A collection of old HO scale model railroad items came my way recently -- some track, locomotives and cars, and three power supplies all with the name 'hobby transformer' on them. 'Hobby transformer' seems a curious term to me, but that's what they're called. In this post, I'll look into the three hobby transformer units, and maybe learn a little about HO scale model railroading.
Bachmann Model No. 6604
Here's a view of the top of the first hobby transformer.
The "MADE IN CANADA" part suggests that the unit is decades old.
The cover is fastened by two folded-over tabs underneath; the manufacturer evidently meant to deter user access. The tabs can be straightened out, though, and the cover removed.
The wire-wound rheostat can be seen in its off position.
Underneath the rheostat is a very odd-looking rectifier assembly.
That's a rectifier construction that I've never seen before.
I've reverse-engineered the whole thing. Here's the schematic.
It's a centre-tapped, full-wave rectifier, basically. Note that the 'AC ACC' (AC ACCESSORIES) output is obtained from only one half of the transformer's secondary. That strikes me as poor utilization of the secondary, but it evidently works.
Anyway, I gave the slide switch a shot of WD-40, and reinstalled the cover along with some pieces of stiff insulating paper that I didn't show in the above photos. Reassembly was a chore. The unit is not pleasant to work with; the construction of it is cheap and sleazy so as to keep the cost down. It's a design that's meant to be durable from the factory so long as it's never monkeyed with. The unit works fine with the locomotives that I have. And so, it's on to a Tyco hobby transformer that's flat-out dead.
Tyco Model No. 899V
This one's cover is really fastened securely -- two folded-over tabs underneath and four 1/8" hollow rivets. I drilled off the rivet heads and got the casing opened up.
Unfortunately, the transformer's primary winding is open. That's too bad because this is a nicer device than the Bachmann unit that's still working. The construction is crisper, without the ambiguous fits of the Bachmann. Anyway, here's the schematic.
A very neat and tidy design with a full-wave bridge rectifier. The part number on the bridge rectifier looks like "WL 0058". That part number doesn't show up at all on a Google search. The bridge rectifier appears to be ok; it's only the transformer that's at fault. Oh well, on to the third power supply.
TRAINPACK MODEL 100 by MODEL RECTIFIER CORPORATION
This one looks very nice, with a large speed control handle. It's line cord plug had been cut off for some reason or other. I replaced the plug and the unit works.
The cover is held on by four Tri-Groove headed screws. It seems that the makers of hobby transformers really don't want users to have access to the things' innards. Tri-Groove screwdrivers are not easy to come by; I don't have any in my tool collection. The only way I'll be able to open up this unit will be to cut slots in the screw heads with a Dremel cut-off wheel. Here's a view of a Tri-Groove screw head.
And here's the screw head slotted.
And here's a screw removed.
It's a No. 6 x 1/2" threading screw. I have some No. 6 x 3/8" hex washerhead threading screws on hand that will do fine as replacements. So, it's on with slotting the remaining three Tri-Groove screws and getting the power supply opened up, whether the manufacturer would like me to or not.
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And here we have a view of the unit's innards.
There's what looks to me like a selenium rectifier, which would date this thing back to the 1950s. The glass tube component might be a self-resetting circuit breaker. Here's the best I could do for a schematic.
Like the Bachmann device, it's a centre-tapped, full-wave rectifier.
So there we are -- three ancient HO scale model railroad hobby transformers. Aside from the one with the transformer failure, they're certainly durable items.
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Update: A New Transformer For The Tyco Model No. 899V -- FRIDAY, MARCH 8, 2019
I went for a rummage through my stash of AC adaptors, and came up with this item.
Its AC output is about what's needed to replace the bad transformer in the Tyco 899V. Now if the transformer inside that casing is the right physical size, I'll have the makings of a very neat repair job.
I sawed open the AC adaptor's casing for a look-see.
And no such luck. The transformer is considerably larger than the one inside the Tyco unit. That's not game over for this project, though. It just means that I'll have to fit out the Tyco unit with a coaxial power receptacle to mate with the AC adaptor's output plug. Then the Tyco unit can be made operable again.
Here's the receptacle I'll be using.
That just needs to have a 5/16" diameter hole drilled in the Tyco's chassis to accept it.
And here we are with the line cord and the dead transformer removed, and the receptacle installed and wired up.
A rear view.
And a front view.
I plugged the hole left by the absent line cord with a 1/2" rubber grommet-style hole plug.
The unit now works perfectly -- as if that AC adaptor I found had been designed for it.
Now I just have to glue and seal the AC adaptor's casing back together, and this 'hobby transformer' will be good to go.
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