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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