Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on June 04, 2012, 08:10:13 pm
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OK I have seen something new today:
Why would Power transformer bolts get hot - and within a few minutes as well - 2 seem normal, one seems warm but one is REAL HOT!
what on earth would cause that?
The transformer is brand new as are the tubes and main board comprising of rectifier and filter caps.
I have two theories -
1)the PT is quite a buzzer' its a bit noisy apparently the vibration can create heat? I have tightened the nuts as tight as I deem safe to do so I would not like to tighten further.
2)the bolt itself is creating a loop for a short to carry voltage (hence my chassis voltage measuring thread earlier.)
anyone come across this before?
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What do you have grounded there at the PT bolts? Maybe you should check for voltage differential. The PT might be buzzing in a struggle to maintain current. Also my Fender chassis get plenty hot with upside down tubes during a gig and the part that is closer to the power tubes gets the hottest. Send a pic--it could help. Jim
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> transformer is brand new
Call the company. This is very odd, and possibly a mistake.
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Its possible that its the new transformer but i'd like to rule all else out.
Is it safe enough to bypass the IEC board i could rig a fused mains cabe straight to the primary tabs of the PT?
I figure if i did this and the bolts still heated up the PT would be a good bet?
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Those Marshall amps are famous for poor grounds and loose push-on connectors.There is a lot of current running through a poor connection that can cause heat.
Check,clean and tighten all connections to ground and heater push-on connectors especially.The most current is in the heaters.
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Thanks , will do -
Only thing is it heats up the bolts well 2 of them with all secondaries disconnected.
I daren't tighten them any more - i have read somewhere that the tiny vibrations of the PT can cause heat though am unsure of the truth in it.
the weird thing is if i cup the transformer with my hands it is not warm its only the 2 bolts that are heating up and then radiating heat into the endbell.
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Only thing is it heats up the bolts well 2 of them with all secondaries disconnected.
have read somewhere that the tiny vibrations of the PT can cause heat though am unsure of the truth in it.
No current draw on the secondaries and it's getting hot? That sounds like an internal short too me or just a really badly designed PT or realy cheap materials?
No way would I cup both hands around this PT with it hooked up to wall voltage.
Why only 2 mounting bolts that are getting hot? Is this showing an area where there's a design flaw or bad/flawed materials/bad/loose wind or a very slight short or leakage of some kind? I don't know if the last one is even posible.
Brad :think1:
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Do the transformer bolts have those insulating washer on the bell ends?
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the weird thing is if i cup the transformer with my hands it is not warm its only the 2 bolts that are heating up and then radiating heat into the endbell.
Shorted laminations. The bolts make contact with the lams in at least two places and conduct magnetically.
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hehe dont worry I'm not that bad it was a figure of speech - i wouldn't grab hold of anything with both hands.
yes the bolt goes like this:
bolt head : metal washer : fiber washer : endbell : PT : Chassis : fiber washer : metal washer : nut
I went and tightened them a bit more, it actually helped a tad.
The amp sounds pretty awesome - but i have never had a working JCM 2000 - i wonder do they run the PT's hot naturally.
I say this as these transformers are in my eyes small for the job - even my bandmaster has the same physical size iron for to 6l6's this thing has to power 4 x el34's
i have had it on now about an hour - checking secondary voltages and bias all are staying steady.
But the warmth of the PT worries me,
If i could get a loan of one of those current clamp metres would I be able to determine whether it was drawing excessive current? or should I say at what point should I measure?
maybe i am barking up the wrong tree.
This amp is totally depressing me
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If there's no CT on the B+ secondary, for use with a FWFB rec., it will be smaller than the same raited PT with a B+ CT.
Shorted laminations. The bolts make contact with the lams in at least two places and conduct magnetically.
I'd bet FYL's right. That I could belive.
Brad :icon_biggrin:
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FWIW, I have read the transformers are undersized and run hot. But, if it's just the bolts -very wweird indeed.
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Do the transformer bolts have those insulating washer on the bell ends?
Ding ding
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Do the transformer bolts have those insulating washer on the bell ends?
Ding ding
I should remove them?
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I wouldnt remove them unless the transformer is dead and you want to save the bell ends and all bolts etc. DING*
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Yea I think the theory is that one of your bolts is touching a portion of the lamination. Those lil collars are usually made of cheap plastic which is prone to cracking. At the very least, f the collar on either side of the end bell is intact (even excluding the inner sleeve), it should serve to center the bolt within the lamination tunnel, avoiding contact. Just a possibility. :dontknow:
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I wouldnt remove them unless the transformer is dead and you want to save the bell ends and all bolts etc. DING*
Hey plexi excuse my ignorance if I am wrong but is that awesome sarcasm right there?
I can never tell grading text unless I know the person!
Well I guess its safe enough to check it with the bolts Removed and have the pt completely floating,
If that goes well I can try refitting it with no washers.
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I wouldnt remove them unless the transformer is dead and you want to save the bell ends and all bolts etc. DING*
Hey plexi excuse my ignorance if I am wrong but is that awesome sarcasm right there?
I can never tell grading text unless I know the person!
Well I guess its safe enough to check it with the bolts Removed and have the pt completely floating,
If that goes well I can try refitting it with no washers.
No not at all. I have seen PT's with isolation washers and one's without. Also i see them at time with no inner sleeve to isolate the bolts. I tried to upload a Ding wav file but it didnt work. Im a joker at times
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Well I guess its safe enough to check it with the bolts Removed and have the pt completely floating
I don't think that's a good idea, to unbolt the laminations.
This has come up before and reasons were given why it was not a good thing to do.
Brad :icon_biggrin:
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So my only option is to try with the washers out and hope the profile of the end bell centres the bolt?
These transformers don't come with bolted laminations like many fender transformers, its the actual fitting of them into the chassis that is when the laminations are bolted.
edit -
bugger - fiber washers removed - bolts heat within one minuite... :BangHead:
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the weird thing is if i cup the transformer with my hands it is not warm its only the 2 bolts that are heating up and then radiating heat into the endbell.
Shorted laminations. The bolts make contact with the lams in at least two places and conduct magnetically.
As a conclusion
FYL must have been on the money -
A friend of mine has a similar amp - just have the PT installed and 15 minutes no hot bolts - before they were warm at 30 seconds and hottish at 2 minuites.
now for a battle with the seller of the transformer.....
Can I say a massive thank you to you all for all your input - This one has hung over me for a long time and I really was fed up with it.
I am a strong beleiver in what goes around comes around... so here's hoping you all get a bit...
thanks
:thumbsup:
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Glad you found the problem. Theres always that one amp that haunts you until you figure out the problem. I have one now in another thread