[TenTec] Omni power xistors

[Frank alforo]

The eminent unavailability of the MRF458 RF power transistor used in the 
Omni VI+ rigs is a serious consideration for those of us who plan on keeping 
this transceiver indefinitely. Although the track record for failures of 
this component is extremely low, it is still a cause for concern.

It appears that the Motorola MRF454 is indeed a suitable replacement for the 
MRF458 transistors as reported by W6LX a few days ago. Both use the 211-11 
package. The MRF454A and the MRF458A are respectively identical electrically 
but are in a different package. Do not use these.

The 1983 Motorola data book shows that the MRF454 is a somewhat more rugged 
transistor than the MRF458.
The MRF454 is spec'd at 20 amps continuous collector current and a power 
dissipation of 250 watts while the MRF458 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 MRF458 is spec'd at 70 watts for 5 watts of drive. The 1994 data book 
lists the MRF454 as a direct replacement for the MRF458.

The following transistors are 'identical' to the MRF454: 2N5460, 2N6459, 
CD7012, MRF420, S80-12, SD1076 and the SD1078. While The SD1405 is 
'identical' to the MRF458. I do not know if 'identical' means identical 
electrically AND physically or electrically only. I do not know who makes 
these.

MRF458 matched pairs are identified by a colored dot on the body. Identical 
colors indicate matched transistors. I do not know if the MRF454 was 
similarly identified.


If would be interesting if someone can determine availability of MRF454 and 
the replacements, the SD1405, as well as a possible cross-reference to the 
2SC types used by the yaecomwoods, and if matched pairs are available.

73 de Al, w6wqc






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