Ameritron AL-572 Burning Smell

[K8AXW]

So, what is the "pillar?"    It must be carrying power or it wouldn't heat up.  What generates heat in something is either the conductor is too small or the connections of the conductor is poor.

If the bottom of this pillar connects to a foil trace on the PCB, how about a terminal lug under the pillar with a jumper from the terminal lug to the trace?  Make sure all screws are tight.

[HS0ZJU]

So, what is the "pillar?"    It must be carrying power or it wouldn't heat up.  What generates heat in something is either the conductor is too small or the connections of the conductor is poor.

If the bottom of this pillar connects to a foil trace on the PCB, how about a terminal lug under the pillar with a jumper from the terminal lug to the trace?  Make sure all screws are tight.

I can.surely beef up the.connections. My.concern is it just bad design or is there a underlying problem causing too much current draw?

[K8AXW]

I'd put money on a bad connection.  I'd simply beef it up using flat washers for support on the burnt PCB and take the power from the pillar with a solder lug and jumper wire.  Make sure all is good a tight.  (The solder lug is internal toothed so no lock washer is needed.

[W8JI]

I have located the problem please see photos. I re-soldered and tightened the connection but the pillar is still heating up at bottom connection. What would be a better approach to repair?

http://i254.photobucket.com/albums/hh88/funbiz99/al572%20eham/P1040136.jpg

That spacer carries current to the loading capacitor. Make sure that spacer is tight at the board end. To tighten it, remove the screw at the top and tighten the spacer by turning it snugly with pliers. The screw is fairly strong metal.  If the board has been damaged by arcing or heat, do what K8AXW suggests.

73 Tom

[HS0ZJU]

@k8axw

I did the repair as you suggested and more. At this point it is no longer burning between the screw/pcb/spacer.  The pillar/spacer still gets very hot if tuning more then 10 seconds in cw. For me it is not a issue as i never need ten seconds key down.

73 marc hs0zju/k4hyz

[W8JI]

@k8axw

I did the repair as you suggested and more. At this point it is no longer burning between the screw/pcb/spacer.  The pillar/spacer still gets very hot if tuning more then 10 seconds in cw. For me it is not a issue as i never need ten seconds key down.

73 marc hs0zju/k4hyz

If it gets hot, a foil has been damaged on the top or bottom or the washer is high resistance (perhaps anodized or perhaps corroded from humidity or heat).

The spacer connects both on the top foil and bottom foil, which are wide for RF current.

Unfortunately you have to drop the front panel forward and slide the tank assembly out to redo much more. If it gets hot that fast, there is still a connection issue there.

Another faster fix might be to install a wide copper or brass strip from the outside stator connection stud of the loading capacitor to the band switch common terminal. That would divert some current to another path.

I would do something, because there obviously is still a problem there.

[HS0ZJU]

***Update***

I soldered two crimp lug terminals to the foil on each side of the pcb. This should give good continuity to the screw head and the spacer connection. This seems  to be working as the connection is no longer burning.

After about 10 days of testing a new problem has cropped up. The plate tuning capacitor is arcing? I did not think it was possible but am 99.9% sure that it is arcing there...Any ideas? 

73 marc hs0zju/k4hyz

 

[K8AXW]

TUNE cap burned or deformed from a previous arc

Improper tuning

Bad tube(s)

Use dummy load instead of an antenna

Even though you've been working on the amp, please make sure it's unplugged and the HV has been shorted to ground.

Look at the TUNE cap and see if there are any burned spots (look at the edges of the plates - that's where they arc) or bulges of the plates.  If you find any problems they can be repaired but it is a very time consuming process requiring a great deal of care.  Sometimes it's simply best to replace the cap.

Replicating the arcing situation in a dark room helps.  This arcing cannot be tolerated very long or you will indeed have major problems.