[Amps] 4CX250 IMD

[Steve Thompson]

>>>>> At Ep of 1500 in AB1 3rd/5th is -30/35. However at 2000V it slips to
>>>>> -23/27.
>>>>
>>>> At what power and efficiency?
>>>>
>>>> Steve
>>> 250/245 ma and 262/470 W PEP Note they specify PEP. There is also a
>>> "worst case" 3rd order line entry of -29/21dB.
>>
>> Single tube or pair?
>>
>> Thanks, Steve
> That rating is for AB1 SSB service, 2KV@ 250ma is the listed typical 
> operation for one tube as with all in the straight 4CX250W family.
Pushing a 4CX250 to 470W pep output is absurd and it's no surprise 
that the IMD is awful. It's totally unrepresentative of proper use 
of the tube in linear operation.

Collating all the info. we've been through, looking at pep from a 
single tube and IMD3 ref one tone:

STC data says -30 at 285W
Eimac data says -30 at 262W
My amps measured -30 or better at 250-300W
GW4FRX measured -30 at 250W
GW4FRX measured -22 at 250W with screen supply having 150 ohms 
source resistance.
Carl measured -22ish with a gas tube screen supply, source 
resistance probably >300 ohms
Eimac data says -21 with massive overdrive

There's no inconsistency here, and no reason to doubt anyone's 
measurements. It's clear what the tube's linear capability is, and 
it can do better if backed off and biassed/loaded for optimum.

Steve