Postwar whistle activation question

[Anonymous]

I noticed that neither whistle controller in one of my ZWs produces enough holding voltage to keep the relay closed.  I am running a 675, and I tried four tenders with the same result.  I was thinking about connecting an extra wire from post A to one side of a button, then connecting one end of a diode to the other side and connecting the remaining end of the diode to the center rail.  Pressing the button should apply the DC  at the same voltage as the track voltage.  Will this do any damage to the relay?  Any info would be appreciated.

[lionelsoni]

If I understand what you propose, your entire added circuit will be short-circuited by the direct connection between terminal A and the center rail.

The Lionel circuit first connects a rectifier diode in series with the regular transformer winding and the 5-volt "compensating" winding, to operate the relay, then shunts the diode with a resistor to allow a stronger AC component through and reduce the DC component of the voltage.  It seems possible that the resistor value has decreased somehow.

The resistor, ZW-87 or ZW167, is just a piece of resistance wire.  Is it possible that someone shortened it to repair a broken wire?  Or that a loop of the wire has shorted together to reduce its effective length?  In any case, you may be able to get improvement be adding resistance to it.  Unfortunately, I don't know what the proper resistance should be.

[Anonymous]

Bob,

          Thanks for the info.  I don't think the resistors are damaged, because the whistle controllers used to work.  I noticed that their performance seemed to deteriorate with use.  I put new rollers in the ZW a couple of years ago, and the whistle controllers did work, but they were iffy at best.  Maybe it is time to replace the copper oxide rectifiers.  

[Anonymous]

The problem may not be with the transformer. Those old whistle relays had a habit of getting balky. You need to do some testing with another transformer if you can find one. In any case take the cover off the tender and watch the relay. does it realy drop out or the contacts just dirty. Try cleaning and lubricating the whistle motor. Sometimes if it is too gunked up with old grese it will run but the increase current will cause the relay to drop out. I do not think the problem is with the transformer as you report that you have the problem with both buttons. Everything but the transformer windings are seperate. Just in case there is a problem that can appear with any of the old whistle transformers that can cause this problem. The contacts on the whistle switch must keep the diode connected during the complete movement. Sometimes they get dirty and lose the diode connection momentairly allowing the relay to drop out.