[Amps] 4CX250B and data sheets in general.

[Ian White GM3SEK]

  wrote:
>In a message dated 4/4/06 8:01:09 AM Central Daylight Time,
>amps-request at contesting.com writes:
>
><< But then we have the Eimac data sheet for the 4CX250R, which includes a
> set of operating conditions to squeeze 400W PEP out of a single tube.
> Not surprisingly, the 3rd-order IMD then increases to only -23dB
> "referred to signal level" (which I take to mean "below PEP"; if so, it
> equates to only 17dB below either tone). In other words, Eimac were
> recommending operating conditions that produce totally unacceptable
> levels of IMD.
>
> This data sheet has had several bad consequences:
>
> 1. It led many users to be too greedy for output from 4CX250Rs.
>
> 2. It gave some users to claim that -23dB 3rd-order is OK "because Eimac
> recommend it".
>
> 3. It gave the entire 4CX250 range a bad reputation for "-20dB IMD".
>  >>
>
>Do not blame the data sheet for a poor design. Data sheets are as much of a
>sales tool as they are an engineering tool. As such, the tube tabular
>parameters for a given class of service are given to put the tube in the best
>competitive light possible. So unless the data sheet gives you specific 
>performance
>specs for the given set of tabular parameters,

This particular data sheet did exactly what you say: it specified the 
operating conditions, the PEP output and the levels of IMD to be 
expected. In doing so, it implied that the company endorses such IMD 
levels in a linear amplifier.

Marketing plays a big role in data sheets (Dilbert is non-fiction) but 
in the end it's a corporate responsibility, and the corporate image that 
suffers if they get it wrong.

Once the data sheet is published, there's no going back, so over the 
years this particular set of operating conditions has contributed much 
to debase the meaning of "linear".

Numbers of people on this list have heard the results on the air - and 
they *will* get you yelled at. I doubt if Eimac originally intended its 
name to be used as an excuse for poor signals; but that has been the 
result.


-- 
73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek