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Information - Help 
ID = 2829
United States of America (USA)
Tube type:  Triode, vacuum   Audio Frequency 
  Ca. 1925 up to 1945 rare.
Identical to 201B = UX-201B = X201B

Base UX-Base (4 Pins (2 thick, USA 1924, UX) (Codex=Bo)
Was used by Radio/TV-reception etc.
Filament Vf 5 Volts / If 0.125 Ampere / Direct / Battery =
Description Thoriated-tungsten filament version of 201/UX-201, with reduced current drain. This particular tube has a De Forest-Crosley label, but is made by Westinghouse Canada. 
Dimensions (WHD)
incl. pins / tip
44 x 112 x 35 mm / 1.73 x 4.41 x 1.38 inch
Information source Saga of the Vacuum Tube, Tyne   p.101
Taschenbuch zum Röhren-Codex 1948/49   
Tube Lore (I)
-- Collector info (Sammler)
201B: own collection
Peter den Boer

201B: ARRL Handbook 1972
Michael Schlör


from Just Qvigstad

Usage in Models 3= 1925 ; 1= 1926

Quantity of Models at with this tube (valve, valves, valvola, valvole, válvula, lampe):4

Forum contributions about this tube
Threads: 1 | Posts: 7
Hits: 2243     Replies: 6
201B (201B)
Robert Weaver

This type is incorrectly shown as having a 1.5 volt 1.0 ampere filament. This tube is essentially the same as type '01A but with lower current filament.

Correct info:

Filament voltage: 5.0 V

Filament current: 125 mA

Information from manufacturer's package (see attachment).


Emilio Ciardiello

Many thanks, Robert. This agrees with data given by Lud Sibley in 'Tube Lore'.


Robert Weaver

Hello Emilio,

The filament voltage is still incorrect. It should be 5 volts.

Best regards,


Emilio Ciardiello


of course you are right. I missed the editing of the voltage value.

Thanks again,


Jacob Roschy

If the 201B has 5 Volts heater voltage, I wonder how the type 26 can be “Normally replaceable-slightly different”, when its heater voltage is 1.5 V ?

Which are now the heater ratings for the “Other base” types CW-186 and 201A_Western ?

Best Regards, Jacob  

Emilio Ciardiello

Good question, Jacob, but any action is very difficult on early tubes. According to Sibley, the WE 201A, and hence the CW-186, is unrelated at all to UX-201A. Always referring to 'Tube Lore' by Sibley, the 201B in this topic should be more correctly referred to as UX-201B. This was the evolution of the UX-201A, thoriated-tungsten filament drawing 250mA. The same UX-201A derived from an elder UX-201, pure tungsten filament requiring 1A, that was a rebased UV-201. Sibley also reports a tipped Westinghouse variant of UX-201, labeled as RCA Radiotron, with filament requiring 4V at 800mA.

The RMorg archives do not lists some of these variants. What is worse is that, once entered the missing codes, all the cross-links to equivalent types by other manufacturers are to be checked and probabily changed. And even worse is to check each one of the cross links relating each tube to the several radio sets.

Any good idea to solve this fix?


Jacob Roschy

Dear Emilio,

apparently these cross-links to WE201A and the CW-186 were taken from unreliable sources and should be removed as cross links, at least until we get better information.
If the 201B is fully identical to the UX-201B in the same way as the 201A is identical to the UX-201A , then we should register the UX-201A and cross-link it to the 201B.

Since tubes of this vintage are not in the center of my interest, there is little I know about them.
Anyone who knows more may be encouraged to contribute.

Best Regards, Jacob

End of forum contributions about this tube

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