Replacing the disk rectifier on a Lionel 167C whistle/direction controller

[T Norm]

Hello: I am new to this forum but I have used this site to help me a lot on my O guage railroad hobby. I have a 4 by 26 foot layout with a mainline and a double siding powered by a Lionel Z transformer. I use the D post for my main line with 4 lock-on in parallel and the C post for my sidings with one lock-on. I have used and used up two 167 whistle controllers ( the first one that melted did not a the circuit breaker-smelly ). I was thinking that replacing the disk rectifier with a diode, (5 amp 1000 volt fast recovery) in my current 167 C (with the circuit breaker), will help it run cooler as it currently get warm to the touch when I run my whistle tender. I removed the disk rectifier, and refering to the service manual for the 167C  I soldered the cathod end of the diode to Contact C on the whistle side and the anode end to the wire that goes to the Choke Coil. Then I wired in the 167 and nothing. The resistor that was in parallel with the now removed rectifier was soldered to Contact D. Should I have soldered the diode to that contact? Any help would be appreciated. 

[wrmcclellan]

Hi Norm,

We'll need input from Lionelsoni (Bob) regarding the orientation of the diode.

The old disk rectifiers and the resistor dropped about 4-5 volts and the newer diode you have only drops about 1 volt. Not sure if the difference in voltage drop has an affect, but the newer Lionel controllers have 4-5 diodes in series to get the voltage drop to activate the whistles/bells.

[wrmcclellan]

Here is an interesting thread about the Lionel 167 and modern era 6-5906.

https://ogrforum.ogaugerr.com/topic/lionel-6-5906-sound-activation-button#2415514336840886

 

[lionelsoni]

The diode is shown backwards on Lionel's 167C schematic diagram, as it is on all the older transformer diagrams.  However, that matters only if you are running a modern locomotive that distinguishes between bell and whistle, in which case the whistle button should make the center rail positive.  In any case, you can simply interchange the controller terminals to get the same effect as reversing the diode if you need to.

The copper-oxide rectifier does have a smaller forward voltage drop than a modern silicon diode, but substituting silicon for copper oxide is not enough to significantly degrade the 167C's performance.  The copper-oxide circuits used in the 167C and in the transformers do not exploit that forward drop in the way that later whistle controllers with stacks of diodes do.

A 1000-volt reverse-voltage specification is a bit of an overkill, but harmless--50 volts would be adequate.  I would have gone for a higher current rating, since 5 amperes is right on the edge.  I don't see any advantage to a fast-recovery diode in a 60-hertz device like this.