Peter,
That's about it. It's mainly over the FCC trying to prevent 11 meter amps.
That was one of the dumbest moves they ever did if you ask me. They
ought to have known they would have been built anyhow.
On a grid driven tube, the gain is much higher than on a G-G cathode
driven configuration. If the FCC hadn't screwed this up, amateur transceivers
most likely would have been built with a lower transmitting power. That
would have put all the power components in an amplifier. Now to run a
grid driven amp, you have to use an attenuator in the input. I've built
several of these, and the input tuning I used was a matching transformer
tuned by a capacitor. The attenuator is before this arrangement.
Best,
Will
*********** REPLY SEPARATOR ***********
On 8/3/06 at 9:24 AM Peter Chadwick wrote:
>Hsu asked:
>>Why many Amplifiers using cathode driven?why not grid ?<
>My answer ( and it's doubtless open to argument) is two fold.
>First, the majority of transceivers are of the 100 to 200 watt output
>level, so a grounded grid triode is a convenient way to go. Secondly, the
>FCC rules, certainly until recently and maybe still, for I don't know if
>they've implemented the changes they proposed, prevented manufacturers
>from selling in the US amplifiers with more than a certain amount of gain
>- the idea being to prevent CBers using illegal power. (And a vain hope
>that was!) So it made sense in power distribution to run about 13 dB of
>gain in the amplifier from a 100 watt driver, while for a lot of
>people,100 watts is a good power level to run anyway. And 13dB of gain in
>grounded grid is a reasonable number to get.
>Given all this, the grounded grid triode amplifier is cheaper to produce,
>because you don't need a screen grid supply, and generally happens to be a
>bit more linear than tetrode, which you would need for a grounded cathode
>amplifier. I discount a neutralised triode grid driven amp these
>days......too complicated and thus expensive.
>
>The downside is that you need tuned circuits in the cathode for decent
>linearity - I was always surprised at the 30L1 not having those.
>
>The grounded cathode tetrode with grid swamping isn't to be discounted,
>but can have the linearity improved with negative feedback, without too
>much difficulty.
>Does this answer the question?
>73
>Peter G3RZP
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