Discussion in 'Amateur Radio Amplifiers' started by N4IJ, Jan 8, 2017.
All modern solid state devices are subject to ESD damage.
Odds are if you buy a transistor that has been around for a couple of decades it has been manufactured with modern processes which include small surface features, and will be just as supportable to ESD damage as more modern parts.
One other thing; that board needs to be where there is a little air flow, because of the power resistors on board.
Actually, I can guess pretty well that a device will fail in the middle of a live Rolling Stones broadcast... best to nip this stuff in the bud by following good ESD protocol. So far this has worked well for me.
"You can't always get what you want.
But, if you try real hard, you get what you neeeed!
And it's easy.
My fave is when their stage mics start picking up wild transmissions... Pierre (stage technical manager) and I found a fantastic spectrum analyzer to head that stuff off too. You haven't had fun until taxis start coming through loud n clear 30 minutes before show time and we're scrambling to pick clean channels on several dual diversity systems... Those were the days! (and I don't miss them)
I retired from that mess 15 years ago... Mr. Mom now.
Roger - copy
Electrostatic Discharge, electrostatic device...OH. lol
I read and comprehended Electrical Safe Distance --- As in OSHA, as in 4" per KV... Oh well, my utility inspection mentality pops out of retirement to haunt me sometimes. lol, prompting my reply above explaining how I want the end to come (when it's my time, of course).
In-hopes to rejoin the group discussion here on their plane, (the normal one this time):
I try not to ignore THAT ESD either, but yeah -- Not always as much as I should.
Given what the device is though, I think the level of handling protocol was met each time. At least, until the transistor was in-circuit. It is mounted to the chassis with insulators, and must be able to dissipate the heat it develops. This may be a partial issue, but the installation here should be enough to dissipate that heat properly.
Speaking of heat and getting rid of it; That on-board power resistor clearance thing is always something I try to take into account also, due to past experiences with flammable PCB substrates turning black and conductive underneath. On this amp, it was with the W7RY PCB and the soft-start module from Harbach. My only approach is to make sure power-handling capabilities are up to the application, then elevate them as much as physically possible and pray.
They aren't failing though.
Off -topic, I love that pic with the mallet on the desk above... Says a bunch, and me too... My motto = "If it don't fit, don't worry -- it will".
The air flow is a problem in both the TL-922 and the SB-220. The board needs to be on the bottom of the chassis and there is no air flow underside.
In my SB-220, there is airflow on the underside of the chassis. The tips of the cooling fan protrude below chassis in order to force air across the 3-500Z filament & grid pins.
OK - it is not the transistor at all. Strange but true - the input RJ1A relay had a bad coil. Nearly shorted (about 5 ohms) to the mounting case. I can wiggle the coil and
get it to not be shorted, but would never trust it to last. Actually the way the relay is made, I should not be able to wiggle the coil at all. Compared to another relay to
verify my finding. Doug N4IJ