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

[Steven Katz]

Wow.

This capacitor doesn't provide power to anything, and the MFJ-989C doesn't have an S meter.

It would not be rated "3kW," as capacitors aren't rated that way at all.

It's actually a low voltage variable capacitor used for compensation to help SWR meter accuracy.   Making it adjustable is a good idea.

It's a very small capacitor on the SWR bridge circuit board and one of these shown on this page might be similar:  https://www.electronicsurplus.com/capacitors/variable-capacitor    Even at 1500W applied RF power to the tuner, the voltage across that capacitor will never be more than about 100V assuming the tuner is adjusted for a match so the XMTR side of the bridge will look like about 50 Ohms.

If you call MFJ they probably stock this component and it might be easy to just buy a direct replacement.

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of A Lawrence Fibich
Sent: Saturday, September 24, 2022 11:24 AM
To: amps at contesting.com
Subject: [Amps] suggestion/recommendation wanted for a 'tunable' 15 pf capacitor on MFJ 989C tuner

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 _______________________________________________
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