On the bench:

2011-February-10 - Success, Disaster

I have finished the RF deck for the 600W amplifier. Advice from the EMRFD Yahoo Group pointed me to the right lubricants to use when drilling or tapping copper. W4ZCB suggested Harveys thread cutting oil, 8 Oz bottle from Ace hardware for $4.49. I ordered that and the holes were then easily drilled and relatively easily tapped.

I tested the RF deck one evening after a long day at work. I connected up the power supply and set up an ammeter to measure the bias current. I slowly increased the bias voltage but the current barely moved, then the fuse blew in the power supply. I had a sinking feeling. It turned out that I was measuring the current in the actual bias circuit and not the current through the devices from the 60 Volt supply. There is no current into the FET through the gate. As I was increasing the bias voltage a large current flowed through the device and I destroyed it.

I gave up for the evening and have ordered some new FETs from ebay, not wanting to pay full price again here in the US. They are coming from Hong Kong, so could take some time.

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