[Amps] Mica cap substitute \ alternative

[Peter Chadwick]

Rich said:
>Indeed, and frequency counts too since mica dielectric needs to be  
derated above 5MHz.<
What goes wrong with mica above 5MHz? it got used a lot in receiving and transmitting tubes, and as insulation in cavities at VHF and up where quite large RF currents were flowing. And as windows in tubes feeding wavguide, carrying appreciable power (like MW pulses). Is it just the wya mica capacitors are made?
73
Peter G3RZP