Carl Built 400HDHG Amplifier / 2SC2879 Wattage Help

[Shadetree Mechanic]

Capt Crunch posted:
"One pushed 2X2290s @ 160 watts pep into it and it did 675 watts PEP."

let's look at the gain of the 4X2SC2879. the minimum gain of a 2SC2879 is 13 db. with a power multiplier factor of 20X. in a transistor rated for 100W PEP output at 13 db. the required drive input for full modulated power output is 5W PEP., i.e., 20X 5W PEP = 100W PEP X 4X2SC2879 = 400W PEP. with 20W PEP input. now let's get crazy and increase the drive input to 40W PEP input and use your input and output figures of 160 and 675. the power multiplier factor is now reduced to 4.28175X. this ratio translates to a reduction in gain of all four transistors from 13 db. to 6.25 dB., a whopping 6.75 dB. below the 2879's minimum rated gain. at a reduction of only 1 dB. the transistors are already 1dB. into the compression curve/region and we still have an additional 5.75 dB. loss in gain to account for. the devices have moved out of and beyond the active region and are in deep saturation. if you drive them like this then with regard to saturation, that ship has already sailed. now the question is not if she's gonna blow, but when.

in addition, the other bad thing with regard to running them like this is that if you should have any kind of an antenna or feedline problem between the amplifier and the antenna (an open or short) then you have completely lost the ability of the 4X2879 transistors to shrug off any swr conditions that might result in destruction of the transistors from a 15, 20 or even a 30:1 swr.. that safety factor is gone.

and all of this is for what? for an extra 2.2 dB. of gain over operating them at 400W PEP which is sad because under real time conditions no one is ever going to notice the difference in signal strength.

dB. gain = 10log (power output divided by power input)
dB. loss = 10log (power input divided by power output)

Bump for good info.

 

[Lost Ram]

If it interests anyone go look at ham amps with the 2sc2879 and the cb amps with 2sc2879 video watt tests. For some reason when I build one I get pretty much what the data sheet says when I drive each transistor with 8-10 watts, good thermal tracked biasing, and along with a good LPF. Sure I can ramp up the voltage some a get the anticipated % gain for the most part but it no where near 2x or more then the data sheet. Yes, I am stirring pot and being a troll!!!!! LOL. But, for real thats what I get. Even My 50V 160-10 meter BLF188 build with LPF was spot on with the data sheet. What do y'all get building with good biasing and filters??????