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Friday, January 29, 2021

Tube of the Month : The 6V3


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.

As far as I am aware the 6V3 (later released with an 'A' suffix) is the only miniature TV Damper tube. The pinout of the Noval base is shown on the left. The heater is connected to pins 4 and 5 which is common for 9 pin tubes. The plate is connected to pins 2, 7 and 9 while the cathode is brought out to a small top cap. The latter is obviously done since the high voltages which occur in TV Damper tubes would arc across the narrowly spaced base pins. The heater consumes a hefty 1.75A at 6.3V. Quite a lot for a tube in such a small bottle. The maximum DC plate current is 135mA (800mA peak) and the maximum inverse voltage is 6kV. Somewhat similar to other TV Dampers like the 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. 

Let's go through my collection of 6V3 tubes.

Here we have 6V3As made by Sylvania.

A close up to the top where we see the isolation spiral between heater and cathode which ensures the high voltage ratings:

Another Sylvania which came in plan military packaging:

DuMont branded 6V3A:

DuMont obviously sourced their 6V3s from Sylvania as they share the same construction style:



This one has a quite elaborate construction with 3 mica discs.

Some close ups:


Identical construction to the Raytheon above, but not sure who cross-branded whose tubes:

IEC Servicemaster 6V3 made by Mullard?

And lastly General Electric 6V3A:

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:

A spiral of wire wound around an insulated center piece.

The cathode:

Quite massive for such a small tube!

The plate with massive cooling fins:

An interesting tube with surprising manufacturing details. Makes me want to use 6V3s in a project!

Closing the post with the tube lit up.

Best regards