Paul is absolutely correct. The op-amp is a configured as non-inverting. I incorrectly “assumed” it was wired to invert simply because all of the pre-amps show the same 180 phase shift.
Steve From Babcocks iPhone > On Sep 13, 2019, at 1:56 PM, Paul Christensen <[email protected]> wrote: > > Steve, > > I recently ran into an identical problem with an Alpha 89 amplifier. A pair > of 0.01 uF/100V caps had failed on the plate choke clapper arm relay. The > caps are used on the relay coil as an RF bypass to ground. In time, RF caused > the caps to become leaky. With 1KW RF applied on some bands, the clapper > relay would open and close by itself. The caps are now replaced with leaded > MLCC types rated for 1KV. > > BTW, the op-amp circuit in your video is non-inverting, not inverting. If an > inversion is taking place, it's occurring due to the winding direction of the > 1:1 transformer's secondary with respect to the primary. > > Paul, W9AC > > > > -----Original Message----- > From: Topband <[email protected]> On Behalf Of VE6WZ_Steve > Sent: Friday, September 13, 2019 2:55 PM > To: topband <[email protected]> > Subject: Topband: YCCC 9 Circle preamp failure > > After 2.5 years of flawless operation, earlier this summer my YCCC 9 circle > rx array started to develop some strange inter-mod noise, and random junk > showed up on 160m when using the array. > > I isolated the problem to be the .1 uF coupling capacitors on the input of > the amps. This happened on 4 of the 9 amplifiers. > The most likely cause is from TX overload because this array is only about > 125’ from my parasitic TX array. (the TX antenna is detuned when on RX and > presents no issue on receive). > At first I suspected a nearby lightning strike, but the 4 failed amps happen > to be the closest to the TX array, nothing else in the amp was damaged, and > there was no other evidence of a lightning event at the station. > > Here is a link to a YouTube video I made showing how I isolated the problem. > Using my scope I show how the output from the damaged amp has significant > phase and amplitude distortion, and using the multimeter the failed caps are > evaluated. > > https://youtu.be/t6oux3MStDw <https://youtu.be/t6oux3MStDw> > > If you have one of these arrays, I show how it is very easy to test the > pre-amps in the field using your multi-meter to confirm if a similar fate has > occurred in your system. > > 73, de steve ve6w > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector > > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
