[AMPS] Another Stupid Question

[2]

>
>> What determines the capacitance value for a plate-blocking capacitor? 
>> By this I mean the capacitor (usually a doorknob cap) between the
>> plate choke and anode connection, and the start of the tank circuit /
>> pi network.
>
>Mostly it seems people just guess at what to use, and never think 
>about why a certain value is required. Most of the sizes used are 
>actually just plain silly..being far too big in capacitance..and too 
>low in current rating.  
>
>Technically, all the capacitor has to do is effect the impedance of 
>the tube anode a minimal amount.
>
>If the anode load impedance is 3000 ohms (you have to include the 
>choke, and do this on the lowest frequency), a 300 ohm reactance 
>blocking capacitor would have minimal effect on the system. 
>
>That means you only need  about 300pF blocking C for 160 
>meters, if the anode system's operating impedance is 3000 ohms.
>
>I remember laughing at a friend of mine who stuck a 100pF 
>blocking capacitor (by mistake) in his 3-500Z amplifier for 160. 
>When he changed the part to 1000pF, nothing happened except 
>the tuning capacitor slightly changed position. Efficiency and power 
>out remained the same.
>
//  Amen, Mr. Rauch,  Another Ham radio old wives' tale bites the dust.  

-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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