I've been running with my Tubelab Simple SE, for a year now without any problems whatsoever, but suddenly while I was in another room (while it was on and played music), it had blown the fuse. So I took it apart and just looked for something that could have caused it to blow the fuse, I put in a new fuse, which it blew instantly again.
So I took out the PT and OPT's (Edcor XPWR059 and CXSE25-4-5K) from it, because I had this idea to assemble a KT88 SE, from Mikael abdellah's schematics.
So now I've assembled it, but it too blows the fuse instantly, even though I been looking for short circuit several times (and when I say it blows the fuse, it shatters the fuse).
But could it have something to do with the transformers?
And if it has, would it be possible to take the PT out again, and just hook it up to the main, and check the voltage readings, or does it have to have a load on it?
---
David
So I took out the PT and OPT's (Edcor XPWR059 and CXSE25-4-5K) from it, because I had this idea to assemble a KT88 SE, from Mikael abdellah's schematics.
So now I've assembled it, but it too blows the fuse instantly, even though I been looking for short circuit several times (and when I say it blows the fuse, it shatters the fuse).
But could it have something to do with the transformers?
And if it has, would it be possible to take the PT out again, and just hook it up to the main, and check the voltage readings, or does it have to have a load on it?
---
David
I'm not sure, are you using the same tubes or same transformer as before?
Do you mean the glass breaks on the fuse?
What are you using for a rectifier? (Not familiar with the SE)
You should have checked the transformers for shorts when you assembled the new one.
You can check for transformer problems without power.
I don't see a problem with, perhaps I am wrong, about removing the OPT to check the PT, remove the tubes first.
If all is well and you still pop fuses, try some different tubes.
Good luck.
Do you mean the glass breaks on the fuse?
What are you using for a rectifier? (Not familiar with the SE)
You should have checked the transformers for shorts when you assembled the new one.
You can check for transformer problems without power.
I don't see a problem with, perhaps I am wrong, about removing the OPT to check the PT, remove the tubes first.
If all is well and you still pop fuses, try some different tubes.
Good luck.
You don't say what fuse it blows?
On B+ or mains supply?
If its the mains fuse..you can put the OP leads into block connectors to isolate them and put a mains fuse in connect to the mains then check V out if all is OK check the diodes on the rectifier with power OFF...Remember some meters won't read on the Ohms range so you need diode check to overcome the .5V drop..
If the mains fuse blows with no outputs connected.....they must be isolated from each other...not shorted togeather..LOL
Then the power Tx is stuffed....Remember to put an earth on the Tx..Just in case its a short to Gnd on the Tx and don't hold it while testing..LOL
Regards
M. Gregg
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I think you committed the cardinal sin of debugging. Modifying the circuit to an entirely different circuit in an attempt to fix the problem with the original circuit. Always fix the circuit, then modify it. Just my two cents worth...
It takes a significant amount of energy to shatter a fuse. I'm assuming you have the fuse in series with the power transformer primary.
Disconnect the power transformer from the circuit and mains. Measure each winding (both on the primary and secondary) with an ohmmeter. Expect to see resistances on the order of 10's of ohms maybe upward of 100 ohm. If any of the high voltage windings measure close to 0 ohm, the power transformer is shot. A high current filament winding will probably measure a few ohms. That's OK.
Now isolate all secondary wires using a terminal block. Leave them all disconnected. Connect the primary to AC mains through a fuse. Turn the power on. If the fuse does not blow, the power transformer is OK - you can verify the secondary voltages to be sure (be careful HIGH VOLTAGE!!).
If the transformer passes so far, the fault that causes the fuse to explode must be in the amp. I'm betting on the supply.
Make sure all supply caps are fully discharged. Pull all tubes. Using an ohmmeter, measure across the main reservoir cap. If you measure close to 0 ohm, the cap has failed. You should see a relatively high resistance that appears to be rising if you leave the ohmmeter connected for a while.
Measure the diodes - preferably with a DMM that has a diode setting. In one direction, you should see a 0.7 V drop. In the other, the meter should read infinite (no conduction).
Repeat for remaining supplies (bias, filament, etc).
If all this checks out, connect the power transformer to the supply but leave out the tubes in the amp section. Turn power on, measure B+.
I suspect either the rectifier diodes or the reservoir cap have failed.
~Tom
It takes a significant amount of energy to shatter a fuse. I'm assuming you have the fuse in series with the power transformer primary.
Disconnect the power transformer from the circuit and mains. Measure each winding (both on the primary and secondary) with an ohmmeter. Expect to see resistances on the order of 10's of ohms maybe upward of 100 ohm. If any of the high voltage windings measure close to 0 ohm, the power transformer is shot. A high current filament winding will probably measure a few ohms. That's OK.
Now isolate all secondary wires using a terminal block. Leave them all disconnected. Connect the primary to AC mains through a fuse. Turn the power on. If the fuse does not blow, the power transformer is OK - you can verify the secondary voltages to be sure (be careful HIGH VOLTAGE!!).
If the transformer passes so far, the fault that causes the fuse to explode must be in the amp. I'm betting on the supply.
Make sure all supply caps are fully discharged. Pull all tubes. Using an ohmmeter, measure across the main reservoir cap. If you measure close to 0 ohm, the cap has failed. You should see a relatively high resistance that appears to be rising if you leave the ohmmeter connected for a while.
Measure the diodes - preferably with a DMM that has a diode setting. In one direction, you should see a 0.7 V drop. In the other, the meter should read infinite (no conduction).
Repeat for remaining supplies (bias, filament, etc).
If all this checks out, connect the power transformer to the supply but leave out the tubes in the amp section. Turn power on, measure B+.
I suspect either the rectifier diodes or the reservoir cap have failed.
~Tom
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@Alvis:
I haven't even got to put in tubes in yet, but I have planned to use the same tubes (except in the start, where I plan to use some cheaper tubes...) and it is the same transformers as before.
And yes the glass break, and there is practically smoke everywhere...
Both in the old and in the new I'm using a tube rectifier (5U4-GB in the new and 5AR4 in the old)
@tomchr
I'm not modifying the circuit, I've started from scratch and have just taken the transformers and the tubes from the old amp, and started building an entirely new amp.
And yes I have the fuse in series with the power transformer primary.
But I will try disconnect the PT from the circuit, and measure the windings...
I have taken the power supply from this design:
---
David
I haven't even got to put in tubes in yet, but I have planned to use the same tubes (except in the start, where I plan to use some cheaper tubes...) and it is the same transformers as before.
And yes the glass break, and there is practically smoke everywhere...
Both in the old and in the new I'm using a tube rectifier (5U4-GB in the new and 5AR4 in the old)
@tomchr
I'm not modifying the circuit, I've started from scratch and have just taken the transformers and the tubes from the old amp, and started building an entirely new amp.
And yes I have the fuse in series with the power transformer primary.
But I will try disconnect the PT from the circuit, and measure the windings...
I have taken the power supply from this design:
HTML:
http://diyaudioprojects.com/Tubes/KT88/---
David
First you need a light bub tester:
http://www.diyaudio.com/forums/power-supplies/167579-light-bulb-tester.html
http://www.diyaudio.com/forums/power-supplies/167579-light-bulb-tester.html
You didn't test the transformer first? Tsk tsk.
Judging by your description,it instantly blew the fuses in both amps? I'm gonna take a wild guess and say that your transformer may be bad. (shorted turns,or something.)
Take it out and test it with a DMM,come back and post the winding resistances.
Judging by your description,it instantly blew the fuses in both amps? I'm gonna take a wild guess and say that your transformer may be bad. (shorted turns,or something.)
Take it out and test it with a DMM,come back and post the winding resistances.
I don't know this amplifier but regarding diodes (if it has diode rectification) I had one a few weeks ago that I repaired: it has a hybrid bridge - two damper diodes and two silicon diodes. Took it to the chap's house plugged it in and am embarrassed to say that the fuse did not blow but there was a loud buzzing from the power transformer. I switched off very quickly and found the transformer to be very hot. A 1000V diode had let go and was short-circuit.
Worth a look
Paul
Worth a look
Paul
when fuses shatter, its usally becuase the voltage rating of the fuse is too low for the circut in question...common on the B+ side of he circut. The issue is if the rating is too low....the current rides the melted fuse element a little longer and continues to maintain the circut. Whereas a higher voltage rated fuse will break the circut as soon as the fuse element is compromised.
I've now taken the PT totally out of the circuit, and isolated all the secondary wires, and just connected it to the main with a fuse, and the fuse blows immediately (not shatter, just blow...), so I figure it's the PT which have given up?
And when I try measure each windings, it gives me:
Secondary:
Red-red (375-375) = 4.1 ohms
Red-bla/red (375-HV C.T) = 30.1 ohms
Yellow-yellow (3.15-3.15) = 1.0 ohm
Brown-brown (2.5-2.5) = 1.0 ohm
Primary:
Green/white-black (120-120) = 5.5 ohms.
But won't you think it's just the PT which is shot?
---
David
And when I try measure each windings, it gives me:
Secondary:
Red-red (375-375) = 4.1 ohms
Red-bla/red (375-HV C.T) = 30.1 ohms
Yellow-yellow (3.15-3.15) = 1.0 ohm
Brown-brown (2.5-2.5) = 1.0 ohm
Primary:
Green/white-black (120-120) = 5.5 ohms.
But won't you think it's just the PT which is shot?
---
David
David,
Check and compare primary resistance of your OP Transformers just make sure they are OK..
You seem to have some strange readings On the power Tx..I think the question has to be is it just a power Tx failure or is it a circuit failure that has taken out the power Tx..
This is important..you don't want to use another power Tx and damage it..from a faulty circuit..
If you can check the rectifier on the circuit and also with tubes out the heater connections. If you are using the same components in this build as the last then you may have transfered the fault..Are these the same components transfered from the faulty amp?
Recheck your readings on the power Tx..are you sure you have the correct colours for the windings<<as above the 30 Ohm CT is strange..4.1 end to end..?
What size mains fuse are you using?
Regards
M. Gregg
Check and compare primary resistance of your OP Transformers just make sure they are OK..
You seem to have some strange readings On the power Tx..I think the question has to be is it just a power Tx failure or is it a circuit failure that has taken out the power Tx..
This is important..you don't want to use another power Tx and damage it..from a faulty circuit..
If you can check the rectifier on the circuit and also with tubes out the heater connections. If you are using the same components in this build as the last then you may have transfered the fault..Are these the same components transfered from the faulty amp?
Recheck your readings on the power Tx..are you sure you have the correct colours for the windings<<as above the 30 Ohm CT is strange..4.1 end to end..?
What size mains fuse are you using?
Regards
M. Gregg
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I've now measured all the windings on both the PT and OPT's again, and the readings are:
Primary PT:
120-120 (green/white -> black) = 6.5 ohms
Secondary PT:
3.15-3.15 (yellow -> yellow) = 1.1 ohms
CT-3.15 (white/yellow -> yellow) = 1.5 ohms
375-375 (red -> red) = 4.2 ohms
CT HV-375 (black/red -> red) = 27.5-30.3 ohms
2.5-2.5 (brown -> brown) = 1.1 ohms
CT-2.5 (white/brown -> brown) =) 1.2 ohms
Primary OPT:
Plate - screen (blue -> white/blue) = 53.0-53.4 ohms
B+ - plate (red -> blue) = 85 ohms
B+ - screen (red -> white/blue) = 33-35 ohms
Secondary OPT: 1.4 ohms
But the only parts I've taken from the old amp, is the PT and OPT's, all the other parts are brand new (and some of them is bought at the same time).
And the mains fuse I'm using is 1A slow blow...
---
David
Primary PT:
120-120 (green/white -> black) = 6.5 ohms
Secondary PT:
3.15-3.15 (yellow -> yellow) = 1.1 ohms
CT-3.15 (white/yellow -> yellow) = 1.5 ohms
375-375 (red -> red) = 4.2 ohms
CT HV-375 (black/red -> red) = 27.5-30.3 ohms
2.5-2.5 (brown -> brown) = 1.1 ohms
CT-2.5 (white/brown -> brown) =) 1.2 ohms
Primary OPT:
Plate - screen (blue -> white/blue) = 53.0-53.4 ohms
B+ - plate (red -> blue) = 85 ohms
B+ - screen (red -> white/blue) = 33-35 ohms
Secondary OPT: 1.4 ohms
But the only parts I've taken from the old amp, is the PT and OPT's, all the other parts are brand new (and some of them is bought at the same time).
And the mains fuse I'm using is 1A slow blow...
---
David
Power Tx is short...as above.
My guess is there may have been a fault on the other amp possibly rectifier..If you replace the power Tx make sure that each winding can carry the load..
Still test your rectifier and that the heater wiring is not short with the tubes out..before you power up. Would still be a good idea to check polarity of parts and check the circuit for any possible mistakes..
Regards
M. Gregg
My guess is there may have been a fault on the other amp possibly rectifier..If you replace the power Tx make sure that each winding can carry the load..
Still test your rectifier and that the heater wiring is not short with the tubes out..before you power up. Would still be a good idea to check polarity of parts and check the circuit for any possible mistakes..
Regards
M. Gregg
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