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??????

 

[Triple_7]

First may I say I love my 400HDHG Amp and Carl is good people. That being said, I have read on spec sheets 1 2SC2879 transistor max in says 10 watts PEP each. Carl says on his website about the amp "400 4 hg 2879, Class C bias, fan cooled. Max amp draw 110a, install recommended with 4ga wire and 125a fuse. Max input carrier of 10 w or 175w max carrier from amp. Max peak input 150w". I also asked him again later on and he replied "Key amp around 180 max and keep peak in amp around 100 watts". Also there are review videos of the 400hd with an "FCC" radio and then usually hook up a Stryker 955 doing 80+watts pep. When they hook the 955 up they say that it was about half the power this amp likes. One pushed 2X2290s @ 160 watts pep into it and it did 675 watts PEP. If true, how is that possible. I understand how high people have had these transistors but is it possible to talk for periods of time with no issues that high? Is there something they do and/or the amps class that makes that possible, or should I just follow the transistors specs when using mine? Right now I am using a stock Galaxy DX979 doing about 30 watts PEP. Trying to decide if I should get a 1x or 2x 2290 driver for the 400hd. Thanks in advance. Here is my amp at Carl's bench.

i dead key my carl built 400hd at 7.5w and get 75w out or 10 in gets 100w out, my swr is 1.1 with the box on, it gives up 800w to 850w modulating.

 

[SuperLid]

i dead key my carl built 400hd at 7.5w and get 75w out or 10 in gets 100w out, my swr is 1.1 with the box on, it gives up 800w to 850w modulating.

800-850 measured with what? What mode? What is the level of the second and third harmonics?

 

[SuperLid]

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??????

Yes you are, for real.