[AMRadio] HV Capacitor question


Jim Candela jcandela at prodigy.net
Tue Jul 18 14:24:45 EDT 2017


"Take a look at Notes 1, 2, and 3"
Some good reading for sure. On the Central Electronics 20A the 6BA7 mixer B+ bypass cap (C73) is usually a .005uf Silver Mica. Change that out with a ceramic Z5U, and the gain drops a bunch, especially on 40m.The mixer uses a high Q tuned circuit, and the RF circulating current passes through that cap. I once tried an equal value polypropylene, and the gain was too high!! I had to put about 2 ohms in series with it to make the circuit behave. Those polypropylene's are low ESR caps with good high frequency capability.
Back to my electrostatic clamp controller, I just ordered some poly caps from Mouser. The value is .033uf @ 3KV.  Two of those should replace six of the .01uf ceramic Z5U's in there before (2 groups of 3).
My thinking is that the "bad" Z5U's that can generate up to 1 volt into 10 meg-ohm when hot just have a infinite number of series R-C networks within, and to deplete the stored charge, perhaps I can short them out and put them in an oven at 100 Celsius for several hours. Might be a fun experiment. Would also like to put a microamp meter across the cap, heat it, and see if I can achieve a reading above zero ua...Might find that I have a new form of power for a QRP rig!!  :-)

Thanks for the comments guys.
JimWd5JKO

      From: sr2000 k9axn <hallicrafterssr2000 at k9axn.com>
 To: Jim Candela <jcandela at prodigy.net>; AMRadio at mailman.qth.net 
 Sent: Monday, July 17, 2017 11:37 AM
 Subject: Re: [AMRadio] HV Capacitor question
   
Jim,

Take a look at Notes 1, 2, and 3

https://www.k9axn.com/_mgxroot/page_10835.html

Kindest regards Jim K9AXN


   


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This page last updated 17 Nov 2017.