|The AL-80B bandswitch, compared to the existing switch shaft.|
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 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.
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.|
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!