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CTC-16, an early command control system based on the commercial Digitrack 1600 system.


A 16 channel system, superseded by the Railcommand system. Appeared in 1979. Model Railroader magazine published it as a do-it-yourself project. Based on the Digitrack 1600, with simpler construction using newer integrated circuits available at the time. For example, GE's ASTRAC had a total of two semiconductor devices on the receiver. The CTC-16 used more than 10,300 transistors. (January 1984 Model Railroader)

CVP Products was one of the suppliers of CTC-16 systems. Mann-Made Products sold a version called Digipac 316, originally a 16 channel system that was later upgraded to 32 channels.

History of the CTC-16 Project

The CTC-16 was built by following a series of articles published in Model Railroader beginning in December 1979. The reader could construct the system himself following the instructions from parts that were easy to obtain.

Digitrack 1600

The CTC-16 is the second generation of the Digitrack 1600.

The Digtrack 1600 was a command control system offered by Electro-Plex. The system was designed by company founders, Charles Balmer and Richard Robbins. They began selling the Digitrack 1600 in 1972, which featured solid state electronics and digital command signals superimposed on a constant DC voltage. It was a step in the right direction, but it was costly. The system did not sell well, leading to Electro-Plex discontinuing production and sales of the Digitrack 1600 in 1976.

Model Railroader Magazine's Involvement

Shortly after Electro-Plex ceased production of their Digitrack system, Model Railroader purchased the publication rights for the system. Russ Larson, editor of MR at the time, thought that this would be an excellent do it yourself project for the magazine. They prepared a set of instructions, and as time went on, Larson began to realize the project would require a lot of resources from the magazine, be complicated, and have limited appeal.

The material was turned over to Keith Guttierrez during the summer of 1978, who reviewed the project and reported back to Larson. Guttierrez, an electronics engineer working for a large semiconductor company, felt the project was too complex, and would be costly, if not difficult, to build as presented. He also expressed the opinion that it may even harm the evolving concept of command control.

He did offer Larson something else: He would update the design of the Digitrack system, using newer components and technology that had advanced since 1972, plus create a set of instructions which could be turned into a series of construction articles for the magazine. Russ Larson thought that was a great idea, and the project began.

CTC-16 Design and Construction Phase

Guttierrez began working on the project, knowing that the advances in integrated circuits (chips) would mean that he could do more with fewer chips. He felt he could create a new, compatible version of the Digitrack 1600, with the same functions, but with a large reduction in the parts count, while reducing the cost. By December 1978 he had finalized a design that was no more complicated to construct than a transistor throttle. Preparation of the instructions began, then the assessment of the instructions, prototyping and the final product tests were underway.

Once that phase was completed and the identified problems corrected, the magazine articles were prepared and later published as a do it yourself series of articles in Model Railroader.

Publication of the CTC-16 Series

The first article of the series was published in the December 1979 issue of Model Railroader, introducing the CTC-16 system, while stating you could build this four channel analog command control system yourself for less than $200. The system was fully expandable to 16 channels, at additional cost.

Kits of parts with a PCB were made available, as well as a bare PCB you could populate with parts sourced yourself.

The $200 cost estimated in 1979 would be equivalent to about $650 today. It may actually cost less to build a CTC-16 today with equivalent parts.


The CTC-16 was compatible with the time domain multiplexing used by the Digitrack 1600. Sixteen channels were available, and 16 pulses were superimposed on the DC track voltages. The throttles were polled 125 times a second, and their settings were transmitted to the track.

As there were no standards for command control in 1978, CTC-16 was only compatible with itself and the Digitrack 1600. Other systems were not compatible with the CTC-16 nor each other.

Sound systems which sent signals over the rails were also incompatible with the CTC-16.

Track Detection

The CTC-16 was compatible with the Twin-T and other detectors commonly used, but not with any type that used a transformer which could distort the signal and cause erratic operations.


The CTC-16 could be built easily using readily available parts, and low cost parts could be substituted without many problems. It didn't require any special tools either. Anyone who had some experience building electronic kits would have few problems following the instructions.

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Commercial versions of the CTC-16 also appeared, such as the DIGIPAC 316 in 1984.

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