Featured: MRF454 and MRF455 transistors on eBay.
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Many solid-state HF amplifiers designed around a 12.5 V supply use bipolar RF power transistors, and the MRF454 and MRF455 are familiar part numbers in that kind of equipment. When a transistor fails, builders and repairers go looking for replacements, and eBay is one of the first places they check. It is also a place where knowing the genuine part's published data really matters.
What MACOM lists
MACOM describes the MRF455 as designed for power amplifier applications in industrial, commercial and amateur radio equipment to 30 MHz. Its product table lists a frequency range of 2 to 30 MHz, a bias voltage of 12.5 V, output of 60.00 W, gain of 13.00 dB and efficiency of 55%. The datasheet adds a gold metallization system for high reliability applications, a continuous collector current of 15 Adc, total device dissipation of 175 W at a case temperature of 25°C, and a collector-emitter voltage of 18 Vdc.
The MRF454 is listed at a higher output. MACOM's table gives 2 to 30 MHz, 12.5 V, output of 80.00 W, gain of 12.00 dB and efficiency of 50%, in a flange ceramic package. The datasheet title reads The RF Line NPN Silicon Power Transistor 80W, 30MHz, 12.5V, and the case is listed as CASE 211-11, STYLE 1. Both parts still appear on MACOM's site with ordering options.
Why eBay buyers need to be careful
Popular RF transistors attract copies and relabeled parts, and a counterfeit can look right while failing to deliver the power or survive the conditions of the real device. A few habits reduce the risk:
- Compare the package and markings in the listing photos with MACOM's datasheet, including the case style.
- Prefer sellers who photograph the actual parts, with a solid feedback history and a return policy.
- Be wary of bargain multi-packs of supposedly new parts at prices that look too good.
- Test before trusting. Try replacements at reduced drive into a dummy load, and watch current and heat before running full power.
Replacing transistors in an amplifier
Push-pull amplifiers use their transistors in pairs, and many repairers replace them as matched pairs rather than singly. Check the bias setting after replacement, and pay attention to heatsink contact and mounting, since a dissipation rating given at a case temperature of 25°C assumes the case is kept cool. MACOM warns that exceeding any one or combination of the maximum limits may cause permanent damage to the device, and that it does not recommend sustained operation near those survivability limits.
Keep the original parts until the amplifier is running well on the replacements. They are a useful reference if the new transistors turn out not to match what came out.
And a reminder whenever amplifier power is discussed: external linear amplifiers are not legal for use on CB radio. These parts belong in legal amateur, commercial and industrial equipment.
Where to get it
Browse current listings: MRF454 and MRF455 transistors on eBay.
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Educational reference only. Always verify all values independently against your specific device datasheet and build documentation. Working on RF and high-voltage equipment carries real risk.