>
>On Fri, 25 Jul 97 21:42:09 -0700 Rich Measures <measures@vc.net> writes:
>>>Somewhere along the line Rich came up with a value of 25 ma grid
>>current
>>>for a pair of 4-250A's in AB2 grid driven service.
>>
>>Peter Chadwick said that was how much grid current he ran.
>>
>>>Now, I dont see that
>>>number in any literature here; the closest is in a 1964 ARRL Handbook
>>>where they rate 10ma PEAK at 3KV Ep operation.
>>>But didnt Rich also say that only the 4CX1500B and 4CX600J were rated
>>for
>>>AB2? What gives here anyway?
>>
>>There are two flavors of Class AB2 grid-driven operation. Non-linear,
>>
>>and linear.
>
>
>You are wrong Rich. It is More Linear and Less Linear.
>
Word games. Linear means an amplifier that is UNlikely to get one tarred
and feathered at the next ham swap meet.
...snip...
>>>According to RCA, way back in Dec 1954 Ham Tips, is that a 4-250A
>>in
>>>AB2 requires 4.5w of peak drive. Yet at the same Ep the output is
>>520W
>>>vs 370W in AB1. I would think that a 41% power increase would rate a
>>>little wiggle...dont you? On top of that the Es requirement drops
>>from
>>>500V to 300V.
>>>
>>To make a 4-250A work at its emissive capability in Class AB1,
>>SSB-mode,
>>I would use 800v on the screen and 4kV on the anode. I'm guessing
>>that
>>pep output would be about 900W.
>
>
>Sounds like an excellent candidate for screen meltdown IMO.
>
Why would a screen V that is within the Eimac ratings cause a 'screen
meltdown'?
...
>>It's harder to build a dirty AB2 amplifier than a cleaner AB1
>>amplifier.
>>With AB2, you need a regulated grid bias supply. With AB1, the bias
>>supply furnishes zero current so regulation is not needed.
>
>I wasn't aware that a regulated bias supply was that complex and
>difficult.......
Is a regulated bias supply no more complex than an unregulated bias
supply? I've built AB1 amplifiers both ways and I discovered that a
regulated grid bias supply makes zero difference.
>I would also suggest one for AB1 just in case you develop a bit too much
>drive while tuning, debugging, etc.
>
Why bother? If you get a bit of grid current, the grid bias V
temporarily increases a bit and goes back to zero when you turn the grid
bias V up to where it's supposed to be.
Rich---
R. L. Measures, 805-386-3734, AG6K
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