pills
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- Technical Helper
- Posts: 78
- Joined: Saturday 21st Aug 2004, 16:17
- Location: Louisville, KY USA
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Um, there is more than one manufacturer making RF power transistors, and more than one type made by each of the folks who do.
And the power rating on the transistor's specification sheet is not the whole story, either. Some amplifiers using two so-called "60-Watt" transistors will deliver no more than around 130 Watt voice peaks. A different design using the same two parts may deliver close to 200 Watts peak. The parts that are wrapped around those "pills" have a lot to do with the power that you'll see. The choice of a wattmeter has a big influence, too. Any RF wattmeter that has been calibrated correctly should show more or less the same thing on a steady, unmodulated "dead" carrier. Where they will start to read differently, one from another, is when you modulate the signal. The "swing" reading that you'll see with voice modulation can vary by as much as three-to-one or more, from one meter to another.
It's not like the tachometer on a vehicle engine, where everybody uses the same basis to calibrate a reading. Some wattmeters will say "Peak Reading" on the front, and still only read 3/4 or so of the actual peak power.
73
And the power rating on the transistor's specification sheet is not the whole story, either. Some amplifiers using two so-called "60-Watt" transistors will deliver no more than around 130 Watt voice peaks. A different design using the same two parts may deliver close to 200 Watts peak. The parts that are wrapped around those "pills" have a lot to do with the power that you'll see. The choice of a wattmeter has a big influence, too. Any RF wattmeter that has been calibrated correctly should show more or less the same thing on a steady, unmodulated "dead" carrier. Where they will start to read differently, one from another, is when you modulate the signal. The "swing" reading that you'll see with voice modulation can vary by as much as three-to-one or more, from one meter to another.
It's not like the tachometer on a vehicle engine, where everybody uses the same basis to calibrate a reading. Some wattmeters will say "Peak Reading" on the front, and still only read 3/4 or so of the actual peak power.
73
- rubbandman
- Dead Key
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- Dead Key
- Posts: 14
- Joined: Tuesday 13th Jun 2006, 17:31
- Location: MOUNT GAMBIER SOUTH AUSTRALIA
rubbaband man says 2879 that would be 2sc2879. Your reference to 455 would be MRF455. Both of these pills are virtually identical and in practice would deliver very close to the same power in the same circuit.
If you are after replacements stick with the '455.
These transistors could be expensive so try to get a couple of disused motorolla maxar80 low-midband vhf radios and salvage the pills from them. with any luck they will be that close to the same that they will work as good as new ones.
Gotta be worth it as if u are crafty enough u can pick old radios like that up for nothin. I got 4 of them just lyein there 4 the same reason that i got for free. And also breifly the output transformer in an amp. will also get quite hot in use and this will limit the power output. antway cheers from daz in auz.
If you are after replacements stick with the '455.
These transistors could be expensive so try to get a couple of disused motorolla maxar80 low-midband vhf radios and salvage the pills from them. with any luck they will be that close to the same that they will work as good as new ones.
Gotta be worth it as if u are crafty enough u can pick old radios like that up for nothin. I got 4 of them just lyein there 4 the same reason that i got for free. And also breifly the output transformer in an amp. will also get quite hot in use and this will limit the power output. antway cheers from daz in auz.
pill power ratings
MRF455 is 60 watts , SD1446 is 70 watt , 2SC2290 is the 80 watt , 2Sc2879 is the 120 watt The most popular 100 watt is the SRF3800 . There are others that are rated at 100 watts . These spec,s are provided by RFparts in the back on there printed catolog . these spec,s also do not rflect the actual out put as it may be higer or lower depending on the device construction and freq used . RF parts is the best source for these transistors , next would be West gate parts
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