Found the subject very appealing. It moved me to read about Hartley, Colpitts and Clapp oscillators. I see this as a challenge to do something that works.
My recent Colpitts is the first LC oscillator I've built in 50 years. The very first was for my AM xmtr in the 80 and 40 m band; say , zero experience. Surely mine has unknown flaws while the output is a not so bad sinusoid.
When you wind the air coil, stabilize it with hot glue or or epoxy once you tune the frequency. Or use the tunable inductors with the slug that can be turned with a non-magnetic screwdriver (diddle stick). A standard air coil will be easier to change the fluid or material to measure permittivity.
When you wind the air coil, stabilize it with hot glue or or epoxy once you tune the frequency. Or use the tunable inductors with the slug that can be turned with a non-magnetic screwdriver (diddle stick). A standard air coil will be easier to change the fluid or material to measure permittivity.
When I decided to build the Colpitts, three weeks ago, I recalled a small trove of coils and variable caps that I got also 50 years ago. They are four "plug and play" modules for 60 or 70yo Ericsson (or maybe GE) transmitters that I had the chance to see still in service in a radio station.
Huge wardrobes (on their wheels) you had to pull for plugging them to change the frequency band.
Your post also reminded me of some coils forms that should be around here with tuning slug. Have to look where are they.