>> The tube is being tested in AB1, ZERO grid current,
>> therefore Eimac is not
>> overdriving it.
>
> Wrong.
> It is certainly possible to overdrive a tube without grid
> current or excessive grid current. Odd-order products are
> caused by flaws or imperfections in the transfer
> characteristics, and having zero grid current does not
> prevent that.
I simply stated that EIMAC was not overdriving it in their test. Or dont you
give them credit either for knowing how to run tests?
>>They are simply showing the degradation when the tube is
>>run
>> at its TYPICAL rating of 2KV. I have no idea how they
>> computed the PEP; the
>> spec sheet is dated 1961 and the procedure may have been
>> different. If you
>> read back to my prior post I stated 2KV @ 245ma which is
>> only 490W INPUT.
>> Let us both agree that the PEP is a typo.
>
> Not true.
> Having two tones raises the PEP by a factor of four over a
> single tone. The way it REALLY works is:
>
> One tone by itself:
> average, peak envelope, and per tone is the SAME.
>
> Two equal level tones:
> 1.) Each tone is 1/2 the average and 1/4 the peak envelope
>
> 2.) Average is the sum of power of the two tones. This is
> the heating power and the power that would show on an
> average reading meter.
>
> 3.) Peak envelope power is four times the power of each
> tone, or twice the average power. This is the power that
> shows on a Peak Envelope Power meter.
Was the modern and accurate PEP meter being used at Eimac or were they using
1950's technology in 1961? Do you have documentation of their full test
procedure and instrumentation?
>
>> When run at only 1500V the IMD is acceptable. Im again
>> making the assumption
>> that the screen is VR tube regulated in Eimacs1961 test.
>
> Eimac only gives one particular set of test conditions for
> one test fixture and in general one particular setting that
> someone selected. There are an infinite number of variables
> involved, and we can't conclude based on the data published
> that the "IM gets worse as HV is raised".
Theoretically maybe but long accepted published data appear to lead to that
conclusion in light of the goal that more HV equals more power. Im more
interested in the real world of and not some cloud layer thinking.
>
> A statement like that is taking the data sheets far beyond
> what they really say. Even Eimac, if we take the time to
> read, warns users to test in the actual application and the
> data sheets only represent a few randomly selected operating
> points in one particular hardware configuration.
>
> What we find in an actual circuit can be much worse than
> Eimac shows, or it can be significatly better. It doesn't
> even have to follow the trends. As a matter of fact if the
> screen is regulated and adjusted to optimum values and if
> output power remains the same, and increase in HV almost
> always improves IM performance.
Too many optimums have to be met. Not practical in the real world builders
basement. Certainly very questionable with used tubes. And as stated the
ultimate goal is usually more power since it takes more money to raise the
HV. IMD is of secondary, or less, importance to Joe Sixpack who is
responsible for the trashy signals. Joe Sixpack does not read the Amps
discussions.
>> OTOH, I know of no commercial ham amp that runs any 4CX250
>> at 1500V and many
>> hams push them above 2KV which just makes matters worse.
>
> Not true. That statement is most likely based on either
> misunderstanding data sheets or not reading Eimac's cautions
> that the actual circuit needs tested.
>
Oh? so what SSB commercial ham amps are you aware of that run a 4CX250 at
1500V? Several commercial FM amps that have been ham converted do operate at
around the 1500V level. Most if not all QST/Handbook and similar ones run at
full bore.
And Ill repeat that some ham built amps exceed 2KV.
Carl
KM1H
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