[Amps] How do I determine Class

[R.Measures]

On Sep 1, 2004, at 8:22 AM, Jim Isbell wrote:

>  This is EXACTLY the answer I needed.  The amp uses a pair of 4-125As 
> and the screens are at "350V - 400V"   Plates at "2000V - 3000V" (but 
> no terminating resistor) so I guess that makes it a class AB1 linear.

Jim --  Class AB1 amplifiers always have a grid-terminating R because 
the grid draws zero current.  .

> The screen grids have several bypass caps to ground but no resistor.

A shunt resistor is needed to sink reverse screen-I.  Typically, about 
25% of normal screen-I is shunted by this resistor.

> The signal is fed to the control grids through the MB-40-L and the 
> plate circuit is prety normal..
>
> Just what I needed for my vintage shack linear.
>
> R. Measures wrote:
>
>> Jim -- If the tetrodes are being operated at roughly half of their 
>> max screen-V rating, they are likely being run in a non-linear mode.  
>> If they are being operated at their max. screen-V rating, and there 
>> is a grid-terminating R, they are probably operating in Class AB1 
>> linear service.
>>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org