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 <w9ac@arrl.net> 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 <topband-bounces@contesting.com> On Behalf Of VE6WZ_Steve
> Sent: Friday, September 13, 2019 2:55 PM
> To: topband <topband@contesting.com>
> 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
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