[Amps] Fwd: Re: 4-400A Input impedance

[Bill Fuqua]

>Not only that, you must operate class C and the screen grid must be 
>modulated along with the plate.
>
>73
>Bill wa4lav
>
>
>
>At 08:47 AM 1/18/2006 -0800, you wrote:
>> >Anybody know what the input impedance is for a pair of 4-400A's operating
>> >plate modulated class Connected in parallel?  Is 50 ohms close?
>>
>>Since you are talking about 50 ohms, you must be considering Cathode drive.
>>Since the input is part of the output with cathode drive, it cannot be used
>>with plate modulation - unless the driver is plate modulated also.  It is
>>rarely done.
>>
>>Perhaps you are plate modulating the driver and not the final amp.  If the
>>4-400A is used with all the grids grounded, I would guess about 70 ohms
>>impedance.
>>
>>If you are plate modulating the final amp, it is easiest to drive the grid
>>and hang a resistor on the grid to determine the drive impedance.
>>
>>Colin  K7FM
>>
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