The Noval base (miniature 9 pin) tubes are somewhat underrepresented in this series. Less than 10 covered so far. So let's pick one for this month. Meet the 5687.
The 5687 is a double triode wich was designed as a general purpose tube. Both triode systems are identical and are of the medium mu variety.
data sheet. Quite remarkable why it fell a bit out of fashion. But I admit I myself ignored this tube so far. But maybe this will change sometime in the future. Since I never used this tube type I do not have many samples, only 10 pieces and all of them are made by the same manufacturer. As always let's have a look at the plate curves first. Here the set of curves from the data sheet:
And the measured curves:
All the 5687 I have are made by Philips ECG (formerly Sylvania):
The 5687 was intended for industrial use. Industrial tubes were given a 4 digit type number. The prefix JAN on the tubes shown stands for Joint Army Navy. So these had been manufactured for the military.
They were packed in the typical plain white boxes of the military. The date code indicates these have been made in the 1980ies. Although the date on the box is a packed date and not necessarily the manufacture date of the tube. But it is most likely the tubes had been made around the same time.
The W-suffix indicates a ruggedised type and the B-suffix a revision in maximum ratings or some other specs. But I did not find any information about what has been changed in the B-version.
Enjoy some views of the tube from all angles.
Some close ups:
Quite an impressive little gem!