D.C. Power supply

Here are some...

https://www.ebay.com/sch/i.htm...leDesc=0&_sop=15

trainman129 posted:

 

Seems to have been back about the mid sixtys. The transistor was mounted on a heat sink for cooling. 

Is that a typo?  By mid sixtys you mean 1960's? 

Search eBay for "pwm motor controller" and you'll get thousands of listings suitable for a DC-motor trolley (i.e., just a few Amps of current required) starting at less than $2 (free shipping from Asia).

No direct links to eBay allowed on OGR but here's an image of one that even has a reversing switch.

You need a source of DC voltage.  But you can get a wall-wart with, say, 12V DC output capable of several Amps for less than $5 (free shipping).

I already have a DC power supply. All I need is the simple transistor circuit for control. I know I saw one published years ago but have no memory of where.

There are no direct links to your own auctions on the forum but we reference eBay all the time for stuff. 

Why don’t you just use a dc transformer/power pack from a train set? They can be had quite cheap

You'll need a bigger Q2 than a 3904, depending on the current you are controlling. Probably a 2N3055 and a quite big heat sink.

I think you sounded a bit unfamiliar with how to design a transistorized adjustable dc voltage regulator. No mention of parameters, etc. So most of the reply posts would naturally steer you to some finished products that most of us who might have designed lots of regulators in the past have gravitated to out of sheer laziness and cost considerations. Much of what you can find on ebay is cheaper than constructing it your self and quite suitable.

If you want to design your own, Google "transistorized adjustable dc voltage regulator" and you will come up with thousands of examples just as I did in the last post.

For an even heavier duty adjustable regulator that's simple to build, consider the LM338, it's a 5V adjustable regulator similar to the LM317.  Same circuit, just add the bridge rectifier and a nice healthy filter capacitor, probably around 4,700uf to start.

As Chuck stated, it's probably easier to just buy the module on eBay, tons of options.

I just picked up one to control the speed of my turntable motor.  Works well, and was under $10.  May be the one Stan showed above.  But I did get it from a US source and it came in a few days.  If you want it, I can dig out the info.  (May have been on Amazon.)

trainman129 posted:

...made up of a power transistor and a control pot. Seems to have been back about the mid sixtys...

I built a couple of these in the 70's for a friend on his HO layout, the circuit was in MR or RMC, the parts were available at Radio Shack, I do remember the transistor was in a TO-3 case.  I still have the original magazine, but it is buried around here somewhere.

HERE is a very close circuit to what we were using.

As pointed out previously by GRJ, those adjustable voltage regulator chips (LM317) are pretty versatile. I used one as the centerpiece of a loco RC system I designed in 2011. Circuit diagram attached.