Re: Something has been blown

Jerry Gaffke

If the IRF510's still draw some current through PA-PWR during transmit,
and that current changes when you adjust the gate bias with RV2 and RV3
(adjust this very carefully, as it quickly goes to hundreds of mA)
then the IRF510's are probably just fine.

Regarding cheap IRF510's on ebay, you might read this old thread:
They cost $1 on mouser for singles, below $0.50 if you buy lots, and you know who made it.
I don't see much point in buying on ebay.

As Arv says, make sure you have a good 50 ohm dummy load when testing.
Perhaps get four Xicon 200 ohm 3W metal film resistors (mouser 283-200-RC)
when buying the spare IRF510's.

Jerry, KE7ER

On Thu, Jan 25, 2018 at 07:31 pm, Arv Evans wrote:
Since there is no short with the IRF-510 devices in place but not connected to the chassis, it is 
possible that the antenna was disconnected, shorted, or some other anomaly.  Unfortunately
MOSFETs used as RF power amplifiers tend to self-destruct if the load is not of proper
impedance.  Too low an impedance and they will overheat, and too high an impedance and
they will go into oscillation and destroy themselves with high current. 

As Bernie KC9SGV has suggested replacement devices are relatively inexpensive from Ebay
vendors.  Some will probably raise the issue of Ebay sourced parts being less than perfect
but I have been using Ebay sourced IRF-510's for over 10 years with no problems. 

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