[Amps] How to improve efficiency
Ian White, G3SEK
G3SEK at ifwtech.co.uk
Sun Nov 30 20:12:07 EST 2003
Ve6wz_Steve wrote:
>I have a HB 4-1000 amp, GG, 6 kv on the anode, tuned input, PI output.
>
>Output (and input) is awesome on 40m, but I cant get the same steam on
>80m.
>I realize that efficiency can be variable from band to band, but what
>can be done to improve single band (80m)performance ??
>Where do I start ? I presume changes to the tank circuit may be in
>order??
>I DO have sufficient loading capacitor range.
>Any suggestions.
Tune and load on 40m, just as you like it, and then switch off and
disconnect the whole amp.
Connect a 5-10k trimpot from anode to the nearest chassis ground, using
broad, flat leads to minimise stray inductance. Looking back into the
output with an antenna analyser, adjust the pot for a perfect 50-ohm
match (without touching any amp controls). The pot setting equals the
optimum load resistance.
Now switch to 80m, and try to re-tune and load for the same perfect
match (don't touch the pot). You probably can't - which is why there's a
problem on 80m - so you'll need to adjust the inductance.
If it still isn't working, there are also heavier-duty spreadsheet
methods on my website.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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