----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Steve Thompson" <g8gsq@eltac.co.uk>; <amps@contesting.com>
Sent: Saturday, September 29, 2007 2:02 PM
Subject: Re: [Amps] 4CX250 IMD
>>>They are simply showing the degradation when the
>>> tube is run at its TYPICAL rating of 2KV.
>>
>> and at much higher output power. The IMD goes bad because
>> the tube
>> is being pushed to deliver too much power, not because the
>> HV is
>> higher.
>
> That is correct. People are comparing an entirely different
> set of parameters, not just a voltage increase alone.
>
> It is the output power increase that is largely responsible
> for higher IM, although a loose screen supply could
> contribute if the higher voltage starts to produce a more
> dynamically varying load on the screen supply.
What both of you continuously fail to understand is that the tube is being
run within its manufacturers published ratings. No amount of side stepping
can change that fact.
It is also an established fact that in commercial or home brew ham
amplifiers the tuning procedures emphasize tuning for maximum output while
keeping within the parameters established by the tube manufacturer. A 1000W
DC Input 2X 4CX250 amp is operated at 2000V@500ma yielding a single tone
output of approximately 600W or a PEP of your choice. Nowhere do they say to
reduce the power output to conform to some unknown or unestablished IMD.
Accept that simple fact and lets not draw this into some long drawn out
meaningless drivel on semantics or nit picking as some have a habit of
doing.
High quality commercial (non ham), military, multistage or super cathode are
not included in my comments. It just adds to the confusion.
Carl
KM1H
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