| Author | Message | ||
| Jacob Jaffe (wordsandsigns) Username: wordsandsigns Registered: 01-2009 |
I recently (a month ago) bought a used 112-65. The guy I bought it from didn't really use it much - he had never changed the tubes and didn't know if they had ever been changed. Yesterday I was playing through it and trying to get some power amp distortion (master volume was on 10, channel volume at about 3), when the sound cut out. A little after I lost signal I turned around and saw a lot of flashing light coming from the back of my amp, followed by the smell of something burning. I unplugged my amp, and traced the smell to one of the power tubes. I took it out and there are burn marks on terminals 2 and 3 of the tube. I figured that I was going to have to replace the tubes but I also want to be sure that nothing else is wrong with the amp, eg. a blown fuse, cap or resistor. Also, the tubes that were in the amp when I bought it are not marked very much... the only markings on them are "Xf4 B6J4" at the bottom of the front of the tubes. The amp calls for EL34s or 6CA7s, so I was planning on picking up a pair of those and rebiasing my amp to work for them, but what kind of tubes are in it now? I did a little searching and nothing came up, except on http://www.vacuumtubesinc.com/audionew.h tml this site, where they are listed as 6EU7 type tubes. I'm hoping I just blew a tube and need to replace them, but I'm not sure! Any and all help is appreciated, thanks! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Sorry-haven't been in much. You need to ID WHICH amp you have first. With 12ax7 or without and the like. Then you are going to have to open the chassi up and see if you burnt the resistors around the plate circuit(on the sockets). If the tubes went chernobyl on you, chances are you torched the plate resistors or SOMETHING. You never know, somebody OCULD have put the wrong tubes in there to. REAL 6CA7's are ungawdly expensive, IF yo can even find them.. You'll probably want to get E34L's. I suggest JJ's, simply because I get the best service out of them. The Winged C are good to. If it HAS a bias circuit(with 12ax7) I suggest firing it up WITHOUT power tubes first and measuring the control grid voltage first to make sure you HAVE some and enough to control the tubes. ALSO, re-tension the sockets so the tha bias control voltage is GETTING to the tubes. Lastly, BE CAREFUL. Almost 700v on those plates. Let us know if we can help. |
Tue, 03/25/2014 - 09:32
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