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ID = 15284
Great Britain (UK)
Brand: Cossor, A.C.; London
Tube type:  Triode, vacuum   Power/Output 
Identical to 41MP = YN4 = CV1458
Similar Tubes
Normally replaceable-slightly different:
  104V ; ML4
First Source (s)
1929 : History of the British Radio Valve to 1940 p.173 & 180

Base Europe 5-Pin , B5 (Eu O, F, O5A) 1928 (Codex=F)
Was used by Radio/TV-reception etc.
Filament Vf 4 Volts / If 1 Ampere / Indirect / Specified voltage AC/DC

Constructed as tetrode with 2 grids. Grid # 2 is connected to the anode rod via a spiralised resistor wire.

Text in other languages (may differ)
Information source Babani, International Radio Tube Encyclopaedia   p. 24 & 25
Taschenbuch zum Röhren-Codex 1948/49   

7_56.png 41MP: Telefunken Werkstattbuch
Wolfgang Bauer

Just Qvigstad
Usage in Models 1= 1928? ; 1= 1931? ; 1= 1931 ; 3= 1932 ; 1= 1933?? ; 4= 1933 ; 1= 1934 ; 3= 1935 ; 1= 1936 ; 1= 1937? ; 2= 1937 ; 2= 1938

Quantity of Models at with this tube (valve, valves, valvola, valvole, válvula, lampe):21

Collection of



Forum contributions about this tube
Threads: 1 | Posts: 7
Hits: 2178     Replies: 6
41MP, triode connected tetrode, please explain
Nicolaas van Dijk

I have a 41MP triode, but looking at the interior, it is a tetriode. The second grid is internally connected to the anode via a small spiral. may be just to prevent mechanical stress or it may be a resistance. Can anybody tell me what the reason is for this construction?


Wolfgang Holtmann

You are right, the second grid is tied to the anode.

Here is the explanation by the manufacturer:

In fact, with this trick the anode get's closer to the control grid and the claimed Mutual Conductance
of 7.5 mA/V is achieved.


Kind regards.


Jacob Roschy

I don't understand what's the advantage to mount a second grid close to the control grid and tie it to the anode, then mount the anode itself just as close to the control grid ?

Best Regards,


Dietmar Rudolph † 6.1.22

The advantage of this construction may be threefold.

  1. No new design for trode or tetrode is necessary.
  2. Reduced capacity between grid and anode unlike a triode having its anode in the distance of the 2nd. grid.
  3. Heat dissipation can be increased while the first grid stays cooler.

Best regards,


Nicolaas van Dijk

Dear Dietmar

I respomd to you, but really like to thank all of you for the answer. The reasons seem clear and indeed, the valve has a very high transconductance. Perhaps I like to try the 41MP one day in an amp to see how it behaves, interesting


Wolfgang Holtmann

Another advantage -due to the high Mutual Conductance- an additional lf-preamplifier may be obsolete.

On the other hand,
as already stated in the Manufacturers Info, no large output can be obtained.

The reason for this is given in the Technical Data below:

Because of the little distance of the second grid (at anode level) in respect to the control grid, the anode voltage is limited to 200 volts!

Kind regards

Jacob Roschy

Since this design was not continued in newer types, it may not have fulfilled as was expected. As only 12 models used this tube, it could be considered as a non-starter.

The reduced capacity between grid and anode may not be of much importance for an audio output triode.

While the heat dissipation of the anode can be increased, the thin windings of grid # 2 are even more endangered for overheating, hence grid # 2 is connected to the anode via a spiralised resistor wire as current limiter.

Best Regards,



End of forum contributions about this tube

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