Postwar ZW Voltage Drop When Using Whistle

When the whistle control is not being used, the roller arm, which is tapping the transformer coil that provides the variable voltage, is connected to the "A" binding post.  When the whistle lever is moved to the whistle position, the roller arm is disconnected from the "A" binding post and is reconnected to the five volt compensating winding, then the rectifier, then to the "A" post.   In the circuit connected when the whistle lever is operated, the compensating winding is unlikely to be the problem. Look at the rectifier and the whistle switch contacts.  Those are probably the devices most likely to cause a loss of voltage when the whistle lever is operated.  

Since the whistle blows, the rectifier and resistor must be OK. I suspect dirty switch contacts.

Unplug your transformer.
Remove cover
Vacuum out any loose dirt from the switch.
Cut strips of index or business cards to fit into the opening between the plastic switch piece and the fiberboard plate. (try to keep it wide).
Work the strip down, getting it between the spring contacts on the plastic parts, and the button contacts on the fiberboard. You probably will need to move the switch back and forth a bit. Once the strip is all the way in, work the switch a few times.
Carefully remove the strip. It will probably have streaks of black

When I do this, I also use a strip moistened with 100% pure mineral spirits (some has water added)., followed by another clean, dry strip.

You have to be patient and careful. Don't want to damage the contacts, or leave pieces of index card behind.

C W Burfle posted:

Since the whistle blows, the rectifier and resistor must be OK. I suspect dirty switch contacts.

Unplug your transformer.
Remove cover
Vacuum out any loose dirt from the switch.
Cut strips of index or business cards to fit into the opening between the plastic switch piece and the fiberboard plate. (try to keep it wide).
Work the strip down, getting it between the spring contacts on the plastic parts, and the button contacts on the fiberboard. You probably will need to move the switch back and forth a bit. Once the strip is all the way in, work the switch a few times.
Carefully remove the strip. It will probably have streaks of black

When I do this, I also use a strip moistened with 100% pure mineral spirits (some has water added)., followed by another clean, dry strip.

You have to be patient and careful. Don't want to damage the contacts, or leave pieces of index card behind.

Thanks for the instructions C.W., I'll see if I can get this done tonight. I'm heading out of town tomorrow so if it's not done by then it'll be another 10 days until I get around to it.