MH4, MH41, 41MH, HLA1, AC2/HL, 904V, 4DXAC, VR505, SMALL SIGNAL, B5

The MH41 is a mains triode that has the 1930s UK standard 4 Volt 1 Amp heater. The valve is a low impedance device and designed for audio frequencies.

The MH41 is essentially an uprated MH4 and was M-OV's response to the Mullard Type 994V as a high-gain detector triode. Unfortunately, by the time the MH41 hit the market the real need for modern superhets was for double-diode-triodes such as the MHD4.

However, the MH41 saw service as an audio pre-amplifier and in professional applications where a redesign was soon implemented to reduce intrinsic hum levels following a BBC complaint.

Some devices have a mesh anode to reduce the risk of interstitial gas entrapment in manufacture.