I was tuning up on 160m, and the poor thing went dead. Won't power back up, either. Looks like I need to tear it down and find what mischief I did.

Finals? Or power supply? Suggestions from the symptoms?

73,
NG3P

Step 1: Out with the DVM.
73 de ZL2DEX

Based on what you have told us.? Beats us.

Likely finals.
First without a load assure yourself the power supply is ok.

The easy test for fried finals is pull the wire that power them
(and them only). I think it s brown.

Also hint if you are running more than 10W on any band, surprised
you should not be when heat gets them.

Allison

I'll check the finals. I have some spares, just in case.

I'd love to be able to control the power out on the uBitX without opening it up and turning a trimmer pot. If it had a control for output power, I'd use it. The stock machine, as I'm sure you've noticed, doesn't have a way to reduce the output power.

So it is what it is. Perhaps I was naive that it wouldn't blow up while trying to tune for a few seconds.

开云体育

Be very careful playing on 160m in the uBitX stock configuration. ?The PA easily puts out over 30watts with the second and 3rd harmonics to join the party as well. ?You should have a fuse in-line to stop the fets letting out the smoke. ?There is no ALC to tame the amp at low frequencies. ?Plus with the small heat sinks the fets go into melt down quickly.

That's a good suggestion, Adrian. I DO have a fuse in it. But perhaps not where you believe I should have one. I have one in the main power line. Where else do I need one? I fully expect the finals are now a crisp, tasty waffle from what you've just said. But that's ok, this is an experimenter's radio. I did an experiment and it poofed in my face, exactly what some experiments DO. But I also want to know what poofed, and why...and it'd be silly not to ask for advice from those who have had things go poof before.

Sorry I don't have much additional evidence to go by yet, but it had JUST happened. The heat sinks were a tad warm, and I smelled that nasty slightly fishy odor from a chip that has let out its magic smoke, so I expect the FETs are toast.

Come to think of it, though...the fuse. I think I'll check the fuse before I check the finals. Thank you for suggesting a fuse, because I DO have one, and hopefully that's all that went poof. I don't know why it didn't occur to me at the time.

73,
Gwen NG3P

The amplifier as is does not tolerate high SWR at power well.
With high power and high SWR the Mosfets get drain to gate
punch through.

Easy way to lower power, turn the power supply down as it will
work at 10V maybe lower.? Don't operate that way as the rest
of the radio may be unhappy.

The heat sinks are actually adequate if are can circulate freely.
Problem is often its a closed box and in that case heat rise can
be remarkable as it has no ware to go save to warm the closed
oven.? Vents and tiny fan can really help.

Allison

Maybe the fuse, its holder, dc cable maybe? I would check first the DC, than the rest.