Dynamotor replacement plate, bottom view
I have never been fond of replacing the dynamotor in BC-224 and BC-348 receivers with 115vac supplies mounted on the old dynamotor bases, but I can understand why it was the thing to do back in the day. I still lean more toward building an external supply if one wants to keep the internals of the receiver unmodified, because it is easier to work on RF interference issues and it eliminates another source of heat within the receiver cabinet. On the other hand, the relatively recent availability of inexpensive 12-24vdc switching supplies has made it more attractive to mount one internally if you have the patience to shield and bypass it in an adequate manner. For those who consider doing that and can't find a old modified dynamotor base to support the whole shebang, below is a fabrication sketch of a simple 1/16" thick aluminum plate that will drop in the same space. At least it forms a starting point.
This particular plate was made for a friend who wanted to try one of the ebay supplies without changing anything inside his receiver. I had a Cinch-Jones five terminal strip handy, so I mounted it underneath the plate with a setback of .688" from the end of the plate to match the setback in the original dynamotor bases.
Layout of this plate starts simply with cutting out the basic rectangle, 6.312" x 3.675". Using the top right corner as the reference point, you can scribe all the feature dimensions on the plate and cut them out appropriately, using the top and right side as references.
A dowel post was added to BC-348 receivers to prevent accidental use of the 14 volt BC-224 dynamotors on the 28 volt BC-348 - a good example of GI-proofing, since making a mistake the other way around doesn't hurt the dynamotor for short periods and a tech could find the problem pretty quickly with less than half B+ on the high voltage buss.
