[ARC5] 7V and 14V Tubes

[Kenneth G. Gordon]

On 30 Apr 2012 at 17:59, J. Forster wrote:

> That logic explains the need for a separate transformer winding, but
> not the 5 Volts.
> 
> Having a few hundred volts between the heater and cathode of a tube
> can lead to failures...  big time. Viz. the AC power supply for the
> Cabadian WS19. A 6X4 failure often destroys the unobtanium power
> transformer.

I suggest that the 5 V tubes came about during the time that most tubes had 
2.5 V filaments. 2.5 X 2 = 5.0.

There is probably some historical reason for it, rather than a technical 
reason.

Ludwell Sibley's book may tell us.

Ken W7EKB