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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