UU3 UU4 UU5 UU120/350 UU60/250 UU120/500 U10 U12 U14 APV4 DW4-500 DW2 DW4-350 CV1039 CV3760 IW4-350 IW4-500 MU12 MU14 R1 R2 R3 R42 431U 441U 442BU 460BU RECTIFIER VALVE VARIOUS MANUFACTURERS

B4 based HT rectifier valve
Manufacturers: Brimar , Cossor , Ediswan , GEC Valves , Marconi , Mazda , Mullard , Osram , Tungsram
The UU5, introduced during 1935 is in Mazda parlance is an  indirectly-heated HT rectifier with a characteristic envelope shape.   One side of the heater is connected to the cathode.  The anode cavities are each made from two black pressed plates.  This rectifier is designed to work into a maximum reservoir capacitor of 8 µF as is the Tungsram APV4 variant.
 
The UU4 (350V) and UU5 (500V) were used in larger radios from the mid-1930s onward and remained in valve equivalent lists until the 1960s. They were reliable workhorses and many other manufacturers made their own equivalent - just look at the title sequence and you will see possibly the largest range quoted for any valve on this website!
 
Osram had an equivalent with initially, the U14 and the U12 which were the same valve intended to meet all HT requirements up to a maximum of 120 mA at 500V, using a capacitor-input filter but as some valves performed better than others on final factory test the best ones were segregated and marked U14 whilst the lesser performers were marked U12.  The U14 will tolerate a maximum reservoir capacitor of 32 µF and to have an effective series resistance of 100 Ohms. The filament is a thin inverted V ribbon in each of the two anode cavities.

The 442BU is Cossor's iteration and has a pseudo - parallelogram electrode cage just like the yummy 53KU/CV378 and posesses ribbon tape filaments suspended on coil springs - sounds like a description of a Series Landrover doesn't it?
 
The 1821 is the Philips iteration of a B4 based full wave rectifier but as the UU5  has twice it's rating, the UU5 may replace the 1821 but the converse is not advisable - a weedy offering from Philips indeed!.
 
The IW4-500  and IW4-350 are Mullard's pop at a B4 based indirectly heated full wave rectifier designed to work with a maximum reservoir capacitor of 16 µF and a corresponding series resistance of 150 Ohms but showing a maximal voltage ratimg of 500V and 350V @ 125 mA respectively so both are effectively an MU12/UU5 or a R2/UU3 respectively.   For both valves, the cathode is connected to one side of the heater.  For a marginally higher rating as per Osram's U14, the Mullard DW4 series sufficed.
 
Any of these devices make a great main rectifier for PX4 and other vintage valve amplifiers using a B4 valve line up and you can have great fun choosing and tube rolling based on the foibles of these valve ranges as described above.  'Never, in the history of thermionic devices has so much fun been made available through so much choice to a most fortunate few.'   Did Winston really say that.......?
Picture of MARCONI MESH ANODE GLOBE ENVELOPE  1930s U10
MARCONI MESH ANODE GLOBE ENVELOPE 1930s U10
A great rectifier, globe envelope, mesh anodes, Osram, 1930s U10. This device is superb showing full emission when tested on out AVO VCM163 for each diode section. Carries a large maroon Marconi decal as shown.
Stock Code: ex5
Availability: 1 in stock
Delivery date: 1 week
€85.56
Picture of GLOBE ENVELOPE MAZDA UU3
GLOBE ENVELOPE MAZDA UU3
A great rectifier, with chrome, perforated anodes and etched top Mazda markings. This device is superb showing good emission when tested on out AVO VCM163 for each diode section.
Stock Code: G14
Availability: 1 in stock
Delivery date: 1 week
€45.63
Picture of MARCONI BRITISH ARMY MU14
MARCONI BRITISH ARMY MU14
A great rectifier, solid anodes, white British Army Marconi MU14 print. This device is superb showing full emission whn tested on out AVO VCM163 for each diode section.
Stock Code: y25
Availability: 1 in stock
Delivery date: 1 week
€27.38
Picture of AIR MINISTRY VU39 (MU14) MILITARY RECTIFIER
AIR MINISTRY VU39 (MU14) MILITARY RECTIFIER
A great rectifier, solid anodes,Air Ministry VU39 print on envelope and again on base in orange ink. This device is superb showing full emission whn tested on out AVO VCM163 for each diode section.
Stock Code: y22
Availability: 1 in stock
Delivery date: 1 week
€34.22
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