[TenTec] Fw: Need Caps for Titan II Please

[Jim Brown]

On 4/11/2013 2:37 PM, Robert Mcgraw wrote:
> BINGO on difference!  Do check the RF current rating for the caps of
> choice.  It is not the voltage that frys them, it is the heating from RF
> current that makes them go pop!

Yep."Equivalent Series Resistance" (ESR) is a very important 
specification for a capacitor that carries significant AC current, and 
in a capacitor anywhere in that output stage is going carry a lot of 
current.  ESR is exactly what it says -- an imaginary resistor in series 
with the capacitor that, when carrying the current that is present, 
accurately predicts the power lost (and heat produced) in the capacitor.

One of the reasons those caps are cheap may be that their ESR is high.

We still have a nice, old-fashioned electronic surplus store in Silicon 
Valley that's a big warehouse full of all sorts of electronic 
components. When I first moved here, I needed caps to rebuild my Ten Tec 
tuners, and to use in antenna matching networks. I bought a good 
selection of HV caps. No specs are listed, of course, only voltage 
ratings and cap values, but at average costs of 5-10 cents on the 
dollar, you can afford to stock up and smoke test them to find the ones 
that can handle current.

I stuck them in series with the feedpoint of my 160M vertical, ran legal 
limit to it for a few minutes, then went outside to check for heat (and 
smoke).  It didn't take long to find the bad ones. :)

73, Jim K9YC