[Amps] Question: Ameritron AL-80A tuning

[Vic Rosenthal]

NW7US, Tomas wrote:

> Hi,
> 
> I am using an AL-80A and have need as an Army MARS and National Guard 
> Net  member to utilize frequencies far out of normal Amateur Radio  
> allocations.  I am finding it hard to get the Amp to tune on certain  
> frequencies "out of band" - I can get about 100 watts on those problem  
> frequencies.
> 
> I suspect that the filter netwoks in this Amp prevent it from being 
> used  too far out of frequency.  Is that true?

Check the SWR on your exciter.  If the SWR is over 2 or 3 to 1, then possibly 
the exciter output is folding back, providing less drive.  And this would 
indicate that the input pi nets are probably attenuating the drive that does get 
through.  So in that case, the answer to your question is 'yes'.  I'm not sure 
if it's possible to broaden these input networks, since it would significantly 
reduce the input network Q, causing other problems.

You could retune the 80 or 40 meter input network to reduce the SWR on 5 MHz. 
For example if you are an SSB only operator (God forbid) then you could center 
the 80 meter network at 3.9 MHz. or higher.  It would still work on the 75 meter 
phone band, but the SWR aboove the band would be lowered.

There is also an incorrect Q in the plate circuit.  For example, if you are 
using the 80 meter position to operate on 5 MHz, the Q would be lower than 
normal.  This would reduce harmonic suppression, but should actually increase 
efficiency slightly.  If the plate tuning and loading controls are not at 
extremes, then the problem is not related to the plate tank.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco