Troubleshooting hot transformer in TSE, where to start? - diyAudio
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Old 2nd January 2014, 06:42 PM   #1
pbkrag is offline pbkrag  United States
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Default Troubleshooting hot transformer in TSE, where to start?

I have the edcor XPWR131 trafo running, 300bs with 5ar4/gz34 b+ is 370v at 60 MA. The 5842s are at 175v, I belive this is about 10ma. The trafo gets hot. I can hold a finger on it for maybe 2 seconds.

I think I'm not overloading the transformer. rated for 175ma and I think I'm drawing 140.

When I breadboarded it, I thought it was a bit hot compared to my SSE (xprw035, barely gets warm) , but I think it may have gotten worse when I mounted it in the chassis. Not sure if the lack of airflow for the components in the chassis is responsible (the transformer is open to the air, not inside the chassis so it gets fine ventilation) or if I changed or broke something when I re-assembled it. It did have an issue with the Voltage regulator shutting down, but I resolved that. I beefed up the heatsink, and also noticed it was little loose when I put the new heatsink on, tightened it up, and added some ventalation holes on top. So, no more shutdown but the trafo still gets very hot.
I've tried a few other rectifier tubes 5v4 and 5u4gb. They get lower b+ and also the transformer runs hot.

Another wierd thing, I don't know if its a clue or related. At startup plate voltage on one of the 5842s shoots up to about 500v, then after a min or so comes down to 175v. No sound comes from that channel til it gets around 200v
Overall everything sounds fine.
So is this hotness normal? Is it clearly a defect in the transformer? or Something I did? any suggestions on where to start troubleshooting would be appreciated.
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Old 5th January 2014, 02:16 AM   #2
rknize is offline rknize  United States
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My 131 gets fairly toasty when running the 300Bs. I haven't had any problems with it, though. You have to look at the entire transformer VA. You are fine on the HT winding as you say, but the heaters on 300Bs draw a lot of current...some more than others. For example, WE specs something like 1.2A per filament. Some 300Bs out there draw more like 1.5A or more. The 6.3V winding is rated for 4A (it also powers the 5842 heaters). I probably should have spec'ed 5A to give the design more margin. I also wish I had dropped the HT taps to 250-0-250 for 45 use. Oh well.
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Old 5th January 2014, 02:55 AM   #3
pbkrag is offline pbkrag  United States
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Thanks for the reply Russ,

How hot do you think yours gets?
I'm not so sure your specs are underrated. Even at 1.5 for the 300Bs. According to the raytheon data sheet the 5842s are .3ma /tube. Maybe a misprint/misread? but 1.5 x 2 plus the .6ma, 3.06 amps? seems within spec.

I put a thermometer (one I use for cooking) on the top of the transformer and it reads 130 deg F. is that hot? too hot? Not sure if that's an accurate measurement. I can't touch it for more than 2 seconds I would think that was hotter
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Old 6th January 2014, 07:50 PM   #4
rknize is offline rknize  United States
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The 5842s are 300mA each (0.3A). So we are pushing 3.6A through a 4A winding. The 5V winding has an extra amp of capacity to be able to handle a 5U4. Technically it should not be overloading the tranny, but it is obviously being pushed pretty hard.

It's been a long time since I powered up my TSE, which still lives on a breadboard. My queue of projects at home is growing faster than I can manage them, so it has been that way for years now. I do remember that after a few hours, the transformer got quite hot. If I measured it, I don't remember what temperature I saw. It was hot enough to make be rethink my chassis design a bit.
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Old 7th January 2014, 04:08 PM   #5
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I too have an Edcor XPWR131 running, 300B's with an 5AR4. I am at about 387v B+ and 65Ma. The Edcor does get hot, but not as hot as you describe. After a couple of hours I can hold my finger on it indefinitely but not without a grimace. As soon as my unheated basement warms up some (7F in Georgia this morning) I'll take an actual temperature measurement.
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Old 7th January 2014, 11:39 PM   #6
pbkrag is offline pbkrag  United States
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I put in a new rectifier and it seems to be running a little cooler now. The first one I had was a new sino 5AR4, but I guess it was a little suspect. It flashed the first time I used it in my SSE. The others a 5v4 and 5u4gb were old ones (5v4 is about 70yrs old) I got off ebay. Never a problem w/my SSE but maybe an issue in the TSE. So, I got some new Sovtek 5ar4s in the mail yesterday. after about 2-3 hrs running tonight It's hot but it takes closer to 7 or 10 sec with my finger on it before the pain gets close to unbearable. So I guess I'm running in the normal range. Thanks for your responses.
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