Stan had a few 7242's. He wanted some stupid money for them when I first asked about them. About 10 years later he had not sold any but would not accept less than $100 each so I never got to play with them.
Visit your local ham fest if you get a hankering for this sort of thing. I have seen lots of good deals at my local ham fest. Or look for estate sales of departed hoarders who do not have a good exit plan.
6336 and 6528 V regulator tubes have 2 triode tube sections, identical to the 7241 and 7242 sections respectively, which have 3 of those sections. They also allow use as two separate tubes, while the 7241 and 7242 only allow all three sections in parallel (at least for the plate, which could still be used separately for V regulators off the same B+ I guess. ) 6336 and 6528 are a LOT cheaper though, and octal.
Use a 12v car battery charger to get it going
You can use a 50A bridge diode to isolate the supply.
Start it with the charger turn on the supply after it is at 12v
You can use a 50A bridge diode to isolate the supply.
Start it with the charger turn on the supply after it is at 12v
I got the 7241 tube to heat up finally using the big Xantrex supply and heavy duty wires. However the heater current stays at 10.8 Amp indefinitely at 6.3V on the tube heater pins. Supposed to be 7.5 Amps. This made me suspicious, too much heat conduction. Can hardly see any red glow on the heaters. So I put 50 V across the cathode to plate pins with grid1 tied to cathode. This put 5 mA thru the tube with a bright purple glow. Confirming my suspicion that it has air in it. Going to send it back. Looks like I'll be staying with 6528 and 6336 tubes ( new ones ).
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Both of those were pretty common in military surplus back in the 70's and 80's. I still have some of both varying in condition from crusty and ugly to nice, and a few still live in their original boxes.
I used them for the cathode follower output stage in the amp I designed for the Circuit Cellar Magazine article back in 2007. It was driven by a typical two stage SET using a 6EM7 with a CCS load instead of an OPT to develop the huge drive voltage needed for the CF output stage. I think I used 6AS7GA's for the magazine pictures because they were new and shiny, but I really wanted the 7242 because it just looked bigger and better.
