[Amps] Solid State HF High power linear amps

[Will Matney]

Sam,

The 2SC2879's are what I'm getting at and the MRF-454, 2SD1466, etc.. These are not what's needed for a high power amp and to me ought to be used for no more than 2 or 4 if your going to run them. When the big ones are built using these, there's never any filtering and they bleed a far piece each way. There's only one way to clean them up and that's filtering plus running them at the right class. Also, not overdriving them which happens a lot. Most of the junk being made with these semis are ran class C and if they're ran as advertised AB, they dont even regulate the bias. Now I agree that a good clean amp can be made with semis but it takes way more than the amps in mention. These are the ones I'm speaking of being dirty amps.

It's a better idea as you say to talk about IMD and harmonics differently instead of using the term splatter. They are beasts of a different type all together. Both together make a dirty amp.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 3/29/05 at 2:31 AM S. J. Blackwell wrote:

>I do not consider harmonics splatter. Harmonics are harmonics. Splatter
>is 
>IMD, the worst 5th and higher order. Pi-L nets do nicely for harmonics,
>but 
>you can overdrive a  tube amp and get all the splatter you want Pi-L or
>no. 
>This is particuliarly true for tetrode grid driven amps. Simply consider 
>your switchable filter your transistor Pi-L. Perhaps we should drop the
>word 
>splatter for this discussion and use IMD and harmonics. They are not the 
>same, not very well correlated.
>>
>>Every amateur amp using solid state transistors I've seen has a
>switchable 
>>filter in the output. Plus, from experience on running transistor amps, 
>>they did in fact splatter worse than a tube amp where the pi or pi-l tank 
>>acted as a low pass filter. Harmonics is what's in question and what I 
>>consider splatter along with IMD included.
>>
>If you want to go high power mobile with a 12 volt system, then you are 
>screwed splatter wise, but you sure can control the harmonics as the are
>not 
>in the bandpass of the filters.. Accept the IMD or go to an inverter and 
>higher voltage for either a tube or a higher voltage MOSFET. Forget the
>low 
>voltage (mostly bipoler transistors) for base or mobile if you want high 
>power and keep the splatter down. Harmonics may bother the guy 2X or nX
>you 
>freq but splatter sure will not. We were talking about high power amps 
>anyway. Using a bucket full of 2SC2879's is poor enginering. I have only 
>seen these on E-Bay for mobile and "base amps", usually with no harmonic 
>filters\, but with a stupidly added receive preamp built in. Usually 
>advertised as "10 meter amps".
>
>>Go look at how many transistors are rated for 50 volts as compared to
>12-18 
>>Vdc for 2-30 MHz. There's more 12-18 Vdc I've seen from every
>manufacturer. 
>>50 volt semis are great for a base amp but for a mobile which supplies 
>>12-14 Vdc, you'd need an inverter or something to step it up. That's why
>I 
>>think the 12 V versions are more popular and more part numbers from the 
>>manufacturers.
>>
>73,
>Sam, W5LU
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