The Loewe HF2 double valve.
A correspondent reminds me that one of the reasons for the production of two-in-one and three-in-one valves in the mid nine-teen-twenties was the queer royalty system Ior wireless sets which then prevailed. He is quite right: I had clean forgotten what was perhaps the main reason why, in its early days, popular wireless reception developed along such different lines here and in the USA.
Any British set that you bought had to add to its price a royalty of so much per valve holder. Motor cars were handicapped in much the same way by the horse-power tax. Neither of these things obtained in America. Over there cars rated at 20-30 horse-power were the popular models. Here manufacturers strove to get the last ounce out of small engines. Similarly, quite early American domestic receivers contained numerous valves, whilst two or three, all working fit to bust, were for a long time the rule here.
Then the Loewe Company had the brilliant idea of fitting two or more electrode assemblies, with coupling resistances and capacitors, all into one gigantic bulb which could be inserted into a single holder. Later we continued to suffer badly from the same few valve-holder complex, even when this form of royalty had gone: we designed valves with slopes like the side of a house and continued to work them all out: seldom, in fact, can so much have been done for so many by so few.
Later still we went all complex-valve minded, largely because the ordinary man was afraid of the expensive replacements that might be needed if he bought a set containing more than four valves, excluding the rectifier.
I hope sincerely that after the war we shall enter an era of bigger and better sets, containing simpler valves and more of them.