[TowerTalk] YCCC 9 circle preamp failure test

[jimlux]

On 9/24/19 11:09 AM, VE6WZ_Steve wrote:
> Yesterday I decided to measure the actual voltage at base of my short HI-Z verticals while I transmitted on the TX array.
> 
> Since I first posted about the coupling capacitor failures in these units, I have received private emails form 4 others with the same problem.
> 
> My question is what has caused these failures? Is it a lightning event,  is it high-potential wind static on the vertical elements or is it from TX RF overload.
> 
> TX overload seemed possible at my location because my array is less that 100’ from the TX antenna.  I built a diode detector probe and in the field measured the actual voltage when TX.  The results indicate at most I see 50 v at the pre-amp.  The coupling caps are 63v rated units.  This would indicate that RF overload is not the cause, but I would really like thoughts and opinions from others.
> I have redesigned the amps to include a relay to short out the antenna when not powered up, so I feel I am protected from any cause.
> 
> Here is a link to a YouTube video that shows the test set-up and the actual measurements I made in the field.  I also talk about using gas discharge tubes as a remedy.
> 
> https://youtu.be/TmM_YnLob68 <https://youtu.be/TmM_YnLob68>
> 

Is the schematic for your preamps published somewhere?

Is your diode probe high Z or 50 ohm?