[AMPS] Switches

[Ian White, G3SEK]

Tom Rauch wrote:
>
>The key word is "right". Some people think unregulated voltages 
>aren't a problem. The fact is, tetrodes are dirty enough when 
>properly regulated. Look at the IMD comparisons of the ETO amp 
>with a tetrode compared to an AL-800H...which is a low dollar 1500 
>watts SSB duty-cycle amplifier.
>
I wouldn't say that the screen supply in the 91/99B is well regulated
(only zeners) so that amp doesn't necessarily show us the best IMD
performance the 4CX800 is capable of.

Likewise Eimac's recommended operating conditions for the 4CX250R have
given tetrodes a bad name, by being too greedy for power output and
accepting - promoting, even - very poor IMD performance.

Even so, I think it's being far too sweeping to imply that all tetrodes
have worse IMD performance than (all) triodes. There are far too many
other factors in the design and operation of an amplifier.

>Even if the operating problems of getting a customer to load the 
>tetrode correctly are solved, and you accept the reduced IMD 
>performance 
[hmmm...]
>and fact that tubes may be a future problem (a tetrode 
>is harder to substitute with another  tetrode than a triode is with 
>another triode), 

There's no doubt that tetrode amps are much less "plug-and-play" than
triodes. It's easier to get things wrong, either at the design stage or
in operation. But if you do get everything right, a tetrode can give
good IMD performance.


>you still haven't solved the bandswitch problem.
>
Which all tube amps share alike.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.com/g3sek

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