The AM Forum

My AL-82  which I run as an AM Linear suffered a climactic event this afternoon (pilot error).

The end result is that the wiper that makes contact for 80 meters (one of my most used bands) apparently got real hot and malformed. You can see it in the picture which is actually 2 shots. In both pictures the 80-meter contact is on the top (you can see the carbon)

In the left picture, the switch is in the 80-meter position. In the right picture, you are looking at the same contact with the wiper in the 20-meter position. Note the damage to the wiper in the right shot.

The wiper has most meat left on it and seems to still be flexible. My hope is that I can clean it up in place and get it to work again. The amp survived fine and works on all other bands. On 80 there is no output so I am assuming there is no contact. Because of the coil interconnects it is hard to tell with an ohmmeter
 
Anyway, what is the best way to clean it? I was figuring some emery paper and Deoxit, and some gentle love with needle-nose pliers (with the wiper between contacts) when all done.

Hopefully, it is not a lost cause as the switch and components seem to be not available.

Thanks
Carl

Mistake

You have the right idea...looks like you might be able to clean that up..It might work too if the spring hasn't gone out of that contact..Good Luk...Steve

The good news is, you're on the right track.  I limped an sb220 bandswitch like that for years.  Finally went and bought a bunch of rotary switches that looked like the right stock.

Very slowly drilled the rivets out and removed each piece.  Rebuiot the entire switch that way.  Was very time consuming, but the sb220 switch is unobtainum now.

The better news is, Ameritron's is still in business and a new switch for you is a phone call away.  Again, time consuming, but available.

--Shane
KD6VXI

It would be a butcher job, but since 80m is your favorite band, just remove the band switch and hard wire for 80m. Alternatively, go the plug in coil route with added contacts in the plug to bridge in fixed capacitors on the lower bands.

I remember a few Globe King 500's that were wired for 10m permanently after the band switch was burned up from prolonged 10m AM QSO's.

Eliminating the band-switch can boost the efficiency, especially on the higher bands.

Jim
Wd5JKO

Carl,

Did you directly contact MFJ for support?  It looks like the AL82 is a current production item and MFJ is usually very good about making parts available.

Contact link:  https://mfjenterprises.com/pages/create-a-support-ticket

That wiper is going to be very questionable for further use given that burn/overheat.

And on edit:  They have some switches designed for amplifiers for sale in their catalog on P. 75, usually these switches are what are used in some of their products so take a look at those to see if the switch or at least the necessary parts are available from one:  https://mfjenterprises.com/pages/catalog?_pos=1&_sid=c9ac082f1&_ss=r

Rodger WQ9E

Thanks all,

Success!

I spent several hours carefully working on the contact and the wiper with a contact file, Deoxit Q tips, and prayers. The trickiest part occurred because, in the drama of the event, the wiper was bent away from the contact (probably by the heat).

By feeding thin alignment tools into the switch I was able to hold the switch between stops and also move the wiper away from the wafer. I could then gently bend it back towards the wafer so it would connect with some tension. The wiper material is very springy so this took a number of tries. I was also concerned that the metal might have been made brittle by the heat. Finally, because of the circuit set up, it was impossible to check my progress with an ohmmeter as it would always show a short to the coil.

I'm glad this worked as replacing the switch would not be an easy task. I'm not sure how Ameritron constructs this but it has to be a sub ssembly that is installed early on. It has numerous heavy-duty connections that are pretty much impossible to get to. Somehow the switch and inductors, made up of 3 different coils would have to be removed. I communicated with a ham who commercially repairs amps and he was really nice but not really interested in the project because of his knowledge of the design.

Rodger, the switch is indeed in their catalog, for $195.58, plus the previously mentioned challenges.

Let's see how it lasts..

Thanks all

Carl

Gud job Carl...a little clear thought and some manual dexterity and you are back in business...I hope it holds....Thanks for the description..

Hi Carl,

Sounds encouraging,  good luck   ...

AND,  if your work does not hold,  there is/was the chap who did a lot of 6 M conversions of Ameritron's large amps,  W1QJ.  On occasion he would offer complete Bandswitch assemblies  --  switch,  coils,  padders,  etc for about $200-ish.   You might want to check with him,  if needed:

http://www.qroking.com/About.html

FWIW,   73  GL,  Vic

Thank you Vic,
It is quite an assembly!
What happened to a single wafer switch with one long coil?