The TF2604 was a further development of the TF1041 series of valve voltmeters, an example of which is shown elsewhere on these pages.

The changes from the TF1041 series were mainly cosmetic, however some minor circuit and component changes were also incorporated.

The TF2604 uses thermionic valves for most of its operation, although a transistor stabiliser circuit is used to provide a DC regulated supply for some of the valve heaters, thereby improving stability against mains supply variations and reducing the effects of mains "hum".

It features DC and AC voltage ranges (to 500 MHz or thereabouts) in addition to a resistance measurement facility. A circuit diagram can be found below.

This example is in good working order.