Topband: YCCC 9 Circle preamp failure

[VE6WZ Steve]

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 at 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 at contesting.com> On Behalf Of VE6WZ_Steve
> Sent: Friday, September 13, 2019 2:55 PM
> To: topband <topband at 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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