TRANSMITTER No. 23

P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
TELEPHONES
GENERAL
Z 3014
Issue 7, 18.4.52

TRANSMITTERS NOS. 23 AND 23A

1. General
"Transmitters Nos. 23 and 23A" are breastplate-type instruments for use on C.B. and L.B. systems.

"Transmitter No. 23" is provided with a switch facility and supersedes "Transmitters Nos. 4 and 5". It is for use by operators at phonogram rooms, and by supervisors. "Transmitter No. 29A" (without switch facility) supersedes "Transmitter No.5A" and is for general use by operators. Both transmitters are now being issued in Mark 1, Mark 1A and Mark 2 types.

2. Description
Mark 1  "Transmitters No's. 23 and 23A" include "Mouthpiece No. 17" and have a fixed contact for the back electrode of the transmitter-inset.

Mark 1A transmitters are similar to Mark 1, except that they have a "Mouthpiece No. 19" and "Transmitter No. 23, Part 9/62256" (cover for a Mark 2 transmitter).

Mark 2 transmitters are similar to Mark 1A, but have a floating contact for the back electrode of the transmitter-inset.

Apart from the switch facility (see par. 1) and the type of transmitter-inset, the parts of "Transmitters Nos. 23 and 23A" of the same Mark No. are identical, and are as follows:-

1. Moulded breastplate, to which is attached the main moulding and the usual webbing_.

2. The terminal-plate cover, which is fixed by the right-hand large screw at the back of the breastplate

3. Moulded packing-ring, covering the inset and fitted with the plain surface outside

4. Transmitter cover, carrying the acoustic filter and the mouthpiece

5. Mouthpiece No. 17 or No. 19 [see par. 3(a)]

6. "Transmitter-insets Nos. 134 and 134A" for "Transmitters Nos. 23 and 23A", respectively. [NOTE:- Items (b) to (f) may be requisitioned separately]

3. Replacement of parts

(a) "Mouthpieces Nos. 17 and 19"
Due to a difference of thread, these items are not inter-changeable. When a "Mouthpiece No. 17" is broken, a "Mouthpiece No. 19" should be fitted. To do this it will be necessary to replace the existing transmitter cover by a "Transmitter No. 23, Part 9/62256". The replaced cover should be scrapped, unless it can be used-up locally. "Mouthpiece No. 17" has a short rectangular thread, with sharp•corners formed in the material of the boss, and a white spot 1/16in. diameter marked on the outside of the boss. To remove the mouthpiece, move the nickel-plated catch at the side as far as possible towards the breastplate and unscrew the mouthpiece. To reassemble, slip the mouthpiece into position, with the white spot adjacent to the catch, screw up, and lock the catch. "Mouthpiece No. 19" has a long rounded thread, and no white spot. To remove and reassemble the mouthpiece, the same precautions apply generally as for the "Mouthpiece No. 17".

[NOTE:— The mouthpiece number is marked on the side of the boss, but some "Mouthpieces No.19" have been wrongly marked "No. 17": they can be recognized by the type of thread].

(b) Acoustic filter
When the mouthpiece is removed, the acoustic filter is exposed. This is a tubular fitting with a knurled collar, which fits in the opening in the transmitter cover.  Investigation has shown that this filter is of little value and, if damaged, it should be scrapped. This filter will only be found on earlier types of "Transmitters Nos. 23 and 23A".

(c) Transmitter-inset
Loosening of the right-hand large screw at the back of the breastplate permits the removal of the terminal-plate cover. The transmitter cover is then removed by loosening the left-hand screw at the back of the breastplate by three or four turns, and then rotating the mouthpiece until it is parallel with the breastplate, at the same time lifting the cover away from the main moulding. The moulded packing-ring and the transmitter-inset can then be lifted out. The following points relating to both types of transmitter-inset should be noted:-

1. 'Transmitter-inset No. 13A" is provided with an insulating ring in the spring-retaining disk. The function of this ring is to provide a switching device, and care should be taken when replacing the inset to ensure that the spring projections on the disk register correctly with the slots in the transmitter cover.

2. "Transmitter-inset No. 13AA" is similar to "Transmitter-inset No. 13A", but the insulating ring is not provided in the spring-retaining disk as the switching facility is not required (see par. 1),

["Transmitters No. 23A" were previously fitted with "Transmitter-inset No, 13" (minus guard),  In future faulty "Transmitter-insets No. 13" should be replaced by "Transmitter-insets No. 13AA"].  "Transmitter-insets No. 13AA" should also be fitted on "Transmitters No. 23A Mark 2" when, due to the fortuitous rotation of the "Transmitter-inset No. 13", trouble is experienced with the flexible lead winding round the transmitter plug and subsequently breaking.

"Transmitter-insets No. 13AA" can be obtained on M.E. requisitions, which should be endorsed "For use in "Transmitter No. 23A"; "Transmitter-inset No. 13" (minus guard) will be returned when this is the case.

(d) Broken lead
Broken flexible lead to back electrode of the transmitter-inset in Mark 2 transmitters. To replace a broken flexible-lead to the plug in the Mark 2 transmitter:-

1. Remove the main moulding from the breastplate, by removing the two small countersunk screws in the back of the breastplate.

2. Remove the broken portions of the lead from the plug and connexion tag, and replace with in. of "Cordage, Instrument, No.1/E, Black", threading the cordage through the hole drilled in the moulding.

3. In the earlier issues of transmitters, the flexible lead enters the transmitter case via a slot in the moulding and for this design it is necessary to press the cord into the bottom of the slot in the transmitter case, and fill the slot with "Compound No. 2", by working with a warm iron. Take care that the compound is pressed tightly on to the cord, and also that it does not project above the slot, as it would then interfere with the rotation of the transmitter-inset.

Note:- Where a local stock of "Compound No.2" is not held, it should be requisitioned specially only if large quantities will be used. The black insulating compound used to seal the tops of dry batteries, e.g. "Battery, Dry, No. 8", is a suitable substitute and should be obtained from scrap batteries. Alternatively, a small supply of pitch may be obtained locally.

Last revised: December 11, 2023