[AMPS] Re: 2m legal limit amps

[Ian White]

Barry, K8SD asked:
>
>Has anyone tried to water cool a 4CX250R,B running 2200 V,Ep, 400V Es, -80V Eg.  
>I have seen this done on 2C39's with dramatic results.  some 60 to 70% more 
>overhead?


Yes, a ZL has tried it and it does work, though the benefits are not as
great as for 2C39s. I think that's basically because the 2C39 cross-flow
air cooler is rather ineffective, leaving the tube under-cooled at high
power inputs. 

The normal axial-flow air cooler is already very effective, so water
cooling wouldn't make such a big improvement.

Another point is that 2C39s are generally used in cavities, so the anode
cooler is substantially dead to RF. This makes water cooling much easier
because the plumbing doesn't get involved with the VHF/UHF tuned
circuits. In contrast, 4CX amplifiers generally have the anode cooler
live to RF. You'd have to run the water tubes along the anode line and
take them away from a low-impedance point somehow.



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

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