Saturday, December 21, 2019

Replacing the AL-80A Bandswitch

The AL-80B bandswitch, compared to the existing switch shaft.
With my wallet being $115 lighter, the AL-80B bandswitch arrived within a week. Now, it isn't the same as the original AL-80A bandswitch.

There are two key differences. First, as you can see from the picture, the shaft layout is different. In the original AL-80A bandswitch has the input network switch wafter in front of the bandswitch, whereas the AL-80B has it behind the bandswitch.

This means you can't just replace the AL-80A switch with the AL-80B switch. The best you can do is to unstack the wafers and put them on the original AL-80A switch shaft.

AL-80B switch with AL-80A wafers.
The second difference has to do with the switch wafers. Electrically, they are identical. The AL-80B switch has the 160m padder cap and the Pi-L network wafers reverse. Since we're going to re-stack the wafers anyway, this doesn't matter.

The Pi-L wafer is positioned differently. The contacts are two positions counter clockwise (as viewed from the front of the shaft) from the AL-80A. This means that a bit of re-wiring is necessary to make the connections.

Wafer-less switch.
Removing the switch wafers isn't a big deal, since I have done this earlier. The rear wafer comes off with all the coils attached, and the padding caps unscrewed, there being only one wire that needs to be unsoldered, and it slips off. The middle wafer has a similar wire to be unsoldered, and it comes off as well. The front wafer has one wire to the padder cap, and it comes off as well.

With all the wafers off, the new switch wafers are stacked on. Because the Pi-L wafer has contacts rotated two positions, they are a little harder to access between the switch and the loading capacitor.

New wafers in place.
Once all the wafters are on and screwed down, the next step is to re-solder all of the connections. I took lots of pictures before unsoldering the old wafers, so I had a pretty good idea of what goes where.

Front switch wafer anchors the coax shield, and adds the 160m padder cap. The Pi-L switch wafer was the only one that gave me trouble. Since the contacts are rotated from the original, this required a bit of extra wire to make the required connections. The rear switch wafter has five connections tot he coil assembly. It took a bit of work to unsolder. This sort of thing is best not rushed and done with great care, to avoid damaging the coils. Everything goes in the same place on this last switch wafer, which was easy once I got all the coil wires into the right positions in the narrow switch contact lugs.
The finished product. Reassembled with new switch wafers.

Sounds easy, eh? But realistically, it was nearly three hours on the workbench.

Moved it back to the operating desk and tested for full output into a dummy load on all bands. No problem on 160, 80, 40, 20, 15 and 10m.

For 17m and 12m, I proceeded more cautiously. The AL-80A is designed to operate on 12m using the 10m switch position. It works on 17m using the 20m switch position. But it has often been on 17 or 12m that I've had the most issues with arcing in the PA circuit.

For this reason, I've decided to reduce drive to about 30 watts for 17 and 12m. It's a little less output power, but also less of a chance of burning up a $115 bandswitch.

With the testing done, it was time to button up the amp. Took me about 20 minutes to find 10 of the 13 screws that hold the cabinet top on. I had removed them a year and a half before, but finally found them in a neat pile on the workbench.

The AL-80A is back up and running on all bands!

Friday, December 20, 2019

Digging back into the AL-80A....

Front switch wafer - showing contacts burned
completely away.
Back in July of 2018, I was chasing the KH1/KH7Z expedition on 17m, and the AL-80A stopped producing any output. I dug into enough to find that the Pi-L output switch contacts had arced and burned. So, I jumpered the switch so the amp was only usable on 40m and above. And it has worked OK since then - but not on 80 or 160m.

It's way past time to fix this, so I recently got started. I figured that I just needed to replace a switch contact or two like I've done before.

Back side front switch wafer showing more
contacts completely burned away.
Once I got the lid off and removed the switch wafers, well, the photographs tell the sad story.

Middle switch wafer. You can see my jumper
between the to contacts on right. There was not
enough material on the switch wedge to make
contact with the 40m contact.
Replacing the contacts won't be enough. Plenty of the switch wiper was gone on the Pi-L (middle) switch wafer -- especially the corner that used to short out the Pi-L coil on 40m. And the 160m padder capacitor (front) switch wafer isn't any better.

No, this means I'll have to replace the switch entirely. I've ordered one from Ameritron, with shipping it came to $115! This is the AL-80B switch, which is similar, but not identical.

Saturday, December 14, 2019

Sorry, I've been a bad blogger.

I just noticed that I had a number of comments awaiting moderation and I just published them all. Sorry about that folks.

Used to be Blogger would send me an email when I had comments, and I could moderate them then. Apparently, they stopped doing that about a year and a half ago.

So, if you left me a comment on one of my articles, it's published now. And I may have even answered it....

I'll try to keep on top of this in the future.