PV6 : very hot power transformer

[latole]

As some of you know, I have been working on my PV6 (balance pot) recently.

I noticed that the power transformer becomes very very hot and quickly. Impossible to touch it with your fingers without getting burned,
I even removed the cover to help.

In my opinion it has always worked like this.
This is not a desirable operation.

Have you noticed the same thing on your PV6?

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[admin]

That's interesting. I'm really not sure "how hot is normal." As long as the output voltages are correct, I'm not sure what would cause the overheating (without any physical signs of damage). Best would be to take temperature readings on two PV6's and compare,... but that may be difficult.

[AnotherJohnson]

One problem with old transformers is that the insulation fails and then you get shorts across coils, or worse. This affects the effective turns ratio, or worse.

Are you getting the right voltage ratio?

All transformers do get hot. And heat accelerates aging. But what’s the right temperature? Or maximum safe temp?

I’ve read that temps as high as 120 C might be acceptable in some cases.

Maybe Roberto knows.

[admin]

Another (less accurate) but much easier to tell if it's generating an abnormally large amount of heat would be to put a power meter on the unit's power cord and compare it to another PV6. Almost all the power use is going to be heat. So if this unit is drawing twice the wattage of a comparable unit, then that would be of concern. I should note that if different tubes are being used, that could have an influence on the power draw as well.

[latole]

One problem with old transformers is that the insulation fails and then you get shorts across coils, or worse. This affects the effective turns ratio, or worse.

Are you getting the right voltage ratio?

All transformers do get hot. And heat accelerates aging. But what’s the right temperature? Or maximum safe temp?

I’ve read that temps as high as 120 C might be acceptable in some cases.

Maybe Roberto knows.

Voltage at xfr secondary are ;
red wires ; 342 AC
brown wires ; 16 AC this is the heater voltage before the regulator. IMO Regulator should send 12 DC to tubes heater.
I read voltage few weeks ago when I work on the balance control. Now PV6 is on a shelf

Do you mean 120 F not 120 C ? I read 48.5 C, this 120 F

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[AnotherJohnson]

120 F doesn’t seem inordinately hot for and old transformer.

[admin]

You should be able to touch 50 C rather easily and shouldn't burn your fingers. I've been in outdoor temperatures of 45 C. This could very well be a normal temperature.

I don't know what the spec voltages are supposed to be so I can't comment.

[latole]

You should be able to touch 50 C rather easily and shouldn't burn your fingers. I've been in outdoor temperatures of 45 C. This could very well be a normal temperature.

I don't know what the spec voltages are supposed to be so I can't comment.

50C air temperature is different from a iron 50C temperature.
Secret is heat transfert.

[admin]

That may be true. I really have never done comparisons on touching different substances at that temperature.

I will say however that an electronic component running just 15 C above ambient room temp does not seem to be worrisome to me.

[AnotherJohnson]

120 F water is not too hot for most to touch. But 130F is more than most would touch, and 140 F water is too hot for nearly all.

When I said 120 C, which is waaaay too hot for anyone to touch, being nearly 250F, I did mean C.

This sounds like a non problem if the voltages match the turns ratios and it’s not humming.

[latole]

This sounds like a non problem if the voltages match the turns ratios and it’s not humming.

You are right.

Thank's all.

[roberto]

Hola Latole,

Turn the unit off. Unplug it from the mains AC. Just disconnect the secondary wounds (probably only two pairs) and put some tape to insulate them from a possible short, and turn the unit on. If you have temperature at the transformer after one minute of being tuned it on, it is wise to replace it or send it for a rewound it. As you said, it is not normal the behaviour of the transformer. If it is working fine, then on one of the power supply circuit, you could have a bad component that it is draining too much current. Usually a bad cap could be the problem. The problem could be on one channel too. Just disconnect the bias voltage on each channel to see the behaviour of the XFR. Just guessing.

[latole]

Thank you Roberto. I will look .

[latole]

I took some voltages reading, not exactly like you write; nothing disconnected. Look all good.
Temperature look better with top cover removed.
Preamp work fine.

End of the story. Thank you all

[roberto]

Those are good news...good to know that everything is working as it should.

Happy listening latole...

[latole]

Yes, with your help and this excellent forum that my "problem" made me discover.
Thanks again for your help.