out several days ago, so I replaced them with 2SC2879, readjusted bias. It worked OK, except at the 10 meter band the RF output was 75 watts instead of 100 watts. Just in case somebody have same problem. MRF-458 is difficult to obtain. Niko -

The Toshiba 2SC2879 is a well known RF transistor as well …. The difference between the Toshiba 2SC2879 and the 2SC2879A is that the “A” version is RoHS compliant, and uses an Aluminum Nitrite insulator (color gray) on the header vs. Berillium Oxide (color white). The "A" part will have a RED dot after the "9" in die stamping. This Toshiba part sell for $33-$35 each at RF Parts.

The Motorola MRF-458 was also used in the Ten Tec Omni VI+ HF transceiver. Al, W6WQC provided these insights 10 years ago (December 2002) on the TenTec forums: http://lists.contesting.com/_tentec/2002-12/msg00383.html

The Motorola MRF-454 is indeed a suitable replacement for the MRF-458 transistors as reported originally by W6LX. Both parts use the 211-11 package. The MRF-454A and the MRF-458A are respectively identical electrically BUT are in a different package. DO NOT use these "A" parts.

BTW, M/A-COM continues to produce the MRF-454 !! The M/A-COM MRF-454 RF transistor is a current production and "off-shelf" part. Mouser has them for $55 each (cheaper in qty) with over 100 In Stock !! Mouser Part #: 937-MRF454

IN ADDITION, RF PARTS stocks both the Motorola and M/A-COM MRF-454 ($43-$45) and Motorola MRF-458 ($24) parts !! http://www.rfparts.com/transistors_MRF-TP.html == The 1983 Motorola data book shows that the MRF-454 is a somewhat more rugged transistor than the MRF-458. The MRF-454 is spec'd at 20 amps continuous collector current and a power dissipation of 250 watts while the MRF-458 is spec'd at a collector current of 10 amps and a dissipation of 175 watts.

Both have an identical gain of 12 dB, power out of 80 watts and 50 percent efficiency.

The MRF454 has higher maximum Vceo and Vcbo ratings.

The MRF 454 has a higher gain at 30 mhz: 90 watts for 5 watts of drive while the MRF-458 is spec'd at 70 watts for 5 watts of drive. The 1994 data book lists the MRF-454 as a direct replacement for the MRF-458.


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