Bob Womack
Well-known member
- Joined
- Apr 8, 2002
- Messages
- 2,197
Well, this is a first for me. I was playing along merrily today, at bedroom volume, when my twenty-year-old JTM60 went HUMMMM... Click.. and silence. I know, I know, these are known to overheat and no-one likes them but this one has been great for me. I use it mostly at the studio.
Power light still on but I shut her down immediately and let her cool. The fuse is good. The trannies look pristine, no color or leakage. No smell and I didn't let the smoke out. I opened up the tube cage and checked the original 1996 Huntsville/Petrograd Svetlana EL34s that are set horizontally at the bottom of this chassis. No carbon trace on the pins. However, one of them had overheated to the point that the envelope melted (!) and deformed inward in an inverted bubble. The silver at the crown of the tube was a little oxidized away but there was no hint of singeing on the plates. Obviously zapped. I know: should have replaced the tubes long ago but I'm used to colder biased Traynors that use up a pair of EL-34s about once a century.
So. Do I:
a) Replace the tubes and try it out to check for function? If so, is there a close replacement for the old Svets that doesn't require a bias reset?
b) Or do I simply convey it forthwith and henceforth to the local amp tech without passing GO or collecting $200?
Got any idea of the cost if there is collateral damage? I figure about $85 bench fee for biasing if I remember right, plus tubes. Obviously there would be troubleshooting as well if we've zapped anything else. Can you help me keep from wasting money?
Thanks boonches!
Bob
Power light still on but I shut her down immediately and let her cool. The fuse is good. The trannies look pristine, no color or leakage. No smell and I didn't let the smoke out. I opened up the tube cage and checked the original 1996 Huntsville/Petrograd Svetlana EL34s that are set horizontally at the bottom of this chassis. No carbon trace on the pins. However, one of them had overheated to the point that the envelope melted (!) and deformed inward in an inverted bubble. The silver at the crown of the tube was a little oxidized away but there was no hint of singeing on the plates. Obviously zapped. I know: should have replaced the tubes long ago but I'm used to colder biased Traynors that use up a pair of EL-34s about once a century.
So. Do I:
a) Replace the tubes and try it out to check for function? If so, is there a close replacement for the old Svets that doesn't require a bias reset?
b) Or do I simply convey it forthwith and henceforth to the local amp tech without passing GO or collecting $200?
Got any idea of the cost if there is collateral damage? I figure about $85 bench fee for biasing if I remember right, plus tubes. Obviously there would be troubleshooting as well if we've zapped anything else. Can you help me keep from wasting money?
Thanks boonches!
Bob
