Hi
The Lionel electric trains from the fifties and before, had a transformer to control the speed, AC. What was doing the variable voltage ? A simple series rheostat ? Thyristors did not exist then... Never opened mine then; at that age would had not understood its bowels either.

 

Likely it uses a transformer with the secondary winding having a bare side with a sliding contact like an variable autotransformer (variac).
That would be both efficient and relatively simple.

3 cheers for the deciBel!!!

 

A similar thing I had as a lad used a series rheostat.

 

Something like the Scalectrix, at least in the beginning?

 

Likely it uses a transformer with the secondary winding having a bare side with a sliding contact like an variable autotransformer (variac).
That would be both efficient and relatively simple.

3 cheers for the deciBel!!!

I used one as a source for low voltage AC at a few amps of current. At one point I was using it to power a stereo where the power supply transformer had blown its primary winding. I back fed it using one of the secondary windings.

 

I used mine (well, one for an HO-scale train set, don't recall the brand) to drive a water electrolysis cell. I didn't care that it was AC because I was collecting both gases together to make loud noises.

 

Likely it uses a transformer with the secondary winding having a bare side with a sliding contact like an variable autotransformer (variac).
That would be both efficient and relatively simple.

3 cheers for the deciBel!!!

I did take mine apart. That is exactly what I found.

 

In the mid-60s, I had an HO scale race car set. I opened a speed control gun and found a bare wire wrapped around a Mica slide. Squeezing the trigger slid a metal bar across the coil, making the car go faster or slower. My HO scale electric train set had a more refined rheostat with four points of contact: a center contact connected to the center tap of a “Probably” 12-0-12 transformer. Diodes connected on either end controlled the direction of DC flow. By swinging the lever one way the train moved in one direction. When swung the other way it would reverse direction.

 

I did take mine apart. That is exactly what I found.

I'm pretty sure the transformer for my old Marx train was also built that way.
Below is basically how it looked, except mine had an extra set of terminals with steady 13Vac out for accessories like lights or switches:

 

Note that these Lionel transformers, some are very old.
They have no primary fuse, and only later years had a circuit-breaker for the track output.

I remember getting short-circuits on the track and things smoking and glowing. They put out many amps. Just running a locomotive the sparks off the wheels was impressive.
The short-circuit was in #020 90 degree crossing.

 

I'm pretty sure the transformer for my old Marx train was also built that way.
Below is basically how it looked, except mine had an extra set of terminals with steady 13Vac out for accessories like lights or switches:

View attachment 359855

Wow! Look at the odd plastic that that is made out of. Never seen anything like it.

 

The old LIONEL transformers certainly do have a transformer with a sliding tap on the secondary. AND they had no overload protection at all for many years. I disassembled a couple of the larger ones that were totally burned up inside. A circuit breaker or other overload protection would have been a vary big value-added feature that would have sold.
All of the "HO" trains at that time were DC powered. The Lionel system used a noisy drum-relay to revers the motor field so that the train could back up.

 

A circuit breaker or other overload protection would have been a vary big value-added feature that would have sold.

But then they wouldn't have "New Transformer" sales. Had they included a fuse then they could be user fixed. And no business wants anyone fixing their equipment. They'd rather sell new.

Mother-in-law's washing machine had a failed mode shift coil. An item that could have cost as much as $45 to replace. But they wouldn't sell just the coil, they wanted to sell us a whole new mechanical assembly at a cost of $135.00. Then there was either the time and energy trying to disassemble the old stuff and installing the new stuff. Of course you could have simply unbolted the coil and moved it over to replace the failed machine.

Not me! I disassembled the coil and found a blown Fusible Link. It was rated for 102% of the anticipated normal use. In other words it was going to fail soon no matter what. But I went to RadioShack and bought a Fusible Link for $1.98 plus tax. removed the old link and installed a new link, one that was rated for 145% normal operation. It still provided adequate protection and didn't cost $45 or $135. For little more than $2.00 it was fixed. Last time I saw that machine it was still running. Mom's been gone 3 years now, but the machine is in the hands of her son. Far as I know - it's still working.

As for the transformer, poor engineering dictated that some kid was going to drop a penny on the track just to see what it would do. To their chagrin they found out what happens when you dead short a transformer secondary. Quite possibly a few burned fingers too from picking up a hot penny.

 

One unprotected transformer burning up under a tree and starting a fire would probably have generated enough bad press to cancel all of the profit from selling replacement transformers.
At this point I regret not creating an external fuse or circuit breaker package to protect from transformer overload damage. I could have been a wealthy 12 year old if I had done that and had any kind of decent marketing operation.