jeremy-ca wrote:
>
> ----- Original Message ----- From: "Steve Thompson" <g8gsq@eltac.co.uk>
> To: <amps@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@eltac.co.uk>
>>> To: <amps@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.
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
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