Our first 15 Broadcast pedals came fitted with an NOS Mullard-made CV5712 Germanium transistor. We received a few messages about these CV series transistors so here is some additional information on these transistors.
The CV series of semi-conductors (diodes / transistors) and tubes were manufactured and specifically labelled for use by the UK military. These UK inter-service military specification devices were manufactured by the likes of Mullard, Philips, Valvo and Newmarket but usually are not printed with the manufacture’s name.
Each device normally is printed with its model number, for example CV5712, followed by a series of letters and numbers. These letters and numbers can be used to determine where the part was made and when.
Many CV series devices have an equivalent commercial device for example the CV5712 is equivalent to the more common OC71. It is thought that a high number of CV devices were standard commercial devices but manufactured to tighter parameters and high tolerances. From experience testing these devices, I tend to agree with this. Whilst the CV transistors don’t out perform their commercial cousins, readings I took from various batches of the CV devices do tend be much more closely grouped than the standard commercial devices; though this may only hold true for the the batches I’ve been able to test.
You can look up CV equivalent devices on the CV REGISTER.
The next set of letters usually starts KB, though these are sometimes not present –
especially on later devices. The K means that it has been manufactured to specification and the B indicates that approval was given by UK authorities. The next letter or letters is the FACTORY IDENTIFICATION CODE and denote/s which factory the device was manufactured in.
FACTORY IDENTIFICATION CODES
D – Mullard, Mitcham
NQ – Texas Instruments, Bedford
RC – Ferranti, Chadderton, Oldham
NTN – Newmarket
WE – ASM Ltd, Broadstone ( ASM was a joint venture between Mullard and GEC, and the code WE really designates a GEC factory that pre-dated ASM)
More examples of Factory Identification Codes can be found here.
The final four numbers denote the date of manufacture of the device. The first pair of numbers denote the year of manufacture and the secound pair which week with the year the device was built. For example a device printed with 6428 was manufactured in the 28th week of 1964.
More reading and information can be found on the wonderful Mister Transistor’s Vintage Technology Pages