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

[Nick England]

Thanks John.
1) Yes I have a table-type dual TD with two LBXD. We swapped email and
suspected it was FAA although it came from an SK who worked for Norfolk &
Western Railway.

2) I have an AN/UGC-71 multiple address message processor that has an LXD
TD with 5-wire output.
https://youtu.be/WXWpx36RF04

Nick England K4NYW
Chapel Hill NC
www.navy-radio.com

On Thu, Jul 23, 2026 at 2:49 PM John, W9DDD via GreenKeys <
greenkeys at mailman.qth.net> wrote:

> 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
> > ______________________________________________________________
> >
> --
> ---
> ----
> The above comments or recommendations are SWAG. Use at your own risk.
>
> John, W9DDD
>
> _____________________________________________________________
>
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