THE GREAT MULLARD MAGIC BLOG — leak tl12.1

Today, a question from South Korea - what is the best Mullard input valve for a Leak TL12.1.  Well, you can fit as per original, the EF36 or the improved version, the EF37 or the super improved version the EF37A or the mega special version the ME1400.   The Mullard Type EF36 was designed and introduced to market in 1940 as a general-purpose RF/IF/AF pentode with a non variable mu characteristic.    There were two famous uses for the EF36, firstly, Colossus, Tommy Flower's computer at Bletchley Park used rows n rows of them then of course in 1947 the Leak TL12.1...