[Amps] MLA-2500 Bandswitch Arc

[Tom W8JI]

> As I've been working on my Dad's MLA-2500 (not the B 
> model), I've
> noticed that at some point in time, there must have been 
> an arc
> between the 10 m coil tap contact and the adjacent ground 
> contact.
> For those of you familiar with the amp, this is on the 
> front-most
> wafer. The contacts are otherwise perfectly intact: I see 
> no other
> evidence of overheating and the solder looks fine save for 
> evidence
> of the arc. I have no idea what the conditions were that 
> caused the
> arc and my Dad has no recollection of it. Neither of us 
> can even
> think of when the amp may have been used on 10 m.

That tap has the highest voltage when the amp is on the 
lowest frequency bands. It has the lowest voltage when on 
ten meters.

So if you are looking for an arcing failure to another 
contact of the ten meter tap while the amp is on ten, you 
are looking for a failure when it is least likely....not 
most likely.

It is most likely on 160 and 80, least likely to arc on ten. 
The voltage to ground increases as more tank coil is 
selected.


To clean it up you can scrape the area with a non-metallic 
tool. I use fiberglass soaked in a very light hydrocarbon. 
You will only make matters worse if you deposit metal on the 
ceramic near that contact.

73 Tom