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The valve as it arrived at the museum. Part of the envelope was detached but the electrodes had not been crushed.
Bob Kars kindly donated this CV490 to the museum but sadly it was damaged in transit. However, that damage gives an opportunity to explore the construction in more detail. Our CV490 exhibits can be found here and here. The CV490 was the UK Government specification for the commercial 19H5 high power rectifier.
Above the 9 looks to be the point of impact that broke the glass.
The first thing to remove was the top cap. Using electronics side cutters the rod passing through the envelope was the point of detachment. However the rod was exceptionally hard and the side cutter broke - with little damage to the rod. The soft wire below the rod was then cut.
Top cap with cement filling the plastic cover.
The soft connecting wire to the anode is welded to the top cap rod.
Top view with top cap removed.
With the top cap removed the four section anode can be clearly seen. The vertical oxide coated filament wires are all connected in parallel. The U shaped channel that holds the supports for the filament is supported on the two ceramic rods and the pair of vertical rods in the centre. The pairs of filaments are wired in parallel at the base and joined together by the top supports, thus making a series connection of the two parallel pairs.
Each section of the anode is formed into a cylinder with the filament placed centrally with space between it and the walls as the voltages employed are large.
The main parts of the glass remain in place.
A closer view reveals the inner joining plates. These are welded to the outer edges of the anodes.
The wings welded to the side of the support that joins the anodes are present to hold the structure firm against the glass. By the left wing is the point of attachment of the soft wire linking the anode to the top cap.
Filament.
The four filament wires are oxide coated and welded to the top support bar. The anode plate has been pressed into shape and welded at the seams.
With the glass removed.
The pinch.
The main assembly is held firm at the base by a collar round the pinch stem. The ceramic tubes that support the tops of the filaments are set into cups attached to the support collar. The lower filament connection is made via a spring wire to maintain tension.
Tension springs.
In the above image each pair of filaments is held by a spring wire welded to the support fixed into the pinch
One anode pair.
The central filament support rods can be seen to be set into glass at the base and welded to the U channel at the top.
 
The strap connecting the anodes passes either side of the ceramic rod. The strap is not clamped to the ceramic leaving the anodes room to slide a millimetre or two.
Anode joining strap.
The lower end of the filaments. The filament ends are joined to the springs and around them are wire loops - possibly to stop a complete short if one filament breaks. The four pressed and joined anode plates. Note the cups formed in the anode that are used to hold the top bridging wire.
The Goliath Ediswan Screw base hides the evacuation seal. The collar is secured around the pinch stem with two nuts and bolts. to the right is the cup that originally held the getter material.
The pinch stem.
Dimensions
- Anode: 60 mm × 38 mm. The cylinder section is 13 mm in diameter. The outer joining straps are 28 mm in length and 20 mm top to bottom. The inner plates are 22 mm top to bottom.
- Filament: 0.42 mm diameter and 83 mm long (each strand).
- Stem: The pinch stem is 25 mm in diameter.
- Ceramic Rods: These are 4.0 mm in diameter and 108 mm in length.
- GES: The base cap is 53 mm in diameter and 60 mm top to bottom. The thread is 39 mm in diameter. The lower connection is 18 mm in diameter and separated from the thread by ceramic insulation.
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