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Re: Topband: YCCC 9 Circle preamp failure

To: Paul Christensen <w9ac@arrl.net>
Subject: Re: Topband: YCCC 9 Circle preamp failure
From: VE6WZ Steve <ve6wz@shaw.ca>
Date: Fri, 13 Sep 2019 15:37:19 -0600 (MDT)
List-post: <mailto:topband@contesting.com>
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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