Steve Thompson wrote:
>
>>>I could be very pedantic in specifying that I'd made linearity
>>>measurements on a 4CX350A, and someone might gain the impression that the
>>>figures only applied to that variant, when they will apply just the same
>>>to 4CX350F.
>>>
>>>
>>Whilst the 4CX350A and 4CX350F differ only by heater voltage (and so one
>>would assume have the same linearity), the 4CX350FJ is different, in
>>that it is designed for low intermodulation distortion - i.e. high
>>linearity.
>>
>>
>
>Eimac only say 'improved IMD..' without quantifying it. The data I have
>doesn't quote any figures for the '350A to give a starting point, so the
>'350FJ could have any linearity Eimac wants to give it and meet the
>description, especially as the 'typical' figures are given at different
>powers for the two types.
>
I've not checked the data sheets, but if Eimac put linearity figures
under two different conditions, it makes it hard to compare how much
better the FJ is than the F.
I'm not sure whether or not you have made the measurements, but you
spoke of figures, and someone gaining the impression these only applied
to the 4CX350A, when they would apply to the 4CX350F too. I feel that if
anyone takes the trouble to make linearity measurements on any tube, and
published those figures, they should state the tube model used, and the
conditions under which it was tested. Otherwise they might as well save
wear on their keyboard, and bandwidth on the internet, as the data is of
little value to anyone else.
>>So specifying the exact tube would not be being 'very pedantic' but
>>*absoluttely essential* for the numbers to have any sensible meaning.
>>Without the suffix, there would be no point in reporting the results.
>>
>>Would you agree or not?
>>
>>
>Would I agree if... what?
>
>Do I agree? No, in the context of a discussion on this reflector about amateur
>equipment I believe that the differences in linearity between the versions
>are immaterial.
>
Well I'm sure there are many who would pay an extra $10 for a tube if
the distortion products were 30dB lower, but few would pay $1000 extra
if the distortion products were 1 dB lower.
You and I obviously disagree quite a bit on this sort of thing!
>Likewise would you agree you would need to state the manufacturer of the
>tube too? It's highly likely the linearity might be different from one
>make to the next?
>
>
>
>Is it? If devices are sufficiently similar to warrant the same part number
>then it's likely they will have similar characteristics. Slight linearity
>differences might matter in meeting type approval specs. for broadcast
>equipment, but won't matter a jot in normal amateur operation.
>
If linearity is unimportant, is anode dissipation?
Lets make a statement, which I expect you might agree is reasonable, but
I think is not.
"The anode dissipation of a 3CX10000 is 10kW"
Well if you quantify that a bit more, and talk of the 3CX10,000A3, then
the anode dissipation will be 10 or 12 kW, depending whether you refer
to an Eimac
http://www.cpii.com/eimac/catalog/113.htm
or a Svetlana
http://www.g8wrb.org/data/Svetlana/pdf/3CX10000A3.pdf
tube. There does not seem to be a typo here, as the Svetlana data sheet
gives the airflow required for 12kW dissipation.
So in this case, two tubes with the same part number, from two different
manufacturers have anode dissipations differing by 20%.
Although I have not attempted to verity this, someone sent this to me
privately
"Heck, even the same tubes' part numbers by different manufacturers can
be incompatible (like the 572B)."
>I'll forward a copy of the '350FJ data for your website when I receive it.
>
I'd appreciate that Steve. We can't seem to agree on much, but I would
like the copy of the data sheet.
--
Dr. David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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