TCS Transmitter

I am currently trying to bring to life a highly modified Collins TCS transmitter. It's previous owner a W9 has had several modifications done to it. Currently this is what I found.

Front panel and case replace by a homebrew ( nice job). It can now go in a rack.

All of the relay keying has been removed, as well as the tr switch.

The series parallel tank circuit has been modified to a combo pi net.

It has a speech amp added to drive the 1625's in class B zero bias

The roller inductor used to match random wires in the original, has been removed

A bias voltage was added to the 1625 finals

The mechanics of the mods were very well done. I figured to build a supply ,add the tubes and fix a few small items and be on the air. Well , it didn't quite turn out that way. I built up a supply and got it on the air easy enough on cw, but the finals were very hard to tune. The modulator speech amp that was added in place of the original crystal deck, did not work. It probably never worked, I found several wiring problems. After playing with several solid state designs for a quick speech amp I decided to gut the old tube amp build my own. It consists of a 12ax7 and a 12au7. It worked ok , but didn't have enough to drive the 1625's wired in class B. It would drive it well with about -18 volts on the grids on the mod tubes. After consulting with Andy WA4KCY on the class b stuff, I decided just to leave the bias in and go. I got good audio reports from Sam KF4TXQ on 3885 khz, so I feel pretty good about the modulator. The other items I added were a PTT and a spot switch, as for the RF quirks in the tank circuit, I am still working on it. More info as progress is made.

This is a picture of what the TCS looks like unmodified. This is my original transmitter and receiver.