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DET5 was made by Marconi, and is a directly heated triode with balloon
shape. It is said to be an equivalent of the British military NT40.
NT40 is said to be equal to PX-25, except it is rated for 600 volts
due to higher vacuum.
The glass bulb is thick and weight almost 50% more than PX-25. On the
glass is etched Made in Bohemia, which I assume means the glass work
is made there as the Bohemians managed to obtain a higher vacuum.
If it is a PX-25 with higher vacuum it must be a perfect output tube
in a single ended amplifier!
Does anybody have complete data for this scarce tube? I have a few and
want to try it in my amp.