Summary

Two small output triodes. The PM 4 was the first of the PM (Philips-Mullard) series to be released in 1925. 4 volt directly heated cathode.

Physical Description

Intact valve: conical glass bulb. American style 4 pin (UX) base with Bakelite shell mounted on display block with a sectioned valve of the same type ST 021572.2. Sectioned valve: conical glass bulb mostly removed to show horizontally mounted rectangular electrode structure mounted on a glass pinch. American style 4 pin (UX) base with Bakelite shell mounted on display block with an intact valve of the same type ST 021572.1.

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