Correction to what was stated a few posts above about compound steam locomotives staying in synch necessarly  T'aint necessarily so.  Both types of locomotives, simple and compound, get out of synch.   There are many videos on youtube of the UP Challenger out of synch, but also Y6b Mallets on the Blue Ridge with their drivers clearly out of synch.

There are four chuffs per revolution of any of the driver axles on a steam locomotive because there are necessarily, by virtue of their mechanical valve events, four emissions of exhaust steam during each revolution of any one driver.  The valves slide back and forth in their races, whether slot or cylinder, atop their respective pistons which are doing the same thing.  Between them are two ports.  The valves slide over the ports and away from them, closing and opening them respecitvely, depending on where the linkages force the valves to be in their reciprocating travel.  They are always either a little behind the movement of the piston in relation to passage past the ports or timed to open as the piston reaches its extreme Nand stops.  Unlike an internal combustion engine where the spark happens very close to top dead center, but not before it or you get knocking, the steam locomotive's pistons must begin their return trip down the cylinder before the steam is admitted to accelerate them, but it is also cut off by the valve passing over the port and closing it again, prior to the piston reaching its furthest extent at the other end of its travel.  By letting the amount of steam admitted to expand and to do the work it can of forcing the piston forward ahead of it, there is more economy than there is by letting the port stay open and continuing to admit steam until the piston ceases its motion and begins its movement back the other way once more.   That is what is meant by the term 'cut-off', which is when the admission of steam is cut off and what has been admitted is allowed to expand and spend itself.  This happens mostly at greater speeds, but not at start-up when lifting a train from a dead stop.

So, if two cylinders each have two exhaust events, and the two cylinders are cycled 90 degrees apart in the 360 degree cycle, there must be four separate exhaust chuffs that the ear can detect, which is always the case.

First, about brake fluid:  beware that some varieties are hygroscopic.  They absorb water, including from the air around them.

Secondly, in the six years I ran my layout, it sat...a LOT!  I never had to clean it.  Ever.  Forced air furnace, carpets, pet, laundry in the same room with shaken towels and sheets, etc.  Ever.  I did have some touchy contacts at points, but a gentle wipe with 600 grit paper always seemed to clear the problem.  I have a Bright Boy, but why would I use it in view of my claims just now?

I was about the decommission my layout, so last fall I placed a few drops of Castrol Dextron III Mercon ATF here and there.  I actually was pretty liberal with the stuff, making sure there was enough for the train to distribute.   Result?  Didn't hurt.  Didn't seem to improve anything because............everything was doing fine anyway.

I think running metal wheels, cleanish ones, is about the best thing you can do for your track.  I dunno why I think that because.............I never had problems in the first place.  Rails sat for weeks at a time.  With laundry nearby.

Thank-you, gentlemen.  I figure I can get a decent sized speaker in there, but I may have to mount it at an angle and craft a custom-fit enclosure for it.  The Lionel HO Challenger tender from a few years back has such an arrangement.

I appreciate your quick responses, and acknowledge the effort of Jerry's HO in providing links with more information. 

Please tell me what size of a speaker would fit in this tender?  Is its interior molded/machined to take a speaker already?

Thanks in advance for your help.