[R-390] CAPACITOR FIGHT

[David Wise]

I just had a brain-wave.  It might be possible to put a current limiter in series.  The Supertex LND150 is a 500V depletion-mode MOSFET that Mouser sells for $0.50.  Connect gate to source, and voila, drain current is limited to Idss, about 1mA.  Below that, it looks just like a 1k resistor (RdsOn).  The driving impedance is the previous tube's plate resistance, which should swamp a measly 1k.

If this works, you can LAUGH at C553!  Somebody try this.  Other projects are taking all my time right now.

Dave Wise
 
-----Original Message-----
From: John [mailto:jlkolb at jlkolb.cts.com] 
Sent: Tuesday, August 05, 2014 12:16 PM
To: David Wise; R-390 at mailman.qth.net
Subject: Re: [R-390] CAPACITOR FIGHT


Good point - Collins filter coil resistance is usually
in the 50 - 80 ohm region.  Any zener low enough to offer
protection would probably create IMD.

John


On 8/5/2014 9:47 AM, David Wise wrote:
> Down in the millivolts, I think.
>
> Correct me if I'm wrong, but I believe the resistance is low, which means that nothing can shunt away a current surge.
>
> Dave Wise
>
> -----Original Message-----
>
> What RF voltage is across the filter?  Anyone ever
> consider protective zener diodes?
>
> John
> KK6IL
>