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Hi,I pulled a bunch of 12AU7A RCA Cleartops from the tone generator unit of an old Conn organ this afternoon. They all have a thin layer of grime on the glass so I took one tube and ran it under some warm water. I then wiped it with a soft rag and off came the printing. The 12AU7A didn't come off because I assume it's etched on but the orange CONN, MADE IN USA is gone. Personally I think that the orange CONN is ugly but I guess my question is, "Is there a way to clean these tubes without wiping off the printing?"
Follow Ups:
They're just too dirty to try to work around the printing not to mention that the ink smears fairly easily just by holding the tubes tightly to insert and pull them from the sockets so will someone please correct me if the following statement is incorrect..RCA cleartops have 12AU7A etched on the glass. They have "D" shaped side getters with grey plates. No one else ever manufactured a 12AU7A that can be mistaken for an RCA cleartop.
Yes, the print is very fragile and comes off very easily. Some printing is etched into the glass. What ever method you choose to use to clean the glass and the pins you'll want to work around any printing if you want to keep it. I do prefer to keep the print whenever possible myself.
They're glass....right? So glass cleaner is what you need. I like to use Q-tips wetted with Windex. Be very careful around the lettering or just leave that part untouched.
Use 0000 steel wool and gently swipe the tube - small areas at a time, avoiding the numbers (you can get right up next to them). Spray a bit of WD-40 on the wool for stubborn areas. You can clean the bakelite areas and pins with the wool too. Take your time and end up with a new looking tube. Too bad they do not end up testing new afterwards...
you said - "Too bad they do not end up testing new afterwards..."It's funny that you mention that because there are 27 of them and they all test as new on my tester. My tester doesn't have the ability to test the individual triodes so it sums the two halves. The standard transconductance of one triode is 2,200 MicroMhos so the summed reading should be 4,400 MicroMhos for a new tube. Yah, I know this isn't the best tester for dual triodes but the bottom line is that there are 27 tubes and they all test between 4,700 and 4,950. This tester has indeed picked out other bad tubes as was evidenced by how they sounded, or didn't sound, in my preamp and subsequent tossing of bad ones into the trash can. I'm guessing that since they were used in the tone generation section of the organ that they just weren't used anywhere near their maximum capacity. I don't know. Any ideas?
Hi Bob ,
Testing both sections at once is not a good idea , after all one section could test 150% and the other 50% ! Ever thought about making an adapter with a plate switch ?
Oh, oh! I think that ain't right, FB. I am going to guess our fellow Bob owns a B&K 500. They tell you in the manual that the combined transconductance is 'carefully' calculated for. If the one section is at 150% of gm, it is probably leaky or gassy. The 'Shorts' test or the 'Gas' test would show that. Besides; having one section 'gassy' is probably impossible. I can't recall if the B&K 500 has a 'Life' test, but a triode at only 50% of gm wouldn't pass a 'Life' test, either. These are all guesses; I may be full of crap.
and it tests for shorts, combined transconductance, life and gas.
All of the cleartops tested great on it but the best test available to me is when I try them two by two in my Foreplay preamp. The Foreplay has separate volume controls for left and right and has a very thin top chasis plate which means that microphonic tubes will be easily identifiable.This is kind of fun, maybe I'll run an ad in the local paper:
"Old tubed ogans hauled off for $10." :-)
fatbottle,"Ever thought about making an adapter with a plate switch ?"
Nope! But now you got me thinking. I'll go to Duncan Amps tube data page for a 12AU7 and print it and get out the pencil. If I can figure it out it will sure be cheaper than looking for a better tester.
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