Oh No

[W1MSG]

Had a bit of a scare the other night, yakking on 75m running about 1400 watts with the Commander HF-2500 and saw a flash out the corner of my eye and the amp kicked out. Reset it and my Grid current was CRAZY and as soon as I transmitted it spiked and kicked out.

Well now I am thinking a tube took a dump, not good as they are 5 to 6 hundred each for replacements. Opened up the top and was looking around for a possible blown diode which is common on Ameritrons when this happens, and found a blown 15a 250v fuse on the control board. Off to radio shack, and back in business. Not sure why the fuse blew but all is well now. Easiest fix I have ever had on an Amp.

 

[222DBFL]

Was it hot when you touched it? Maybe it's not making good contact. Give the connections on the board a good cleaning. Might have been an old fuse as well and just happened to meet its end.

 

[W1MSG]

Was it hot when you touched it? Maybe it's not making good contact. Give the connections on the board a good cleaning. Might have been an old fuse as well and just happened to meet its end.

My guess is its just old and met its end, the connections are clean and the fuse snaps in very securely. They havent made these amps in quite a while so it could just be showing its age..

 

[Shockwave]

That fuse has to be for the B+ supply and the way it looks, it opened under a heavy current load. It's possible it was slightly out of tune or an arc occurred in the output stage that took the fuse out. The high grid current you saw when you reset was the result of applying drive with no B+ due to the open fuse. In this case the grid is dissipating the full drive power in the absence of high voltage. Good thing for you the amp is protected against that and tripped right back out.

That's what you get when you buy an expensive amplifier that is well designed. The pleasure of replacing a $1 fuse in a fault situation rather than a $600 tube.

 

[W1MSG]

The commander has some great safety kick out features, I just dont want to have to recap it as you have to disassemble the entire amp. A rather poor design in that aspect.

 

[Shockwave]

In order to fit all those nice features inside a reasonably sized cabinet, sometime you have to stack things in layers. I wouldn't call it a poor design yet unless the caps they used failed prematurely.

 

[W1MSG]

In order to fit all those nice features inside a reasonably sized cabinet, sometime you have to stack things in layers. I wouldn't call it a poor design yet unless the caps they used failed prematurely.

True, but caps do need to be replaced. The company was suppose to start back up but I guess it fell through and the new design for the cabinet had a trap door in the bottom for access. If I ever have to dig that deep into this one I will most likely have a door cut in the bottom for access. But of course this thing will most likely out live me, or at least another 25 years or so.