[Amps] New SB-200 owner

[jeremy-ca]

----- Original Message ----- 
From: "Steve Thompson" <g8gsq at eltac.co.uk>
To: <amps at contesting.com>
Sent: Thursday, September 27, 2007 9:59 AM
Subject: Re: [Amps] New SB-200 owner


>
>
> jeremy-ca wrote:
>>
>> ----- Original Message ----- From: "Steve Thompson" <g8gsq at eltac.co.uk>
>> To: <amps at contesting.com>
>> Sent: Thursday, September 27, 2007 9:36 AM
>> Subject: Re: [Amps] New SB-200 owner
>>
>>
>>>
>>>> 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.

Carl
KM1H