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Old 6th August 2006, 11:41 PM   #1
Jeb-D. is offline Jeb-D.  United States
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Default Transformer temperature?

I have a concern regarding my amp. It is my first power amp so I am not sure if this is normal.

The power transformers get pretty freakin hot, almost to hot to touch. Eventhough they are rated at about twice the power than what is drawn from them when at operating state. I did paint them to match the chassis, perhaps the paint is not letting them vent off heat. I've been using the amp for about a month now with no problems thus far, but am concerned that over a period of time may cause the enamel on the wires to slowly melt and short windings.

Does anyone think this is a problem, or am I being paranoid?
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Old 6th August 2006, 11:55 PM   #2
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Are they Hammonds? Hammonds do get hot. Too hot to touch is probably too hot. I go by the " if you can hold your finger on the core for several seconds without using bad language it is OK rule". I don't even remember who told me that, but it works for me.

The amp I am using now has an "Allieds own tube transformers" which are made by Hammond. The amp has been on for several hours. The power transformer is uncomfortable to touch, you really want to move your hand. I use a lot of these transformers, they all get hot and the only failure I have ever had was one that got wet during a hurricane.
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Old 7th August 2006, 12:03 AM   #3
Jeb-D. is offline Jeb-D.  United States
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They are Hammonds, good to know it's normal. I was just comparing them to the OPT's, which are luke warm; it worried me.
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Old 7th August 2006, 12:13 AM   #4
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its amazing, I was just going to ask the exact same question!

I ran my amp for 3 hours strait (party) it was almost too hot to touch. however, I kinda want to but a piece of tin foil above the tubes, and the power transformer and see if I can cook an Egg on it.

How can someone say tube amps are ineficent?!?!
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Old 7th August 2006, 12:24 AM   #5
Jeb-D. is offline Jeb-D.  United States
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Quote:
I ran my amp for 3 hours strait (party)
Were the guests impressed by the sound of the almighty tubes?
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Old 7th August 2006, 12:48 AM   #6
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First off, i would like to state that i manufacturer transformers for the guitar tube amplifers and also audio.

All transformers when they are design they are design around thic criterias
1) core size
2) core material
3) number of winding per turn
4) wire enamel class

For transformers, commercially they often optimize for watts per pound. Like hammond they trying to squeeze more watts per pound. TO do this they need to look into the number of turns and the core size and the core material.
IN short hammond will utilize the m19 grade core squeeze as much watts into a particular size.
However by doing this
1) high ambient temperature
2) high magnetic field
3) low life span
4) higher risk of chain-failure
When a trans is wound with a coil in it, what we are trying to do is to magnetize the core. The more turns we put it the more efficient the core gets magnetize. What that means is core loss will be much less this way when more turns are used. Bear in mind more turns results in lower va. When the core does not get magnetize well, this turns out to be a power loss in terms of heat and in a higher mag field. When the core can't capture the magnetizing effect, this mag field escapes into the surronding.
Core material like z11 and m6 are cores which allow easier magnetizing.

In short, higher heat result in lower efficiency, not so good sound because of high magnetic field and lower power transformer. When you scope a transformer which is overheating, you will notice a sine wave is not perfect because its reaching saturation.

Inside each transformer the wire classes are 100C,130C,155C,180C,200 and 200C
In transformers most of the time the class used is the 130C. The insulation is the polyuretherune the wire thickness is around 0.03-0.05mm. When the transformer is hot the insulation of this wires wears down faster. So in the end the thickness of insulation degrades each time you use the transformer.

SO in short get custom wound transformers for audio. The performance upgrade is so much better.
If there is more questions on transformers feel free to post will answer in time. I feel i have miss out on certain things
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Old 7th August 2006, 01:06 AM   #7
arnoldc is offline arnoldc  Philippines
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Are these Hammonds the 270 series? They really get hot. It's better if you use the 370 series.

For my PSU transformers now, I always turn to my local winder as he can make transformers a bit cooler than the Hammond and much cheaper too.
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Old 7th August 2006, 01:06 AM   #8
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Quote:
Originally posted by Jeb-D.


Were the guests impressed by the sound of the almighty tubes?
none of them were audiophilles, but they all could easily tell the difference between my homeade tube amp, and the Sony Reciver

They kept telling me how much they loved the sound, they loved the detail, and the rich tone. it got to the point where I used them to tweak things about the amp.

It was amazing, they all loved it! now they all want me to make them one....


mine is a hammond 272HX
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Old 7th August 2006, 01:39 AM   #9
Jeb-D. is offline Jeb-D.  United States
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Quote:
now they all want me to make them one....
Yeah, if they only understood how much work went into one, you'd have to charge 2K+ to even make it worth it.

Quote:
Are these Hammonds the 270 series
167 and 169 series. One for power and one for fillament. Both get hot. The OPT's are Eastern Audio's I got off ebay, that sound freakin' amazing! They get just slightly hotter than ambient temp.
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Old 7th August 2006, 02:23 AM   #10
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OPT's are limited by saturation effects which means that the core and winding size are much larger than they need to be for the power that runs through them. OPT's should never get hot due to the electrical stress. They frequently get warm from the radiant heat emitted by the surrounding tubes.

The Hammond 270 sreies all run warm to hot. The 370 series are wound to operate from 50 Hz power, which makes them run cooler on 60Hz. I have no experience running them on 50 Hz power.

It is interesting to note that the Allied power transformers are more conservatively rated than the same size Hammond. The Hammond 270FX is rated for 138 VA (60Hz only) and the identically sized Allied is rated at 113 VA (50 or 60 Hz). The Allied is cheaper, and I am cranking about 140 VA out of it on 60 Hz, yes it gets hot, no it hasn't died in 4 years of daily use. I have built about 10 of these amps in 3 years, although most are more conservatively biased.
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