[AMPS] Feedback path 3-500Z

[measures]

>
>> 50 microhenries of plate choke with the shunt plate tuning capacitor, and
>> the capacity of the loading capacitor in parallel (as it is connected
>> through the long lead that is the tank coil), bearing in mind that if the
>> load is not a resistor, but an antenna, at low frequencies, it will tend
>> to look like a high impedance.
>> 
>> We are not talking about 'choke resonance' where the choke with its
>> inherent distributed parasitic componets of reactance resonates, but of
>> choke resonance where the choke is tuned by the other discrete components
>> in the circuit.
>
>The units I measured had a parallel anode resonance (with the 
>output port terminated) of over 10,000 ohms somewhat below the 
>AM BC band.
>
Wolf!, wolf!

>The circuit involves the blocking capacitor, the plate choke, the 
>shunting capacitance below the plate choke, and the additional 
>choke in series with the power supply lead. The power supply 
>looks like a near-perfect short at LF because of the electrolytics 
>and other components. The reactance of the blocking cap parallel 
>tuned the complex network of the two chokes in series, with a 
>capacitor shunting the mid-point between the two chokes. 
>
any port in a storm.  

>By adding series inductance to the output port, the amps I tested 
>would take right off at VLF.
>
>Loading the grid chokes with a 1000 ohm resistor stopped the 
>problems, but the best bet is to remove the parallel resonant circuit 
>on the grid.
>
>Placing unloaded chokes in grid leads is very poor engineering.
>
> 
When driven, a SB-220's grid potential is typically under 6v and the grid 
current is c. 170mA.  Thus, the grid looks like 30-something ohms.  .  In 
the Rauchian world,  grid R is infinite.  

cheers

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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