Why Door knobs?

[abstruse1]

I continue to fool with CW multipliers, with not much success.  This question occurred to me: why do people use doorknob caps when ceramic caps (the common, blue ones) with the same voltage and capacitance ratings are much less expensive?  The more epensive doorknob type must have some benefits.

Thanx.

[klugesmith]

Same voltage and capacitance ratings, OK.
How about RF current rating?  ESR and ESL? Dielectric loss properties? 
Temperature and voltage coefficients of capacitance?

Details can be found in component datasheets, product family documents, and by more Internet searching.

[Mads Barnkob]

Door knob capacitors is constructed for very low tolerances, low temperature drift and to be sturdy and stable in RF applications, because they are often used in tuned circuits that needs to hold its frequency despite temperature changes.

Blue disc ceramic capacitors might have the same ratings in capacitance and voltage, but are much less stable and capacitance can vary up to 20% with temperature changes in its specified range.

Thermal mass in pulse applications is also a important factor. The door knob will have more mass to help it dissipate conduction losses, the smaller ceramic disc will heat up faster.

For a experimental voltage multiplier with little intermittent use, ceramic capacitors will do fine. For a sturdy voltage multiplier in 24/7 operation, door knobs

[abstruse1]

Thanx, guys.