[GreenKeys] Model 28 TD - use of dual shaft (LBXD) vs single shaft (LXD)

[John, W9DDD]

I've seen references to business machine (IBM?) useage.  The FAA liked 
them.  They previously used a version of the 14 TD that had a 32 (24?) 
pin slip connector instead the standard 9? pin connector.  You could 
read the tape or you could send 5 bit by the means of external logic.  
Only one at a time. The two shaft LBXD could do both at the same time.  
I suspect th FAA was the original reason for the LBXD.

Did ya mean LX for the 5 wire output?  Or an LXD with the modification 
kit to add contacts to the reader pins or LD for 5 wire input

Weren't were looking for some FAA WDs related to the FAA use of same? A 
WD package for ADIS perhaps labeled as a specification?

On 7/23/2026 10:38 AM, Nick England via GreenKeys wrote:
> I got to wondering about where the dual-shaft TD was used.
>
> BACKGROUND FYI -
> The single-shaft LXD has a single clutch magnet and operates with
> direct action from "read the holes" to "key the loop" on every cycle.
> The dual shaft LBXD has two clutch magnets with a transmitter shaft
> (read the holes) and a distributor shaft (key the loop). They can
> operate together (via a contact on the transmitter camshaft triggering
> the distributor magnet) or separately - the 5 lines from the
> transmitter and 5 lines to the distributor are brought outside so
> "multi-wire" data can be read and/or inserted into the serial loop.
>
> QUESTION
> SO, I know the dual shaft versions are used in torn-tape transmitting
> equipment where message header characters are inserted between TD
> transmitter and distributor. And anywhere else that would be useful.
> I'm not clear about where else they would be used.
> Al K8WXQ has a 28ASR with LBXD but the 5 lines are just wired straight
> from transmitter to distributor (This is its original configuration).
> - so why is the LBXD used in that ASR instead of an LXD?
>
>
> Note - there was also a single-shaft LXD with 5-wire output so you
> could use that to drive something - I have a piece of torn-tape gear
> that recognizes ZCZC, FM, TO, BT, etc, that way.
>
> So MANY Teletype variants!!!
>
> Cheers,
> Nick England K4NYW
> Chapel Hill NC
> www.navy-radio.com
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The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD