[Amps] suggestion/recommendation wanted for a 'tunable' 15 pf capacitor on MFJ 989C tuner

[A Lawrence Fibich]

There is a tunable ceramic Capacitor listed as 15 pf in these tuners. They are on the RF output and provide power for the S Meter. Capacitors in the area are rated as 3 KW - I have been unable to find a 'tunable' micro size and wonder if simply using a 15pf  3 KW capacitor would work - don't know why a 'tunable' is used and can't find one and unknown what voltage would work.  No response from MFJ.  ? Any suggestions appreciated.  Apparently with age ? and tuning up an amp destroyed this part. Larry FSacramento CA areaW6EF