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Old 25th April 2009, 08:45 PM   #1
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Default Simple SE blowing fuses

Allied 6K7VG
c-14x choke
No FREDs
No motor run cap
5AR4 rectifier (Chinese)
JJ E34L's
JJ 12AT7
Edcore GXSE15-8-5K
Triode
on test bench

So I finally powered up my Simple SE today and had the 5AR4 flash immediately. Not a big flash. Then all the tubes started to glow and the sound comes through the speakers at about 6 seconds. I start to hear a crackling and see the 5AR4 start to flash again.Then at about ten seconds the 250V, 2A fuse blows. I cant find fuses that say their slow/fast blow in this town of 7,000.

So I installed the inrush current limiter between the transformer and the power switch and tried again. No flash (immediately when switching on the power bar) on the rectifier this time but otherwise the amp still blows the fuse at about 10 seconds.

I read the Simple SE with KT88's thread and tried most of the suggestions there. My sockets are all in correctly, C1 and C2's polarity's are correct. The 10M45 ICs are good. No bad solder joints that I can see. Checked and rechecked the wiring. No resistance between T-1 red-yellow and R4. Should there be? I don't know how to check for shorts across the traces on the board. I don't know what a blown resistor looks like.

I'm going to extend the transformer wire lengths. My test bench is kind of a rats nest. I had to step away for a while.

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Old 25th April 2009, 08:58 PM   #2
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If it's blowing fuses, it's got to be a short somewhere. Diligence and an ohmmeter may be able to find it. I'd usually suspect the FREDs, but you say they were never installed.

It could be a bad tube, a stray strand of wire, a sloppy solder bridge, a bad cap, or a cap installed backwards. Other possibilities include a short in the transformers.
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Old 26th April 2009, 04:58 AM   #3
w5jag is offline w5jag  United States
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Bad rectifier tube, probably.

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Old 26th April 2009, 06:48 AM   #4
RDL_AK is offline RDL_AK  United States
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Slow blow fuses are MDL 2A

If you have another rectifier tube try it. You can try a 5U4 or 5R4 instead of the 5AR4. If you do not have another tube and
if you have the Freds install and try them without the rectifier tube. If you do not have the Freds you can use standard high current diodes that can handle the current. Don't forget to jumper switch 1 for Freds or standard high current diodes.

I can not tell if the HIGH VOLTAGE center tap is red with stripe is installed correct. All three wires look solid red in picture.

Also all the output transformer wires look white can not tell how they are wired.

Caps all look correct.

I had a problem with one Fred when I first powered up myself. I changed the freds to some old epoxy power diodes I had. But I did not know about this forum. It would have made it alot easier to resolve or prevent the problem in the first place, if I had known of this forum.
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Old 26th April 2009, 01:20 PM   #5
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Hey guys. Thanks for all your support. I couldn't have done any of this without this forum.

When I received my Allied 6K7VG one of the bells had a dent in it as if it had been dropped on the floor. I was given advice(not from this forum) that this was not a problem.

The other potential problem I caused is, I managed to melt the side of one of my Auricaps(.22uf,600v) about a 1/4" round and 1/32" deep. Should I replace it?

I have a set of FREDs that I can try out. The center tap is red with yellow stripe. I bought one 50' roll of white 22AWG wire that I'm using for everything. I will take some more pictures and post them.

I will order a new rectifier and get the Auricap at the same time if you think I should.
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Old 26th April 2009, 02:06 PM   #6
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Unless your auricaps are really melted then you shouldn't have a problem. You may want to test it to see if it's passing any dc current.

It's not blowing right away so I don't think it's your rectifier. Sounds like something is drawing a lot of power. Either a resistor value is incorrect, something is shorted, or something external to the board is miswired.

From what I can tell, your soldering looks OK. Can you share a photo of all the external bits so we can see the wiring?
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Old 26th April 2009, 02:29 PM   #7
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Quote:
When I received my Allied 6K7VG one of the bells had a dent in it as if it had been dropped on the floor. I was given advice(not from this forum) that this was not a problem.
I agree that this is not likely the problem.

