A number of stations have been able to obtain some of the model 28 Reperforator-Transmitter (RT) sets at 100WPM that Navy MARS received from the State Dept. This month we will cover that unit and in particular the TD unit that seems to be giving everyone a hard time. The TD is called the LAXD. The LAXD is a climbing or pivoted head TD and is usually used together with a typing or non-typing reperforator. It is able to sense or read the last character that the reperforator has punched.
There are two clutch magnets (see diagram) in the LAXD TD. One is called the reader and the other the distributor. They are both 200 ohms and need 160 MA to close them. Teletype Corp. says 48V direct current is required for each one. Now before you go run and connect them in series, read on.
The thing that confused most, including myself, is that the clutch magnets can not just be connected together. (for example, in series) The important fact that was discovered before I had any diagrams is that: the reader clutch magnet and the reader cam shaft together with the distributor clutch contacts control the distributor clutch magnet. This means that BC15 and BC22 (see diagram) must be connected in series with the distributor clutch magnet circuit. This is very important, otherwise the unit will not function properly. As you can see 1000 ohm 5 watt resistors were added to each circuit (see figure 2) to in able the circuit to work on 115 VDC. If you have 48 VDC, the resistors can be removed. I have not tried the unit with AC. If anyone does and it does work let me know. The transmitter stop contact (BC25 and BC26) it the control which stops the pivot head when it hits the reperforator punch block. The trans aux. (BC13 and BC24) and dist. aux. (BC 9 and BC8) are not used. They are intended for two cycle operation. Can't think of another use for them. If anyone finds a use for them let me know. I think figure 2 should pretty well cover the TD control circuits.
The only other circuit is the signal line. The code reading contacts must be connected in series with the distributor contacts as shown in figure 3. All of the connections for the TD are brought to a 32 pin connector (female) on the back of the base of the RT 28 unit.
The reperforator LPR is also terminates in a 32 pin female connector on the back of the RT 28 unit. The only connection that is necessary is the sig-nal line to pins 14 and 15. The selector magnets can be connected in series or parallel depending on which you use. (60 or 30 MA) 60 mils is common so you will probably want them in series.
[ed. note - parallel?]
I suggest that a power supply giving 115 VDC at 300 MA be constructed and all of the connections for the unit be made in the power supply. A male plug can plug into the unit and the other bought to the power supply and terminal strip. The signal line might be brought to a female phone jack for patching into the other TTY circuits in the shack.
We are using two of these RT 28 units here at NAV-2 with very good results. The storage bin is great for storing up to thirty messages of average length for later transmission. We do not use the tape winder because it curls the tape and makes it very hard to retransmit. We let it fall into a plastic waste basket. We were lucky to obtain a cabinet that houses two of the units with power supplies. A great deal of modification was necessary to the cabinet. I am going to make this info available to N0RTP/W4PFC as soon as I get them into a finished form. They are the only other ones I know of that have a cabinet.
