Just tonight my Jolida 502 has started acting up. The amp powers on and works perfectly for about 5 minutes. Then, without warning, it just shuts off. Funny thing is, it powers right back up when you press the power button. But, after 5 minutes or so, it shuts off again. I'm not running the amp hard. The volume nob never gets past 10:00. Nothing in the system has changed and the power cord is securely connected. I'm frustrated guys.
That's a good one. Obviously it's not a blown fuse because they don't self heal. Have you checked the bias on your output tubes? How many hours are on the input tubes? The funny thing is that both channels go out and not one. The power supply is common to both channels. Maybe one of the diode bridges has gone bad and when it heats up it stops conducting and shuts down the amp. Output tubes won't work with no B+ and that would knock out both channels at the same time.
I assume the amp has some type of over heating protection circuit. It'll be yet another call to Jolida today. No matter the outcome this is the end of the line for this amp and me. This will mark the 3rd time this amp has gone back for service and the 4th time overall as the original 502 was replaced by Jolida. A lemon is the term that comes to my mind. Does anybody think I'd be out of line asking them to cover my purchase price so I can just get out of this thing and move on since it's still under warranty and I'm the original owner.
Hello, Fred. Personally, I agree with mep. Definitely not out of line. One question did come to mind though, which may sway my stance. Are you using the stock tubes and if not, are you 100% sure the tubes you are using [if not stock] are rated to the plate voltage? Also, what are you biasing the tubes at compared to what the manual states.....if you don't mind me asking?
I spoke with Jolida today. The tech explained that this amp has a digital circuit that monitors output tube voltage. Whenever is senses a tube is failing it sends the unit back to standby. That's the reason why I was able to repeatedly repower the amp. Right now I have all the power tubes marked and they are all removed from the amp. The amp is turned on with only the signal tubes in place. So far 20 minutes and the amp is still on. After about 40 minutes or so if the amp hasn't turned itself off by then. I'll shut it off and then reintroduce one power tube and run the same routine. When the amp shuts off, that's the bad tube.
Probably should have bought that Hickock tube tester when I had the chance. Would have saved alot of time here.
Wow! So my question now is: What are the odds that 3 power tubes could all fail at exactly the same time? That's what seemingly has happened. The output tubes on this amp are oriented in a row. From left to right they are labeled V3, V4, V8, V7 (the signal tubes are 1,2,5,6). At time intervals ranging from 25 minutes to 6 minutes, V3, V4 & V7 all sent the amp back to standby mode. V8 has been on for over an hour and the amp is still in power mode.
Second question: If you're a Vegas odds maker, what odds do you assign to 3 of 4 power tubes failing at precisely the same time? Remember, the amp worked perfectly up until Sunday night. I mean I can't win the lottery to save my life, but I can have 3 of 4 output tubes fail at exactly the same time? C'mon Man!
By way of analogy, the overhead track light in my audio room has 6 GU-10 bulbs. If four of the six failed at the same time I would be looking for a wiring problem because there is no way that four bulbs would all just happen to expire at exactly the same time.
Has anybody else who lives with valves ever experienced this type of failure before? I would really love to know.
Hello, Fred. Personally, I agree with mep. Definitely not out of line. One question did come to mind though, which may sway my stance. Are you using the stock tubes and if not, are you 100% sure the tubes you are using [if not stock] are rated to the plate voltage? Also, what are you biasing the tubes at compared to what the manual states.....if you don't mind me asking?
Sorry to have passed over the question earlier. No, the tubes are the stock Tung Sol 6550's. They went into service in January 2011. The amp doesn't have a clock, but I would have to guess (very roughly) that they have around 800 or so hours on them. What's the average life of a 6550 anyway?
Sorry to have passed over the question earlier. No, the tubes are the stock Tung Sol 6550's. They went into service in January 2011. The amp doesn't have a clock, but I would have to guess (very roughly) that they have around 800 or so hours on them. What's the average life of a 6550 anyway?
Should be around 2000 hrs but that's a rough estimate since a lot depends on how hard the tubes are driven. 800 hrs is only slightly better than the early Sino jobs.
Should be around 2000 hrs but that's a rough estimate since a lot depends on how hard the tubes are driven. 800 hrs is only slightly better than the early Sino jobs.
After thinking it over a bit more and doing some basic math, I've had to revise the hours estimate. These tubes have been in use for around 15 months. If the amp is used 3 hours a day average then the total (assuming a 30 day calendar month) would be 1350, but if the average of 4 hours is used, then that number jumps to 1800. It's all just a guesstimate though. Some days the amp stays on for hours on end. Other days it's not turned on at all.
The other thing to consider is that the amp is connected to the Musical Fidelity 550K's. The 550's are what actually are driving the Maggies. The way I understand it is that the 550's make the amp sense a very low impedance load. I'm not an electronics guy so I don't know if that is a good or bad thing for tube life.
Well the saga appears to be over. I ordered 4 new Svetlana 6550C's and the amp is running just fine now. I guess the old TungSol's were failing after all. And as a testament to the rule that you can't test power tubes on a tester three of the four TungSol's tested "strong" on Jay's Hickok 6000, the other tested questionably, but wasn't bad. The questionable one was the only tube that wouldn't shut the amp down. Go figure. I'm glad this has worked out this way it's saved me a fortune and now I can stop looking at the Modwright website. (At least for a few weeks ) Back on track for a pair of the REL T5 subs.
Glad to hear your troubles are over. I would recommend keeping rough track of the hours on your new tubes just to see where things go. Also keep up on the bias of the tubes. Checking them periodically could save on potential premature failure.
) Back on track for a pair of the REL T5 subs.
