Hi Roger,
I'm looking at the W2 kilowatt sensor schematic and scratching my head
trying to figure out how that could have happened. There are 49.9k
resistors in series with all the op amp inputs, so there would have to
be hundreds of volts coming out of the detectors to damage the devices.
Plus the fact that all 4 op amps (actually two dual op amps) were
destroyed argues against that as well.
I would suspect the 5V op-amp power supply. Perhaps there was a failure
in the W2 power supply or maybe a spike on the supply. A large voltage
transient causing a current spike in the sensor cable might do it,
although it is hard to imagine 50W at 475 kHz doing that.
Alan N1AL
On 05/12/2015 11:21 PM, Roger Crofts wrote:
I made a rare QSO on 630 metres the other day. My W2 wattmeter was
in-line between the 630m transmitter and the 630m tuner. I was not
using the W2, because my 630m transmitter has its own internal SWR
meter. When I returned to normal HF operation, I noticed the W2 was
not working. I discovered all four unity gain op-amps in the W2
directional coupler were destroyed. I replaced the op-amps and the W2
operated normally again. The W2 wattmeter is not intended to operate
below 1.8 MHz, but it does have a 2KW rating, so one could be
forgiven for assuming it could handle 50 watts at 475 KHz. Next time
I operate on 630 metres, I will by-pass the W2. Roger, VK4YB
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