In early 1932, the Marconi Osram Valve company introduced a receiving valve which was entirely new in design. Called the Catkin, it was in a sense the baby brother of the external anode CAT valve.

A disadvantage of holding the electrode structure of a valve within a glass envelope is that this makes it difficult to conduct heat away from the anode. A way round this is to make the anode itself form part of the envelope of the valve. For many years this was done for large transmitting valves (see CAT9) where the anodes were cooled by air or liquid.

Like the bigger brothers the catkin valve has an external anode with glass being used only as an insulator. The anode is designed to be air cooled. The anodes of these valves run at a relatively low temperature of between 60 and 150C, and due to the overall lower temperature of the other valve components they do not need to be heated to the usual high temperatures during the outgassing processes. For example the anode temperature of a MPT4K catkin was 145C compared with 420C for the glass enveloped MPT4. This lower temperature gave the catkin a very long life.

Another advantage of the catkin was that the internal elements were held accurately inside the anode with mica supports. Bear in mind that this was the period before the more modern miniature valves, thus it compares with the bulbs of the time where the elements were basically held only by the support rods and connections through the glass to the pins. The catkin was significantly smaller than its traditional glass counterpart. Of note the catkin range was interchangeable with standard types, for example the aforementioned MPT4K was the catkin version of the MPT4.

Catkins used a circular seal with the leads positioned around the circumference and the exhaust tube in the centre. Of course the anode connection was made to the anode itself rather than by a lead through the base.

Finally catkins were held into the metal base shell by rubber, which helped keep vibration from reaching the valve.

Although the catkin was produced for just a few years, the essential elements of the design inspired those of other valve manufacturers.