[Amps] AL811, AL811H or AL572 mods to 6m

[Tom W8JI]

> The original capacitors are just fine if you have a tube 
> load
> impedance of 400-600 ohms. The added coil creates an 
> L-network which
> transforms the approx 4000 ohms of the 3-500Z down to that 
> value.
>
> As I mentioned, this technique is covered in any recent 
> ARRL handbook
> in the HF amplifiers chapter. The example they give is for 
> ten meters,
> but the principle applies equally to six or any band for 
> that matter.

The only problem doing that is stability.

It generally works OK to do that with a very stable tube 
like a 3CX1500A7 or 3CX800A7, but tubes with long grid leads 
can get a bit squirrelly.

73 Tom