The R.4 was a hard vacuum valve developed from the R Type to meet a specific need for a heterodyne receiver. See the article above for full details. See alsoR2 and R5.
The lettering on the envelope reads: Valve wireless receiving R.4 Patt. No. 4411. A8971. The other side reads: Osram GEC Made in England. R.4. The lettering reads top to bottom when the envelope is screwed into the screw holder. The R Type standard of the pinch above the base became dominant.
The envelope has text etched on both sides. The identification of make is Osram.
Before the B4 base became a standard the connections were referred to as caps. Here we see the candelabra cap. This is in fact a Medium Edison Screw (MES) cap that we normally associate with torch bulbs. The cap covers the evacuation tube.
The connection leads emerge from the pinch. The grid and anode are left as flying leads. The filament twisted copper wires are soldered to the cap. In this exhibit the filament leads are detached from the cap.
The construction of the anode and supports are very clearly based on the early R valve pattern.
Here it can be seen that the tungsten filament is still connected to both end supports.
The anode, twisted wire grid supports, pinch and filament supports.
Close-up of the fixing method for both filament wire and grid. The grid helix is fixed to the single support rod at each turn. The main support rod is augmented by a thinner wire that winds around the grid wire and holds it in place against the main support. The wire is corroded - possibly a sign of a failed vacuum.
Both ends of the filament and grid. The grid wire, support rod and holding wire can easily be seen on the left of the anode.
The R4 came in this cardboard box. This valve was designed for a military application and not a consumer product and so the box is entirely functional.
The letters D and E can be seen on the right. This suggests that the box was not the original for the R.4.
The balloon envelope is 50 mm in diameter, and including the candelabra cap is 86 mm tall.
References: 1003 & 1004. Type R.4 was first introduced in 1917.