>>>>>> The 4CX250 family is another very poor choice. They were not
>>>>>> developed for
>>>>>> SSB use and the linearity is only in the mid 20's under the best of
>>>>>> conditions. This includes the 250R. Ian, G3SEK/GM3SEK, has written
>>>>>> extensively on that subject and even developed a set of bias
>>>>>> regulators to
>>>>>> at least improve the IMD a bit.
>>>>>
>>>>>
>>>>> I think they can do better linearity than that - the amps I built have
>>>>> all done so at 250-300W/tube. The STC data sheet for 4CX250B gives IMD
>>>>> figures under the typical operating conditions. At 2kV, 325W pep
>>>>> output
>>>>> they give IMD3 -30dBc and IMD5 -50dBc. That's in line with what I've
>>>>> seen.
>>>>>
>>>>> Steve
>>>>
>>>>
>>>>
>>>> Which method of testing do you use and did you read Toms recent post?
>>>> There is a huge difference between true real world IMD and the
>>>> advertising departments way of rating it.
>>>
>>> My driver ran around -55dBc IMD3 and I never tried to measure IMD5, it
>>> was off the screen. I use dBc to mean referenced to a single tone
>>> (assuming that's what you mean by 'method of testing').
>>>
>>> Steve
>>
>>
>>
>> Try the 2 tone method which was the way I was taught many years ago when
>> proofing military equipment. Both are acceptable as long as you are
>> aware of the differences and can reference one to the other when making
>> statements.
> I'm sorry if we ended up at cross purposes. I was talking about 2 tone
> measurements - just like when I was designing mil gear.
>
> Steve
In that case I suggest that you recheck your measurement calibration as
Eimac references to a single tone which gives an inflated result.
Please read Toms posting from this morning, it explains in detail.
Carl
KM1H
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