On Aug 2, 2006, at 10:30 AM, Tom W8JI wrote:
>> 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.
Roughly a third of the autopsies I've done on 3cx1500A7s tells me
that it is capable of UHF parasitic oscillation. My guess as to why
is because at 300MHz, there is around 4000-ohms of XC feeding back
from the output to the input.
>
> 73 Tom
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|