Re: Failed IRF510 in BJ


David Wilcox
 

Curt,

That was one of my questions in this mornings email.

Yes, the BJ still works, in fact worked for a week before I discovered that it was hot.  Touched it while testing for reasons for the drifting problem.  Gets so hot that the middle leg is blue and I had wondered if I had left a soldering iron on while using it out of the case.

Another responder stated that it still gives reverse voltage protection if damaged by reverse voltage.  I had applied reversed voltage a few nights ago or maybe longer and praised the kit designer for protecting old or dumb farts like me.  

The rig still works, drifts intermittently, sometimes faster, sometimes slower.  During my first QSO it didn't drift enough to have to retune though, a nasty thought, because I would probably lose the contact while retuning.  Very touchy.  The shaft of the tuning pot wobbles, more than the shafts of the other supplied pots.  If I attach the tuning knob firmly against the faceplate it is much more stable and easier to tune.  Am going to apply some green felt behind the knob.  Remember that from the early days of radio, to help a knob tune smoothly and not scratch the cabinet?  

Dave K8WPE

On Feb 9, 2017, at 10:39 AM, wb8yyy@... [4sqrp] <4sqrp@...> wrote:

 

The IRF510 can take a large current from drain to source, and get very hot without damage -- I learned this the 'hot way' in connecting my Magic Box up to a tuna tin 2 type keying circuit (that has bias on its key interface) from a transmitter I had copied from N5IB (interesting this was the original BJ version!).  Just because the IRF510 got very hot does not mean it is dead -- this would likely gate damage to the gate to be dead in a normal 12 volt PA application.  I hope you tried to use the BJ after discovery of the hot device?  No need to add to the email chain if the device is dead, and is being replaced. 

everyone should keep building in spite of this kind of issues -- it is part of the adventure. 

73 Curt

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