I try to keep the correct original-type tubes in the radios that are on display. So I had been talking about finding the Arcturus made "Crosley" branded, BLUE tubes for my 1931-1932 Crosleys like the Buddy Boy. Most of these tubes have become harder to find than the radios.
Several causes for replacing the original tubes are likely. First - "OH LOOK AT THAT COOL BLUE TUBE" which has a corollary, "I'LL SELL THE BLUE TUBE FOR $$ AND REPLACE IT WITH A CEAR GLASS TYPE" Second, in my opinion, Arcturas tubes were less than average in reliability. The company was very innovative but this did not translate into longevity both in the tubes and the company. So the original "blue" tubes often had to be replaced.
At this point I should explain what a Arcturus "BLUE" tube is, but this site has already done a good job:
Here are 2 "PZ" tubes made by Arcturas and co-branded for Crosley. The PZ was developed prior to the RCA 47 (247) but was similar enough to be used in the same circuits. At some point Arcturas had difficulty sourcing the blue glass, even prior to the conversion to ST shaped bulbs. Pictured on the right is another PZ I already had with a clear G bulb.
Well, while being related to a 42 the PZ is clearly NOT. Besides the base configuration (it wont plug in). a PZ is a relative of the 47 which has a 2.5V filament compared to the 6.3V filament of the 42. No wonder it tested SOOO good.
At some time someone must have tested it as a 42 on a TV-7 since it was marked 90(?)/50, a very high reading and indicative of TV-7 test values. No wonder, it was lucky to have survived the test! I know that this was prior to Harry since he does not have a TV-7. Is seems that nobody even noticed the difference, or the 5-pin base (a 42 has a 6-pin base). The tube required a rejuvenation since the high filament voltage had "paralyzed" the cathode. This brought it up to near new spec.