In last months Tube of the Month post about the 5687 I mentioned that not many 9 pin miniature (Noval) tubes have been covered in this series. So I decided to pick another Noval tube for this month. Meet the 6V3.
Since TV Dampers are among my favourite vacuum tubes I looked through my tube storage and found some 9 pin specimens.6AX4. For the complete technical data refer to tech RCA data sheet. And for some technical background on TV dampers see the 6AU4 post. Like other TV Dampers the 6V3 and 6V3A could be used as rectifier in power supplies.
DuMont branded 6V3A:
DuMont obviously sourced their 6V3s from Sylvania as they share the same construction style:
I salvaged this one to have a look at the internal construction:
This tube has a peculiar detail which I have not seen before, a small metal disc mounted below the cathode:
Probably as a measure to prevent arcing?
Here we see that the upper mica disc centered the heating element in the cathode while the second disc holds the cathode in place to ensure distance to the plate.
Here we have a better look to the small disc at the bottom which is connected to one of the unused pins (nr 3).
Not all the 6V3 have this feature. Only the Raytheon and General Electric. If anyone knows exactly the purpose of this disc, please share.
Another surprise detail I have not come across before is the construction of the heater element: