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#1
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Jolida Blowing Tubes
A loud pop! A bright orange tube, and a completely blown fuse.
That's what I get, and right in the middle of "Glass Onion" from the "White Album" damnit! I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it for about 2 and one half years now. It blows tubes every six months. I know this can't be right. After the last set of tubes went I called Jolida, and asked them what they thought the problem might be. They explained that my Svetlanas are not quite as reliable so I should switch to Sovtek. My father's Conrad Johnson is going about 3 years strong on the same set of Svetlanas, but I took the bait anyway. The switch to Sovtek solved nothing. I follow the manufacturer's guidelines, I check the bias frequently, and it couldn't have better ventilation. Any other Jolida users suffering the same problems? What causes tubes to blow like this taking the fuse with them and all? I even think I may have seen smoke! Is this typical when a tube dies, or does it indicate a problem with the amp? The tubes in my guitar amp always seem to die a quiet death, but the Jolida likes to make them go out with a bang. Thanks, Robert |
#2
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Is the loud "pop" from a speaker? If so then it is likely the
result of the fuse blowing. We are not generally good at questions about branded amps because must of us round here make our own. In fact I don't think we really understand why some people have amps with names. Some kind of circuit description is therefore necessary for a sensible reply. You have a problem of catastrophic bias failure that cannot be the fault of the valves. I suspect you may be suffering a short somewhere when the amp gets hot. If it is fixed bias, a trapped wire can eventually short against the chassis when the insulation creeps. That might have no effect other than to stop the bias to one or more valves, resulting in the symptoms you describe. Such an intermittent, temperature-sensitive fault can be very hard to track down. Or anything else in the power stage grid or cathode circuits that might fail when hot...coupling capacitors, cathode resistor bypass caps if it is autobias. Most other faults would not be temporarily overcome by changing valves. If you let the amp cool down, change the fuse, and power up without changing the valves, does it work OK again for a while? I don't recommend switching it on for more than a few moments until you have established the cause of failure. Jolida are being naughty if they say catasrophic failure is down to the brand of valve. There may be a problem with some valves dying slowly, but the bright orange scenario is an amp problem for sure. cheers, Ian "Robert Philbeck" wrote in message om... A loud pop! A bright orange tube, and a completely blown fuse. That's what I get, and right in the middle of "Glass Onion" from the "White Album" damnit! I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it for about 2 and one half years now. It blows tubes every six months. I know this can't be right. After the last set of tubes went I called Jolida, and asked them what they thought the problem might be. They explained that my Svetlanas are not quite as reliable so I should switch to Sovtek. My father's Conrad Johnson is going about 3 years strong on the same set of Svetlanas, but I took the bait anyway. The switch to Sovtek solved nothing. I follow the manufacturer's guidelines, I check the bias frequently, and it couldn't have better ventilation. Any other Jolida users suffering the same problems? What causes tubes to blow like this taking the fuse with them and all? I even think I may have seen smoke! Is this typical when a tube dies, or does it indicate a problem with the amp? The tubes in my guitar amp always seem to die a quiet death, but the Jolida likes to make them go out with a bang. Thanks, Robert |
#3
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Hi RATs!
Take your amp to a tech and get it fixed. You are too far from the problem to solve it yourself. It ain't the tubes Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
#4
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"Ian Iveson" wrote in message ...
Is the loud "pop" from a speaker? If so then it is likely the result of the fuse blowing. We are not generally good at questions about branded amps because must of us round here make our own. In fact I don't think we really understand why some people have amps with names. Some kind of circuit description is therefore necessary for a sensible reply. I'm not sure what a circuit description should encompass, but here is a link to the specs. http://www.jolida.com/catalogue/jd302b.html You have a problem of catastrophic bias failure that cannot be the fault of the valves. I suspect you may be suffering a short somewhere when the amp gets hot. If it is fixed bias, a trapped wire can eventually short against the chassis when the insulation creeps. That might have no effect other than to stop the bias to one or more valves, resulting in the symptoms you describe. Such an intermittent, temperature-sensitive fault can be very hard to track down. It is adjustable bias. Or anything else in the power stage grid or cathode circuits that might fail when hot...coupling capacitors, cathode resistor bypass caps if it is autobias. Most other faults would not be temporarily overcome by changing valves. If you let the amp cool down, change the fuse, and power up without changing the valves, does it work OK again for a while? I don't recommend switching it on for more than a few moments until you have established the cause of failure. I installed another fuse and it blew the second I turned the amp on. The culprit tube also lit up white. I changed the tube, put in a new fuse, rebiased the amp and all seems fine. But I know It's running on borrowed time based on past experiance. Jolida are being naughty if they say catasrophic failure is down to the brand of valve. There may be a problem with some valves dying slowly, but the bright orange scenario is an amp problem for sure. cheers, Ian Thanks so much for your help. If the information I've given here provides you with anymore insight to the problem please let me know. I plan to take it to a tech, but just like to arm myself with as much undertsnadin as possible regarding things like this. Thanks again. Robert "Robert Philbeck" wrote in message om... A loud pop! A bright orange tube, and a completely blown fuse. That's what I get, and right in the middle of "Glass Onion" from the "White Album" damnit! I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it for about 2 and one half years now. It blows tubes every six months. I know this can't be right. After the last set of tubes went I called Jolida, and asked them what they thought the problem might be. They explained that my Svetlanas are not quite as reliable so I should switch to Sovtek. My father's Conrad Johnson is going about 3 years strong on the same set of Svetlanas, but I took the bait anyway. The switch to Sovtek solved nothing. I follow the manufacturer's guidelines, I check the bias frequently, and it couldn't have better ventilation. Any other Jolida users suffering the same problems? What causes tubes to blow like this taking the fuse with them and all? I even think I may have seen smoke! Is this typical when a tube dies, or does it indicate a problem with the amp? The tubes in my guitar amp always seem to die a quiet death, but the Jolida likes to make them go out with a bang. Thanks, Robert |
#6
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Thanks Xavier. Forgot about DrTube. Nice simple design.
cheers, Ian "Xavier van Unen" wrote in message ... Hi Robert and Ian, Some kind of circuit description is therefore necessary for a sensible reply. See: www.DrTube.com/audioamp.htm#Jolida for a circuit of the 302 and 502. Regards Xavier. |
#7
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Almost certainly coupling caps, Robert.
Fixed bias is the same thing as adjustable bias, paradoxically :-) It means that you have to fix it...it is not automatic. If you look at the circuit diagram, the output section is the top right-hand quarter. All current passing through the power valves passes also through the 1ohm resistors, R17 and R18, at the cathodes. The test points are shown, and you should be able to see that for each 1 mA passing through a valve, you get 1mV at the corresponding test point. The anode and screen of each valve is connected to the HT, or B+ supply, in your case around 500V. The cathodes are grounded via R17 and R18. All this part of your amp is OK. Turning to the grids, the important points are the junctions of C3/R9/R13, and C4/R12/R16. At each of these two points, the bias voltage (via R9/R12) is combined with the signal voltage (via C3/C4) and applied to the grids (via R13/R16). The negative DC bias voltage at those points is adjusted with pots RV2/RV3. As you vary the voltage, you change the current passing through the valves, and hence the voltage at the test points. The bias circuit is made to be reliable, fail-safe, and temperature-stable. The pots can go open or short-circuit in any combination and some bias will remain. If R9 or R12 fail to open-circuit, or if they are shorted to ground, then you will lose bias. This is unlikely IMO unless you have a wire touching the chassis where it shouldn't. And an EL34 should be able to cope with zero bias for a while. Decent ones can get hot enough to melt the glass (and often do in Marshalls) and still be OK (ish). So failed bias would probably not explain why your valves fail. Oh...except I notice there are no screen resistors, so I suppose you might be burning the screens. On the other side of the coupling caps, C3/C4, you have over 400V (C6 seems under-specified for voltage btw). If one fails to a short or a low resistance then the grids will go positive and current will flow through the delicate grid wires. Enough current can damage the grid and if it burns who knows where it might dangle and what fireworks might ensue. Without the grid you have a diode :-( You are lucky that the output transformer seems to have survived all that current. This doesn't explain the regularity of your 6 monthly failures. Perhaps it gets hot twice a year where you are? The technician might ask what kind of replacement coupling caps you want. Perhaps that will be your next question. Oh, and rats is us. Should be ravs, I think. cheers, Ian "Robert Philbeck" wrote in message om... "Ian Iveson" wrote in message ... Is the loud "pop" from a speaker? If so then it is likely the result of the fuse blowing. We are not generally good at questions about branded amps because must of us round here make our own. In fact I don't think we really understand why some people have amps with names. Some kind of circuit description is therefore necessary for a sensible reply. I'm not sure what a circuit description should encompass, but here is a link to the specs. http://www.jolida.com/catalogue/jd302b.html You have a problem of catastrophic bias failure that cannot be the fault of the valves. I suspect you may be suffering a short somewhere when the amp gets hot. If it is fixed bias, a trapped wire can eventually short against the chassis when the insulation creeps. That might have no effect other than to stop the bias to one or more valves, resulting in the symptoms you describe. Such an intermittent, temperature-sensitive fault can be very hard to track down. It is adjustable bias. Or anything else in the power stage grid or cathode circuits that might fail when hot...coupling capacitors, cathode resistor bypass caps if it is autobias. Most other faults would not be temporarily overcome by changing valves. If you let the amp cool down, change the fuse, and power up without changing the valves, does it work OK again for a while? I don't recommend switching it on for more than a few moments until you have established the cause of failure. I installed another fuse and it blew the second I turned the amp on. The culprit tube also lit up white. I changed the tube, put in a new fuse, rebiased the amp and all seems fine. But I know It's running on borrowed time based on past experiance. Jolida are being naughty if they say catasrophic failure is down to the brand of valve. There may be a problem with some valves dying slowly, but the bright orange scenario is an amp problem for sure. cheers, Ian Thanks so much for your help. If the information I've given here provides you with anymore insight to the problem please let me know. I plan to take it to a tech, but just like to arm myself with as much undertsnadin as possible regarding things like this. Thanks again. Robert "Robert Philbeck" wrote in message om... A loud pop! A bright orange tube, and a completely blown fuse. That's what I get, and right in the middle of "Glass Onion" from the "White Album" damnit! I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it for about 2 and one half years now. It blows tubes every six months. I know this can't be right. After the last set of tubes went I called Jolida, and asked them what they thought the problem might be. They explained that my Svetlanas are not quite as reliable so I should switch to Sovtek. My father's Conrad Johnson is going about 3 years strong on the same set of Svetlanas, but I took the bait anywa y. The switch to Sovtek solved nothing. I follow the manufacturer's guidelines, I check the bias frequently, and it couldn't have better ventilation. Any other Jolida users suffering the same problems? What causes tubes to blow like this taking the fuse with them and all? I even think I may have seen smoke! Is this typical when a tube dies, or does it indicate a problem with the amp? The tubes in my guitar amp always seem to die a quiet death, but the Jolida likes to make them go out with a bang. Thanks, Robert |
#8
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Hi RATs!
Rec.Audio.Tubes DrTube good! Is it always the same tube? If R9 or R10 is open, then if the VR, or RV, pot goes open, there is no bias. Not good. Good design, but, not everything in reality does what it was intended to do. Well, except me Happy Ears! Al Alan J. Marcy Phoenix, AZ PWC/mystic/Earhead |
#9
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Sounds like plate to grid cap is shorting. Bias supply may be bad but I dont
think it could cause this much damage so I lean more toward B+ from the driver getting to the grids. There may be a problem in the screen circuit. I dont know how they derive the screen voltage but if it suddenly shoots up to the B+ value it could fry the tubes also. When I build an amp I put a big zener diode from the screen to ground and a fuse in the screeen circuit. If the voltage goes above the zener's cut on point the fuse blows. Tubes are just to damn expensive not to protect them. "Robert Philbeck" wrote in message om... A loud pop! A bright orange tube, and a completely blown fuse. That's what I get, and right in the middle of "Glass Onion" from the "White Album" damnit! I've got a Jolida Sj 302A that uses type El-34 Tubes. I've had it for about 2 and one half years now. It blows tubes every six months. I know this can't be right. After the last set of tubes went I called Jolida, and asked them what they thought the problem might be. They explained that my Svetlanas are not quite as reliable so I should switch to Sovtek. My father's Conrad Johnson is going about 3 years strong on the same set of Svetlanas, but I took the bait anyway. The switch to Sovtek solved nothing. I follow the manufacturer's guidelines, I check the bias frequently, and it couldn't have better ventilation. Any other Jolida users suffering the same problems? What causes tubes to blow like this taking the fuse with them and all? I even think I may have seen smoke! Is this typical when a tube dies, or does it indicate a problem with the amp? The tubes in my guitar amp always seem to die a quiet death, but the Jolida likes to make them go out with a bang. Thanks, Robert |
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