Tom Cathey wrote:
>>They also say that IM product do not necessarily drop as drive is
>>reduced. It can actually be greater at lower power levels than at higher
>>power levels. IM products drop way down at one point midway in the power
>>range and then go back up again. They show a graph that is derived
>>mathematically and say that most tubes follow the graph pretty closely
>>to the predicted IM performance ratios of drive to bias amount.
>>
>
>
> Gary,
>
> Yes, I've read that too, but then I've read the opposite.. That statement
> above would make my question about using a chain of GG tubes running at
> 1/10th reduced ratings a poor idea. I'm a little confused cuz I see it
> written sometimes that for very linear operation, sometimes stages run at
> 1/10th their power ratings in class A. Maybe that's for special purpose
> receiver high performance preamps or something like that.
I think it's important to consider the difference between the class AB
biassing that we are all used to in our amplifiers, and true class A
which is usually reserved for specialist ultra-linear requirements. As a
simple rule of thumb, ultra linear class A operation will have the
maximum peak output power not much over 10% of the dc power dissipated
in the device, and the current in the device will not alter with signal
level.
Steve
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