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Old 5th October 2008, 08:21 PM   #1
cjkpkg is offline cjkpkg  United States
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Default Rookie mistake?...Maybe...

So I have been breaking in the Simple SE amp getting all the switches in place, making sure the PT and the OPT's are all arranged correctly.

I recently rotated the PT 90deg to address a hum issue. Everything was running beautifully...until while I was in the back yard and the wife comes running out and says "I think your thing broke..." Ugh...A string whiff of melted PVC...crap...

Sift through the damage and it turns out that one of the power leads shorted out right at the exit of the PT on the PT housing.

Now, I am a rookie with tube audio but I did run all wiring through the top plate through a grommet. I swear I was gentle with the wiring. But lo and behold one of the black power leads wore through enough to short out and fry the PT...

At least the fuse blew to save the rest of the amp but the PT is definitely shot...

/Frustrated
Carl
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Old 5th October 2008, 09:13 PM   #2
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Crap, Crap & double crap....I would bet that as you rotated your power TX you took up all the slack on your leads...being as TXs' are so heavy you probably didn't notice the grommet being cut thru into the chassis.
The force applied twisting & lifting the Tx seemed to mask the action of cutting thru your lines............My best guess.
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Old 5th October 2008, 09:17 PM   #3
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To say the least (frustrating).

You might pull the end bell off and inspect more thoroughly. It's possible that the insulation was only damaged in the area of the short, in which case you could salvage things by splicing into what's left of the exposed lead inside the end bell. But if the insulation shows signs of heat damage throughout it's proximal length, you'll probably not want to attempt such a repair.

Anyway, thanks for sharing. I just inspected a still NIB 6K7Vg and the outer (clear) layer of the insulation on three leads shows signs of stress from contact with the opening in the end bell. I've taken the precaution of placing a length of heat shrink over the bundle where it contacts the end bell to prevent any further damage.
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Old 5th October 2008, 09:41 PM   #4
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by jrn77478
To say the least (frustrating).

<snip>
Anyway, thanks for sharing. I just inspected a still NIB 6K7Vg and the outer (clear) layer of the insulation on three leads shows signs of stress from contact with the opening in the end bell. I've taken the precaution of placing a length of heat shrink over the bundle where it contacts the end bell to prevent any further damage.
I've seen this in Hammonds as well (aren't the Allied transformers built under contract by Hammond?) - it seems that the endbell stampings are not deburred in the area of the lead out.. I have seen some that were quite sharp enough to damage the wires coming out, and I feel this should not be the case.

Heat shrink tubing is a good precaution and in fact some vintage Japanese power transformers I've encountered had cambric tubing on the lead outs for the same apparent reason.
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Old 5th October 2008, 09:49 PM   #5
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I agree that the transformer may not be ruined. It seems only that the wires coming out have been burnt. Take off the covers and inspect them closely like jrn77478 suggested. Repair as needed.

Victor
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Old 5th October 2008, 10:45 PM   #6
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OK fine, you've blown something up. It don't mean you can call yourself an engineer. When you've blown up dozens of things like I have, then perhaps...

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Old 6th October 2008, 02:12 AM   #7
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I agree that it may be possible to fix the transformer if one of the black leads shorted out.

Think about what would happen if a black lead shorted to the chassis. There are two possibilities. If the black wire that was connected to the neutral side of the power line shorted to the chassis, nothing bad should have happened except maybe some hum. If the black wire that was connected to the hot side of the power line shorted to the chassis there should have been a big bang and a blown fuse without much other damage, provided you had the chassis properly grounded. If it wasn't grounded then the AC line current went somewhere, somewhere bad. Be glad it wasn't someone.

Assuming that the line current flowed from the black wire through the chassis to ground probably burning the insulation and maybe the conductor. Carefully open the transformer up. If the black wire was fried, but the windings look OK it may be possible to repair the black wire and insulate it with heat shrink tubing. If you do this, after reassenbly measure the resistance from the windings to the core and make sure there is no continuity. Then make sure that the chassis is grounded before using it.
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Old 6th October 2008, 12:09 PM   #8
cjkpkg is offline cjkpkg  United States
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Thanks for the replies guys. I will take the covers off and inspect. Unfortunately I suspect that it was indeed the hot that shorted out. All of the burning seemed to have taken place inside the PT. The board and rest of the components look OK.
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Old 6th October 2008, 12:27 PM   #9
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Note to self... replace slo-blo fuse in my Simple SE with a 1.5 amp fast blow.

Sorry to hear about your mishap. Hopefully you'll be able to repair the PT. It's a shame to have to lose a $50 transformer. Why is it that the ten cent resistors never die?
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Old 10th October 2008, 10:01 PM   #10
cjkpkg is offline cjkpkg  United States
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Man,

I give Allied an A+ for cust service. I had emailed allied about my situation. Documented exactly what happened and voiced concerns around "things I have heard" about other people agreeing that the opening in the end bell has some sharp edges.

They got back to me after a day and said that they will issue an RA# and to send the old one back. I got a phone call asking if I needed to speak to a tech about anything, I said no the 6K7VG is exactly what I want. Another day goes by and they say to just pitch the old one and they are sending me a new one.

Good deal...now I will really have to dismantle the old one fully to see if it can be reborn...
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