Introduced in 1932 this was a receiving valve amplifier for use on customers premises to assist persons who were hard of hearing.  Customers had complained about the Repeater, Telephonic No. 9 and the GPO Research Department redesigned the No. 9 with updated hardware and fitted the rheostat volume control inside a candlestick telephone.

The changes made cut production costs and thus cheapened the additional rental.  The resultant amplifier had an increase in volume and the volume control relocated, to the rear of the handset, on a newly introduced Bakelite telephone.  This meant that the volume control was easy to access and the amplifier could be located out of sight.

It used a Telephone No. 1/226 and Bellset No. 26.

This apparatus was produced in three variants, the No. 17A, 17B and 17C.

The No. 17B was introduced 1937 and was based on a design from a member of the public who had impaired hearing and had found the No. 17A not fit for purpose.  The member of the public was also involved in testing of the No. 17B.

The No. 17C was introduced around 1949 for use with Telephone, Intercom Nos. 1/1B and 1/2B and had a Relay No. 503D fitted.  The relay was used to switch the power on and off to the amplifier.

Repeater, Telephonic No.17A and No. 17C are single-stage triode valve amplifiers (Valve, Thermionic No.74 or Valve, Electronic CV 1673) in a wooden box which is designed to also contain dry batteries for the H.T. and L.T. supplies.  The amplifier box is suitable for wall or desk mounting.

Repeater, Telephonic No.17B is a single-stage pentode valve amplifier (Valve CV 1118) with tone control (located on the casing).  It is housed in a wooden box together with the dry batteries for the H.T. supply.  The box is suitable for wall or desk mounting.  The L.T. supply is obtained from dry batteries housed in a separate box, called Boxes, Battery for 3 Dry Cells.  This was 13.5db louder than the No. 17A.

Batteries used were two Cells, Leclanché DR2 for all variants with one Battery Dry No. 2 for Nos. 17A and 17C and two Battery Dry No. 2 for the No. 17B.

The case material was made from either Walnut or Mahogany.

The No. 17A superseded the Repeater, Telephonic No. 9A.
The Handset No. 4 superseded the Repeater, Telephonic No. 17A.

Specification D925 (17A).
Specification D1903 (17B).
Specification D1766 (17C).
s 9805 & 9005 (17A and 17C).
Diagram LD 37 (17A).
Diagram LD 127 (17C).
Diagram SA 4036 (17B).


Picture dated 1952
The amplifier is controlled by the three buttons on the telephone
and there is a volume control on the front of the case.
It is not known if this telephone was ever made available and it may have been a prototype.


Picture dated 1952


Picture dated 1959
This picture is to show the size difference between the Repeater Telephonic No. 17A
and the Handset No. 4, which was it's replacement


BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: May 19, 2021