This month I am presenting a tube which I had in mind for this series since a long time. Whenever I came across my small stash of these I told myself to write about them. Now the time has come, here is the 53.
bottle) while the 6N7 was also made in straight sided glass and as metal type. I have never actually used the 53 but there is no reason why it shouldn't perform as well as the 6A6 or 6N7. Probably due to it's ancient heater voltage spec of 2.5V it is largely ignored by audio amplifier designers who prefer to stick to the standard 6.3V types. I am guilty myself for not using it for the very same reason. So it is still available at modest prices and easy to find. Since I never used it in any of my designs I only acquired a small stock of them. As usual, let's have a look at the plate curves in the data sheet and at actual curves taken by a curve tracer. Most data sheets I have seen don't even bother to show a set of plate curves for the 53 but only have a common diagram for all the three types:
The UX7 base:
The old leaf logo on the base:
These allow extra cooling of the grids which are driven positive in Class B circuits.
A close up showing the heater wires going into the cathodes:
Philco branded 53:
I tested the tube and it came out fine with maybe the transconductance a bit low but still within acceptable limits.
Next we have a Ken-Rad 53:
Like many Ken-Rad tubes this also has the characteristic black coating on the glass.
And lastly National Union:
These have the getter applied in the top.
Like the 6A6 the 53 does not give off much light when powered up:
I hope you enjoyed this first tube of the month post of 2018!