Hi
I have a 5 tube trf homebrew radio
one of the parts on it says "calibrating condenser" and on the next line reads .0002. Is this just a .0002 mf capacitor? Should I replace it? It does not look like the typical wax/paper or mica capacitor. Any help would be appreciated.

Josh

Josh, I'm not familiar with the term "calibrating condenser." (TRFs often have compensating caps and neutralizing caps, but I would expect neither would be 200pF.) Can you tell us where this is wired in the circuit?

Is it, by chance, a variable trimmer cap?

I wouldn't yank it out until you can confirm what it is and its function.

A calibrating condenser would probably serve the function that the trimmer and padder condensers serve in commercial radios. Both would be the same, then. A padder condenser goes in series with either the tuning condenser or the associated coil. Changing its capacitance affects the low end of the dial the most. A trimmer would be in parallel with the tuning condenser and its associated coil. Adjusting this would affect the high end of the dial the most. Both will affect station spacing all over the dial to some degree.

If your TRF has one of these condensers for each stage, then all must be adjusted so that all of the stages tune as much alike as possible (if they are all linked together mechanically). If not, the stages will be out of sync with eachother. Narrow selective tuning won't be possible. Sensitivity will suffer wherever the stages are out of sync (not all tuning in exactly the same frequency).

Thomas