[Amps] How to improve efficiency

[Ian White, G3SEK]

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