Quote:
The other potential problem I caused is, I managed to melt the side of one of my Auricaps(.22uf,600v) about a 1/4" round and 1/32" deep. Should I replace it?
If the "wound" is only on the surface it won't hurt anything. I have an Auricap that got to close to the soldering iron in a Tubelab SE that works just fine. On the other hand if the cap shorted out, it could cause problems like this. Measure it with an ohm meter. If the readings are very low (under 1000 ohms) the cap is shorted and must be replaced. Otherwise lets look further.

Quote:
Bad rectifier tube, probably.
The Simple SE runs the rectifier tube near the upper edge of its surge current spec and some of the new production tubes are not so great. A bad rectifier tube is a likely possibility. There have been several reports of initial failures in new 5AR4's especially JJ tubes. One customer had two spark out instantly on power up, but the third has been running fine for over a year.

Quote:
the sound comes through the speakers at about 6 seconds
If both speakers made relatively clean sound at similar volume levels for even a brief time the amp is likely wired correctly and the caps are OK. The rectifier tube is most likely the cause. You can try the following tests if you want.

Remove all tubes, power up the amp. The fuse should not blow. Unplug the amp and wait for all caps to discharge (a few minutes).

Disconnect the choke (L1). Connect the black lead of a volt meter to GROUND. This is easily done by inserting the probe into the unused T1-red-yel screw terminal and gently tightening the screw. If your voltmeter uses clips, clip on to one of the ground side of either large white cathode resistor (the end connected to the fat ground trace on the top side of the board). Connect the red voltmeter lead to to the L1 terminal closest to the T1-red-yel terminal. Set the voltmeter to its highest DC voltage range. Insert the rectifier tube (no other tubes). Power up the amp. There should be a brief delay and the voltage should rise to over 500 volts. The fuse should not blow. If it does, the rectifier tube is likely bad. Unplug the amp and wait for the voltage to drop to a few volts.

If you got this far, re connect the choke, but disconnect both output transformers. Connect the red voltmeter lead to the T3-PRI terminal closest to the large black capacitor. Repeat the test. The voltage should again rise to over 500 volts without blowing the fuse. A blown fuse is likely a bad rectifier tube, but it could be caused by a bad electrolytic cap (I have never seen it happen).

Finally reconnect everything, and insert the 12AT7. Connect the red voltmeter lead to the lead of R4 closest to the edge of the board. Power up again. The voltage should be slightly less than before. Any fuse blowing still points to the rectifier tube since nothing draws any serious current yet.

Finally try adding one output tube and repeating the test. Use the channel with the undamaged cap. If this works, test the other tube in the same channel. If one output tube causes a blown fuse, but the other does not, that tube may be bad. If either tube causes a blown fuse, the rectifier tube is again the likely culprit since it is breaking down with load.

If all of this sounds like too much trouble, you will have to wait for a new rectifier tube. Many old rectifier tubes can spark out and still live, but this seems to be fatal in the new stuff.
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Old 26th April 2009, 03:03 PM   #8
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OK, so I look over the wiring with fresh eyes this morning and found that I had connected the 8 ohm pin to ground on one of the OPTs instead of the common.

Fixed that, installed the FREDs/SW1 jumped. Powered it up and a small puff of smoke comes off the board and the fuse blows with or without the tubes.

I checked the Auricaps and both gave the same ohms.
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Old 26th April 2009, 03:44 PM   #9
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I took the SW1 jumper off and it stayed powered without blowing a fuse and I turned it off after about 10 seconds.

I tested the rectifier the way George said and my voltmeter got to 3 V before the fuse blew. The voltage read 0 for a good 6,7 seconds after I turned it on while the rectifier started to glow.
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Old 26th April 2009, 05:13 PM   #10
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What component smoked on your board?
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