>> From: yo3ctk <yo3ctk@alltrom.ro>
To: <amps@contesting.com>
>> Date: Tue, 22 Jul 97 14:48:13 +0000
>
>> Oh boy...I really hope I will not regret this.....
>:-)
>
>> For instance, EIMAC 4CX1500B. According to the manufacturer,
>> this tube is "specifically designed for exceptionally low
>> intermodulation distortion". Its typical operation is class AB2,
>> grid-driven service for frequencies below 30 MHz. Indeed, performance is
>> good: -40 dB 3rd order IMD, for 2750 V DC plate voltage and 1100W power
>> output. In this conditions, DC grid current is 0.95 mA for -34 V grid
>> bias.
>
>We can add ANY tube that can tolerate grid current to that list.
>Some tubes are better than others, but by careful design virtually
>all tubes that allow grid dissipation can be used in AB2 grid driven
>service.
>
>For example, the 4-1000A had an extensive article describing either
>AB2 or AB1 RF PA operation.
>
A friend of mine built a (2) 4-1000A Class AB2 amplifier. The screen V
was only 500V, so a moderate amount of grid-current was essential to
achieve the rated anode current. The amplifier was a virtual garbage
generator. The solution: Increase the screen voltage to 1000V so that
no grid current would be required to produce the rated anode current.
>Just because the typical operating guidelines do NOT list a certain
>class, it does NOT necessarily exclude that class.
>
Under a hundred watts from a grid-driven 3CX3000A7 in Class AB1---3000w
of drive needed for a 3CX3000A1 in g-g service---ummmmm, no thanks.
Rich---
R. L. Measures, 805-386-3734, AG6K
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