I've often wondered why Philco used loctal tubes in many of its sets during the 1950s.

I figured it had to be one of the following reasons:

1. Familiarity with using loctal tubes during WW2 in commo gear.
2. One of the engineers had a big concern that the non-loctal tubes would fall out of the sockets.
3. To get around some patent law.

Now, tell me what the real reason was for loctal tubes.

I could be way off base here, but I think they invented them back in the late thirties.

I've seen loctals used in 1940's Sparton and Zenith Radios as well as Philco.

Well, they invented them, they held the patents, they got the royalties on them. So, the more they used them, the more that were made, and the more money Philco got for either making them or licensing others to make them. And, that may have been a little less in royalties they didn't have to pay to RCA too.

The loctal tube developed by Philco was a boon and a bane to radio and television. The good was the design reduced lead inductance and removed the lossy bakelite base hence before the 7 and 9 pin miniature tubes, performed in higher frequency circuits. The bad is that Philco introduced a full range of tubes more or less duplicating the established octal tube range of tubes. This led to an unnecessary proliferation of tube types for many years.

Perhaps the proliferation helped lead to the boon of the publication of tube substitution guides? :yes:

Well, they invented them, they held the patents, they got the royalties on them. So, the more they used them, the more that were made, and the more money Philco got for either making them or licensing others to make them. And, that may have been a little less in royalties they didn't have to pay to RCA too.

Did you ever notice that Philco , never used metal tubes or tuning eye tubes.
They were the last firm to switch to octal based tubes. When they did, the tube shield bases restricted the use of anything but the "G" types. How many Philco radios did you run across, that had the bases butchered to use a larger diameter replacement tube?
They were the only firm to use UX based tubes, as late as the 1942 model year, even in Military equipment.

I always figured that they were trying to use up the over abundance produced during the war.