HOT Iron ?

Vespasian · 1st November 2006, 12:32 AM

After being powered up for an hour or so, how hot should an output transformer get? Can't keep my palm down on my early 60's Scott for more than 3 or 4 seconds.

Thanks again, Ed

Wavebourn · 1st November 2006, 12:39 AM

Quote:

Originally posted by Vespasian
After being powered up for an hour or so, how hot should an output transformer get? Can't keep my palm down on my early 60's Scott for more than 3 or 4 seconds.

Thanks again, Ed

Usually power transformers are calculated by overheating or voltage loss. So, it is usual for them to be hot. It may be too hot if designed for 115V when you have 130V, it may mean a core saturation. Also, your output tubes may be biased too heavy.

I don't know if it is the case, I hope I might help.

Vespasian · 1st November 2006, 12:44 AM

So... based on the 3 or 4 second statement above, does that sound too hot to you? I've got 122v here... Thanks for your input Wavebourn.

Cheers, Ed

jaymanaa · 1st November 2006, 12:52 AM

Most of mine get that hot, at least on the store bought stuff.

sorenj07 · 1st November 2006, 01:11 AM

a quick fix is to slap a thermistor or two on the transformer's primary winding. dual benefit: slow start, and a bit of a dropped voltage

DigitalJunkie · 1st November 2006, 01:45 AM

Power trannies usually run warm/hot..
Output Transformers,IME,Don't usually run HOT,or even very warm... you might want to check the bias and whatnot,and make sure the amp isn't oscillating.

HollowState · 1st November 2006, 02:23 AM

Hi Ed,
You did say and mean output transformer? I concur with DigitalJunkie. An output transformer should not run very hot, even after many hours of operation. Most of their heat comes from what is absorbed from the nearby tubes and power transformer. If you can't keep your hand on it for more then a few seconds, it's up around 125º F or more. And that's too hot. Do scope the output for ultrasonic oscillation.

Victor

refference · 1st November 2006, 02:28 AM

Hi Vespasian ,

OUTPUT TRANSFORMER don’t run hot , by itself .
You need to check at least 4 points :

1) If the power amplifier is oscillating ( as said above )
Use a scope .
2) If you have a biasing problem ( as said above )
Check the values
3) Check the negative feedback network ( capacitors ,
resistors , etc.)
4) You probably have a defective output transformer
( a short circuit between two or more turns , in the
primary and / or in the secondary windings )

Two months ago I had a similar problem with my client’s
SCOTT 240 and the solution , was to rewire the output trans-
former .

I hope it helps the troubleshooting . Regards ,

Carlos

Wavebourn · 1st November 2006, 02:39 AM

Oops... I misread, it is about output transformer. Too much bass too loud may cause the similar effect.

Vespasian · 1st November 2006, 03:09 AM

Thanks everyone, - both output transformers are running hot. The amp is using 7591's. Could someone give me a step by step on how to properly set the bias? There are two pots for dc bias, and I simpy have them set so the voltage difference between the plates is 0v. The plates are at about 435 and grids are around -17, -18v. Don't have a scope...

1st November 2006, 12:32 AM	#1
Vespasian diyAudio Member Join Date: Sep 2006	HOT Iron ? After being powered up for an hour or so, how hot should an output transformer get? Can't keep my palm down on my early 60's Scott for more than 3 or 4 seconds. Thanks again, Ed

1st November 2006, 12:52 AM	#4
jaymanaa diyAudio Member Join Date: Jan 2006 Location: Kansas	Most of mine get that hot, at least on the store bought stuff. __________________ "Make everything as simple as possible, but no simpler" Einstein

1st November 2006, 02:39 AM	#9
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Oops... I misread, it is about output transformer. Too much bass too loud may cause the similar effect. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

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1st November 2006, 12:44 AM	#3
Vespasian diyAudio Member Join Date: Sep 2006	So... based on the 3 or 4 second statement above, does that sound too hot to you? I've got 122v here... Thanks for your input Wavebourn. Cheers, Ed

1st November 2006, 01:11 AM	#5
sorenj07 diyAudio Member Join Date: May 2006	a quick fix is to slap a thermistor or two on the transformer's primary winding. dual benefit: slow start, and a bit of a dropped voltage

1st November 2006, 01:45 AM	#6
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	Power trannies usually run warm/hot.. Output Transformers,IME,Don't usually run HOT,or even very warm... you might want to check the bias and whatnot,and make sure the amp isn't oscillating.

1st November 2006, 02:23 AM	#7
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	Hi Ed, You did say and mean output transformer? I concur with DigitalJunkie. An output transformer should not run very hot, even after many hours of operation. Most of their heat comes from what is absorbed from the nearby tubes and power transformer. If you can't keep your hand on it for more then a few seconds, it's up around 125º F or more. And that's too hot. Do scope the output for ultrasonic oscillation. Victor

1st November 2006, 02:28 AM	#8
refference diyAudio Member Join Date: Jan 2006 Location: SAO PAULO - SP	Hi Vespasian , OUTPUT TRANSFORMER don’t run hot , by itself . You need to check at least 4 points : 1) If the power amplifier is oscillating ( as said above ) Use a scope . 2) If you have a biasing problem ( as said above ) Check the values 3) Check the negative feedback network ( capacitors , resistors , etc.) 4) You probably have a defective output transformer ( a short circuit between two or more turns , in the primary and / or in the secondary windings ) Two months ago I had a similar problem with my client’s SCOTT 240 and the solution , was to rewire the output trans- former . I hope it helps the troubleshooting . Regards , Carlos

1st November 2006, 03:09 AM	#10
Vespasian diyAudio Member Join Date: Sep 2006	Thanks everyone, - both output transformers are running hot. The amp is using 7591's. Could someone give me a step by step on how to properly set the bias? There are two pots for dc bias, and I simpy have them set so the voltage difference between the plates is 0v. The plates are at about 435 and grids are around -17, -18v. Don't have a scope...

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