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Heathkit W4 power supply PS transformer temp
Heathkit W4 power supply PS transformer temp
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Old 20th July 2019, 07:02 PM   #1
bigbargain is offline bigbargain  United States
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Default Heathkit W4 power supply PS transformer temp

So i know they run hot and if you donít watch out youíll burn it up and wonít enjoy finding a replacement.

So as preventative maintenance decided to do more than a ďfeels hotĒ evaluation.

Here is my high tech measurement rig. Iím seeing 115 F. I am using the small paper towel scrap to reduce convection. How about others? If youíve ever measured let the rest of us know when we should get worried.

Thanks in advance!
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Old 21st July 2019, 04:52 PM   #2
scottpetersen is offline scottpetersen  United States
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If it wasn't potted, 150f is near the top for standard transformers, potted ones would be lower because of the insulating properties of the potting material.
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Old 22nd July 2019, 01:00 AM   #3
Brice is offline Brice  United States
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Run a small USB fan with flow control and the problem of heat is gone..in the summer
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Old 22nd July 2019, 01:05 AM   #4
trobbins is offline trobbins  Australia
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If possible, it could be worth reporting some other local items as a way to allow your measurement to benchmark what others could be measuring:

- mains AC voltage

- room ambient temperature

- if you have checked the output stage bias (current, voltage or tube dissipation)

You may also want to check if the measured temperature changes much if you put some more thermal insulation directly on top of the white paper toweling, to see if the thermometer bulb is being influenced by ambient air.
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Old 22nd July 2019, 01:56 AM   #5
cerrem is offline cerrem  United States
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115F is 46C which is perfectly normal ....
I have been designing transformers commercially and for Military for over 40 years... The normal standard design practice transformers of that era was 40C rise above ambient under full max continuous power conditions... This is for transformers using materials ratted for 105C which is also refered as Class A insulation...
Your good to go....
Get yourself a thermal gun...with the laser pointer...this will be a fun tool to play with...
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Old 22nd July 2019, 01:26 PM   #6
bigbargain is offline bigbargain  United States
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Thanks everyone for your responses.

Strangly, what prompted me to begin checking was when one of my pair seemed to be hotter. (I’ve since changed this) but until this weekend, i “daisy chained” the power from one amp tot he other using the accessory outlet one one of the amps to feed the other. Temperature seemed fine on both units, then i did some reorganizing and one amp seemed to be running hotter. (Pretty uncomfortable to your hand, but you can keep it on the ps tranny). And I’m a little suspicious air convection is causing the temp to be misreported. The thermal gun is a very good idea.

Since my first post I’ve added a bucking transformer and dropped the line from 118.3 to 109 and the temp dropped 5-6 degrees F.

Cerrem. Whats your opinion of my measurement rig? Would my reported temp be much higher with a gun? Do i really need to absolutely block airflow or is my small paper towel enough?

So you don’t think I'm completely crazy, these amps do have a reputation for blowing PS trannys and the world’s supply of spares, judging from ebay prices when they DO show up, are getting crazy. So I’m doing all this so our grandkids will be able to hear a heathkit w4.

Oh. And the amps are cathode biased, and i have them ac balanced, which is the only adjustment.

AND(!) I think they actually sound better running at the lower line voltage now.

Last edited by bigbargain; 22nd July 2019 at 01:28 PM.
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Old 22nd July 2019, 02:43 PM   #7
scottpetersen is offline scottpetersen  United States
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Many of those amplifiers had the coupling caps go bad, which drew too much current, which in turn burned out the transformer.
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Old 22nd July 2019, 03:59 PM   #8
jackinnj is offline jackinnj  United States
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Heathkit W4 power supply PS transformer temp
Quote:
Originally Posted by scottpetersen View Post
Many of those amplifiers had the coupling caps go bad, which drew too much current, which in turn burned out the transformer.
I had this exact issue with a Pilot amplifier's coupling caps -- leaky. Not a bad idea to check the filter cap while you're at it. My Heath Williamson doesn't run hot.
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Old 22nd July 2019, 04:19 PM   #9
bigbargain is offline bigbargain  United States
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Hmm. My amp was rebuilt q few years before i got it. He used good components he did good work and used higher quality parts. But it doesn’t hurt to check.

I don’t want to hyjack my own thread, but maybe related... I’ve ot had this on other tube amps. 2 thigs; i have a turn off thump in both mono blocks and when you cut the power, they don’t “coast” as the PS caps discharge - pretty much the sound dies immediately and there is a smqll “thump”. Thoughts?
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Old 22nd July 2019, 04:47 PM   #10
cerrem is offline cerrem  United States
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You can easily find something like Fluke 62 Laser Infrared Thermometer on eBay...... or Home Depot...
If you want to get to the bottom of this issue..... you need to check and compare current draw for both transformers..... First check the primary AC current draw from the mains...then check the secondary side DC....Most common cause is leaky filter caps in the power-supply... next would be leaky coupling caps.... If you still cant find any dependencies, I would check the AC input current , ie magnetizing current, when the secondary is completely un-loaded..
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