Anode inductor - why? - RF Cafe Forums
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Post subject: Anode inductor - why? Posted: Wed Jul 12, 2006 9:36 am
Joined: Fri May 19, 2006 5:01 am
I am still working on my digital tube radio, and came across this setup in the schematic of a Sherwood 3000 radio:
Both tubes are limiter stages. The IF is 10.7MHz. I estimated the value of the inductor based on size and core.
What does the anode inductor do? The thing that really puzzles me is that it is tunable (I have the radio sitting next to me). There is a turnable ferrite slug in there. What could it possibly be tuned WITH?
Post subject: anode inductor - whyPosted: Thu Jul 13, 2006 6:13 am
Joined: Fri Feb 17, 2006 12:07 pm
Location: London UK
It is to resonate roughly at 10.7MHz with the combination of stray capacitance around the tube base plus the anode to suppressor capacitance of the EF89 first stage plus the input capacitance of the following stage. Note the latter will be magnified somewhat by Miller Effect
Since many of these values can only be approximately estimated, the inductor is usually adjustable