Quote:
Originally Posted by turretslug
My understanding of the 6X5/EZ35 early adoption of 6.3V and isolated heater/cathode was for car radio power pack use- but that's both hazy and tenuous!
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There’s evidence to place that assertion in the probable or very probable class, namely this excerpt from the article “Miniature Tubes in War and Peace” in RCA Review for 1947 June (available at AmericanRadioHistory.com):
At that time, miniature rectifiers were not offered for use in for use in AC mains-operated domestic receivers, but were offered for auto radios (the 6X5) and for AC-DC and three-way portable receivers.
An interesting facet is that when the US auto industry made a general change from 6-volt to 12-volt electrical systems in the early 1950s, there was also a change from 6.3 volt to 12.6-volt heater valves doe auto radios. Many such valves already existed; for example, quite a few of the 150-mA series-string heater small-signal miniatures happened to have 12.6-volt heaters. But as required, there were new issues starting from late in 1952 or thereabouts.
Returning to the 4-volt case, there were post-WWII new equipment designs that used them. The Dynatron T69 and associated range comes to mind; it used Mazda 4-volt valves. Dynatron switched to Osram miniatures for small-signal functions circa 1951 with the T99 and associated.
There were also one or two post-WWII new-issue 4-volt valves. The Philips AZ41 comes to mind, from its initial Rimlock series. It was a directly-heated, 70 mA full-wave rectifier.
Cheers,