>
>> 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
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|