Capacitor Primer needed!

[KX5JT]

If you replaced mica caps in the filter unit with ceramic that is at least part of the problem.  You really need mica caps back in place there. 

This statement has me thinking that a discussion on capacitors is really needed!  I have wondered many times, can I replace THIS type of capacitor with THAT type if the capacitance value is the same or nearly the same?  Why or why not?

Any takers?

[KA0HCP]

I suspect it relates to the inherent stability of the capacitor types at the particular operating frequency.   

[Steve - K4HX]

In receiver/low power circuits for sure. In transmitters, voltage and current handling become a consideration.

I suspect it relates to the inherent stability of the capacitor types at the particular operating frequency.   

[KX5JT]

In receiver/low power circuits for sure. In transmitters, voltage and current handling become a consideration.

I suspect it relates to the inherent stability of the capacitor types at the particular operating frequency.    

Steve, I certainly understand the ratings need to be observed and you can get away with overrating.  The question is more about TYPES and WHY certain types are a better choice in certain applications.

I can imagine tolerances also come into play.  But for instance, can electrolytics be substituted with non electrolytics for certain applications or do they always need electrolytics?

Other examples might be if an original circuit calls for a ceramic disk type, can I use an orange drop there if the values are similar?  These questions surely are asked by others too.  

Silver, mica, tantalum, electrolytics.... it can get confusing.

[KX5JT]

Any way a nice dissertation by someone knowledgeable on choosing the right capacitor types for application or replacment, restorations, etc might be a great candidate for the AM Handbook section.

[DMOD]

Well, we can start with this link:

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

[KX5JT]

That is a great link! Thanks!

[KM1H]

Other examples might be if an original circuit calls for a ceramic disk type, can I use an orange drop there if the values are similar?  These questions surely are asked by others too.

It should be the other way around as ceramic discs make much better RF bypasses. This is a popular discussion on receiver forums and a good example of the difference is the National HRO-60 which was in production from 1952-68 and went from paper, to mylar, to discs over those years. Those with factory discs have a lower 10M MDS than the mylar or rebuilt with OD's or the yellow film caps.

I use only discs in my own and most customer restorations for RF, IF and AGC circuits and 630V film in audio where the cost of suitable value and voltage discs is much more. A few customers request OD's so I bite my tongue and install those ugly lumps now made in China

In many circuits a leaky mica can be replaced with a NPO disc where the Q is not an issue such as in a LC circuit. In many LC circuits such as the lower frequencies and at IF the disc is fine and this is where many micas are become leaky. I use 1000V NPO discs on a regular basis for coupling and bypassing as well as where mentioned above. For homebrew I mix in both types as needed or whats on hand.

In some BA receivers a NPO disc in place of the existing mica or ceramic dogbone has improved HFO stability.

An electrolytic used for coupling in many circuits, especially SS, can be replaced with a film version as they were not available until recently at a low cost. It will be awhile yet before they will be used in HV power supplies.

Carl