History of Science Museum: Collection Database Search

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The MH4 indirectly heated amplifier triode is of unusual internal construction. The cathode assembly passes through the far end of an oval grid. The grid is fixed only at the outer end to a stout single rod. The anode is a thin sheet and is open at the front of the grid support. The channel formed by the anode sheet encloses the cathode and the far end of the grid. This method was known as Shortpath Construction. The MH4 is identical in construction to the landmark Mazda Type AC/HL long-life valve which was introduced in the 1930s and continued in use until the 1960s.

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