I'm not really sure if these are a family of valves or not, but as several different types of British valves with B7 bases and 13V indirect heaters were produced I thought I'd list those I know of here. These valves tend to be described as for series heater use in chains of 200mA or 300mA depending on the type, they are also described as suitable for use with 12V car batteries. They seem to be variants of valves that exist with other bases and other heaters (26V and 4V), some are Catkin types.
One interesting point about these valves is that they seem to show the early British valves with their 4V 1A heaters (i.e. 4W) start a chain of developments that lead to 6.3V types in USA. A problem with 4V heaters was hum resulting from the high current - the data sheet for the H30 triode remarks in it's low residual hum.
Several of these valves are listed as used for ship transmitters and receivers in the 7th edition of Handbook of Technical Instruction for Wireless Telegraphists (Dowsett, 1942). Which suggests they were in use during WWII. A scan of the relevant page is attached here.
Octal base types with centre-tapped 26V heaters, i.e. can also be used at 13V include Osram KT33C and KT35 output tetrodes.
There's a very interesting description of a 1934 (or perhaps 1933) GEC wireless using some of these valves at http://www.classicwireless.btinternet.co.uk/gecd.htm
The service sheet for this set is available at http://www.radiomanuals.info/information/Broadcasters/sGEC%20AVC.pdf