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[AMPS] 4CX1000A advice??

To: <>
Subject: [AMPS] 4CX1000A advice??
From: (Rich Measures)
Date: Sun, 15 Mar 98 08:05:46 -0800
>km1h @ wrote:
>>On Sat, 14 Mar 98 05:44:02 -0800 Rich Measures <> writes:
>>One of the "no hassle" untuned input circuits floating 
>>>about recommends putting an inductor in series with the grid 
>>>R to improve the 12m and 10m input SWR.  Doing so is an invitation to vhf 
>>  If Emtron, QRO, and Alpha do not use such a circuit,  Good. 
>>> .   However, one does not know until one sees the circuit. 
>>I do not know what they or Alpha use.
>The 91B "absorbs" the input capacitance of the 4CX800As by making it act
>as C2 in a pi-network. The tube input capacitance is about 100pF total,
>and the fixed capacitors used for C1 are about the same value. Thus the
>transceiver sees a 1:1 impedance transformation into the 50-ohm
>terminating resistor. 
>At all HF/VHF frequencies, the grids see the 50-ohm resistor connected
>directly to ground.
If the grids are connected directly to ground, how it it possible to 
deliver grid bias potential to the grids? .  No neutralization?  .  Eimac 
recommends neutralization.  


R. L. Measures, 805-386-3734, AG6K   

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