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The envelope carries only one readable word 'Audion' but the box it came in was labeled as High-Mu. With the filament open circuit we can only rely on the box as the correct identification.
The attached PDF file shows the three types of valve made my Myers in the early 1920s. Myers had worked with De Forest, RCA etc. making valves and infringing patents along the way. Technically his products were good and performed well. The HI-MU had a higher amplification than his other two designs the Universal and the Dry Battery.
The Canadian valves had an M on the end caps. This earlier American valve just has plain ends.
The construction uses glass beads to hold the electrodes rigid. The filament connects between the two ends. The anode goes to red end and the control grid to the black end. In the image the filament connections ar at the top.
With the valve turned over the filament is at the bottob. The end of the filament can be seen on the left in the fold of the support.
The folded anode spot welded to the upper support. The left hand supports: upper - the end of the grid helix is retained in the fold of the support, lower - the filament termination.
A closer view of the black end.
The red end with the filament connection in the centre. The grid support goes into the glass bead but does not connect to the base pin.
Thanks to Louis Vermond for alerting me to this valve on ebay.
The thin glass tube envelope is 16 mm in diameter, and including the base pins is 86 mm tall.
References: Data-sheet & 1047. Type HI-MU was first introduced in 1920. See also 1920 adverts.


Absolute Maximum Operating Conditions
-1 to -10
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated September 28, 2017.
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