I have a QMX 60-15m kit and I made a mistake that cost me capacitor C521, an 82pF ceramic capacitor (82J/820). I have a bundle of ceramic capacitors in my drawer, including 82pF ones. Are there any special considerations I should take into account when selecting a replacement or will any 82pF ceramic capacitor do?

Alex

These capacitors are NP0 50V, most likely Vishay.

72 de Russ, va3rr

Apologies. I neglected to mention 2.5mm lead spacing.

You need to watch out for the required voltage rating (If on the capacitor this will be specified as DC and the AC RMS value (if the maker bothered to specify one) may only be half of that).? In higher power RF applications low losses become more important?

Also 'ceramic' capacitors are available in a whole variety of materials,? some give a high capacitance for small size but that capacitance is ever-changing with temperature, applied voltage etc.? ? Others sing if the application has audio frequency pulses or ripple.? These types are only suitable for low size, low cost decoupling but I prefer them in? the rubbish bin?

Other materials? are more stable and of those some are even suitable for RF tuned circuits -but at a size and price cost

When you buy capacitors get them from reputable suppliers, keep them in part number marked packs and save the manufacturers data sheet

I'm unable to tell you what is already ' in your drawer' from here though

On Tue, Jul 9, 2024 at 09:24 AM, Bruce Akhurst wrote:

Also 'ceramic' capacitors are available in a whole variety of materials,? some give a high capacitance for small size but that capacitance is ever-changing with temperature, applied voltage etc.? ? Others sing if the application has audio frequency pulses or ripple.?

NP0/C0G capacitors have none of these vices.? There is another level of performance available from porcelain dielectric capacitors, exemplified by the venerable ATC100A series, now produced by Kyocera/AVX, but they are specialty microwave stuff.

X7R, X5R, Z5U and similarly-designated are the ones to avoid.
?
The issues are due to the high-K (dielectric constant) materials used to obtain large capacitances in tiny volumes, which also tend to exhibit electrostriction and/or magnetostriction and have large coefficients of capacitance vs voltage and temperature, which accounts for the "singing" and also intermodulation due to the capacitance changes, in audio circuits.? They can also be microphonic due to piezoelectric effects.??
They have their places where bulk capacitance is needed, but not in tuned or RF circuits.??
73, Don N2VGU

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