[Amps] Price per Watt Conversation

[Roger (K8RI)]

Not necessarily true now days.  Predistortion may actually  "clean up" a 
signal so the amp might actually have a cleaner signal out than the 
driving signal.
As to the ALC driving problem, that appears to be one companies rigs 
when operated at reduced power.  My FT5000 does not have that problem 
and it's driving a high gain Tetrode.  I can also run class A without 
overheating.

If you look at the ultimate final tube characteristics the tube, may, or 
may not have good IM. Much depends on how it's tuned up, how it's 
biased, and screen voltage / current if applicable.

73, Roger (K8RI)

On 4/25/2017 10:19 AM, Thomas Walsh wrote:
> Keep in mind the fact that one could have the cleanest amp and even with
> nfb, alc etc. applied, it still only amplifies whatever is on the input.
> What goes into also goes out of but now amplified. So if your exciter is
> dirty, you will have a dirty output! We now know that the current group
> of overpriced rice boxes are dirty as heck, and they even put out 100+w
> spikes that can damage any amp -tube or ss even though the drive level
> has been set low, it's the power level dac that must update every time
> it keys. They all do it...especially the 10,000+ dollar rigs. All this
> talk about imd etc., is usually caused by the exciter not the amp! On
> any amp design with any gain factor, if one keeps the exciter sig clean,
> at a conservative level it will automatically be clean. No alc is needed
> today because the radios do all the alc-ing, the amp is only a
> goes inta, goes outa. Alc and ndb only degrades the performance of
> the amp. This is why the older hybrid radios which are analog in drive
> control, never have a problem! It's when they hook up that 13K$ rice box
> do they have any imd and/or drive problems. Perhaps try brown rice, it
> may have some other effect.  Tom W2CO
>
>
>
> On Tue, 2017-04-25 at 13:24 +0000, Catherine James wrote:
>> Thanks, Jim.  I am learning something new here every day.
>>
>> I've been clear for some time on the fundamental conflict between good linearity (indirectly creating good IMD) and efficiency. With the last couple of days of discussion added, I now see that there's also a fundamental challenge in getting good efficiency and good thermal handling, and that the negative feedback solution isn't necessarily practical for some designs.
>>
>> The ideal amp would be highly efficient for lower power draw and minimal need for heat-sinking, have excellent linearity and IMD, use cheap devices, and support ALC, voice compression, and 100% duty cycle modes.  Looks like a square circle. :-)
>>
>> 73,
>> Cathy
>> N5WVR
>>
>> Jim Thomson <jim.thom at telus.net> wrote:
>>   
>>   ###  NFB =  Negative feedback.  3 db of NFB means you also reduce the gain
>>   of the amp by 3 db.  On paper, to achieve say a 10 db improvement in IMD,  you require 11 db of NFB.
>>   
>>   ##  6 db of NFB on a SB-220  means you now require quadruple the drive
>>   power.   NFB will work on a SS amp, since the gain is sky high  to begin with.
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