MB40L Mod?

[KA8WTK]

All,
  I just got an amplifier deck built to the plans from the 1953 ARRL Handbook page 202 (except for the plate coil mod in the article). The unit is built for a 4-250, but has a 4-125 in it now. It has a 4-400 in its future.
  The deck uses the MB40L input circuit, but with a twist. It has a switch in it to tap the input coil of the MB40L. The switch is marked 80-40 and 20-10. I assume this is to maintain a better match to the driver.
  Has anyone ever seen documentation for this? I can't seem to find any on the net.

Thanks,
            Bill KA8WTK

[Opcom]

http://amfone.net/Amforum/index.php?topic=42069.0

The tap is an attempt to vary the turns on the link because for the higher bands 4 turns is better, but the efficiency is still not so great. It is better to make a second link and put it around the smaller coil for use on the higher bands.

[KA8WTK]

Thanks Patrick,
  I had found the part where you were test mounting the unit, but missed the part about the mod.

Bill