PostWar whistle tender question/problem

[GPJ68]

I've got a couple 2466 and 6466 PostWar whistle tenders that I've been working on getting running smoothly. One of the 2466's has a slight but noticeable hum/vibration as the power in increased to get it to sound off, the others work fine. All three will sound the whistle ok, it's just this one that has a hum - not sure how else to describe it - sorta like the light hum of a transformer. Not an e-unit buzz, and not real loud, just a hum. It does it the entire time power is put to the track, not just when the whistle button is pushed (using a Z-4000), and increases as the power is increased.

It's not acting like a major short - no sparks, no tripping the breakers, no noticeable extra power drain compared to the other whistles. Just a hum, and I can feel a vibration that also increases when I put my fingers on the metal car chassis (with the plastic cover off) and run the power up. Engines will run fine while pulling the tender and operating the whistle. It's just this hum that's bugging me - don't want a minor problem to turn into a major one - if it's really a problem at all.

Any thoughts?

GPJ

[Roger Bielen]

I offer an outright guess, Could it be possible that since the tenders use a DC current that the transformer output with a "distorted" AC be making the hardware act like there is a slight DC current flow????

[lionelsoni]

Until you blow the whistle, the only thing that should be connected to the track voltage is the relay coil. This is a special "slugged" relay that is intended to respond to DC but ignore AC. (The copper slug at one end of the coil is what gives it this ability.) The relay is built to be as sensitive as possible, so that it will respond to the small DC voltage that the transformer adds to the normal AC track voltage. The slug doesn't prevent all AC flux from getting to the relay armature--it just reduces it a lot. It could be that the little AC flux that gets through is enough to make the rather loose armature buzz a little.

You could test this hypothesis by stuffing some paper or a toothpick under the armature, so that it can't move, let alone close to operate the whistle, and see whether the buzzing stops. If it is the relay, you could fiddle with it and try to make it look as much as possible like the non-buzzing ones you have. Failing that, you'll probably have to replace it.

[GPJ68]

Looks like I got it.

I took your your tip lionelsoni, and wedged a small wood pick between the amature plate and coil base and twisted lightly to lock the armature down - hum went away. Then I found that the hum would also disappear if I squeezed the relay frame slightly in towards the chamber housing. So I stuck a wide thin washer between the relay frame top and the mount bracket on the housing, tightened down on the screw, and voila - no more hum! At least not until I run the Z-4000 up to @ 21 volts, then there's the barest hint of a hum. The relay looked and felt like it was tight on the bracket, and the screw was tight, but apparently not quite tight enough. Maybe the threaded insert in the top of the relay bracket had a little slop, or was uneven and not making full contact with the mount even with the screw tight.

Now I can put the shells back on. So where'd those screws go.......

GPJ

[ben10ben]

Every relay that I have ever worked on had a thin lock washer on the mounting screw between the bracket and the top of the relay. I have seen these occasionally split in half and fall out from being tightened just a hair too tight or for no apparent reason. Could this be what happened to you?

[GPJ68]

Ben,

There is a lock washer between the screw head and the top of the mount bracket ( a star lockwasher, not a split ring one) . There was no washer between the mount and the relay top. The extra washer I used I put between the relay top and the mount - the washer is large enough inside to fit around the threaded insert in the top of the relay frame - it (the insert) doesn't sit flush with the relay frame top, but protrudes slightly (at least it does on the "problem" whistle). Before, only the insert's top surface would be pulled tight to the mount bracket when the screw was tightened. Now, when the screw is tightened, the entire bottom surface of the mount bracket contacts the larger washer surface, the other side of which is in contact with the entire top of the relay frame, not just the insert. More surface area sandwiched together. The protruding insert fits inside the washer.

Maybe another washer used to be there, but fell out at some point as you've seen.

GPJ