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PX25

Sensibly equivalent to:
CV1040 DO24 NR47 P27-500 PP5/400 PP6/400 VR40
See also:
Osram Advert, December 1947 - Stabilized Power Supplies - Valves in PA Equipment - The Williamson Amplifier - Osram KT2, KT76, KT33C, KT66, KT61, KT66, PX4 & PX25 Advert - Osram PX4, PX25 & KT66 Advert - Osram Valve Range Advert - Hartley Turner GA12S Amplifier
    
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The PX25 is one of the all time classic audio output triodes. This example is branded as an Osram product as can be seen below, note also the hand construction with the band held against the pinch.
The PX25 is directly heated and feeding the filament to minimise hum is not straight forward. Williamson, who worked for M-OV and then Ferranti, indicated that the modern indirectly heated KT66 when strapped as a triode was almost identical in performance to the PX25.
The Osram brand is etched into the glass. The four support struts fitted to a collar around the pinch stem was introduced in the LS6A that became the PX25.
The Type designation is etched into the dome of the envelope.
Unlike the earlier LS6S that had coated filament ribbon the PX25 has four hairpin filaments of coated wire.
The balloon envelope has a maximum diameter of 65 mm and excluding the B4 base pins it is 144 mm tall.
References: Datasheet, 1005 & 1043. Type PX25 was first introduced in 1932.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
Pdiss
D
4.0
2.0
500
-54
82
26
4%
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated August 01, 2015.
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