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MC225 transformer heat

Alfmonster

Alfmonster

Active Member
Other MC225 owners, how hot does the transformers on your mc225 get during 6 hours of use? Mine stays warm to the touch for about 3 hours - Anything beyond that it gets hot. At around 6 you can still touch the transformer for a little bit - but can’t leave your hand on it like you could at 3hours.

I just had the unit gone through and repaired by AudioClassics a few weeks ago — is this an issue that should be looked through again or is this a known characteristic to the mc225 like the transformer in the mx110z?
 
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62caddy said:
Sounds exactly like my MC240 behaved. Normal operation is my guess.
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that’s really good to know - I was worried that mine was acting up when I read on another thread that their mc225 was completely cool to the touch after 6 hours.
 
Alfmonster said:
that’s really good to know - I was worried that mine was acting up when I read on another thread that their mc225 was completely cool to the touch after 6 hours.
Click to expand...

I'd check with A/C to be certain but cool after six continuous hours sounds almost incredible...

FWIW - MAC1500 PT also gets toasty hot after a few hours before and after being refurbished at A/C.
 
62caddy said:
I'd check with A/C to be certain but cool after six continuous hours sounds almost incredible...

FWIW - MAC1500 PT also gets toasty hot after a few hours before and after being refurbished at A/C.
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SaturationPt said:
Agree with caddy, my MC240 and MC75s get fairly warm after a long listening session, being next to the power tubes doesn't help.
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I figured this was probably a normal thing- specially after getting looked over. Kind of wondered about the claim that it would stay cool after 6hours. But thank you for confirming that my MC225 is not acting up.

Does this kind of heat wear on the longevity of the transformers at all? I worry that the PT in either the 110 or the 225 will go out one day.

Also good to know that the PT heating up like that seems to be across the board with the Vintage Mc tube gear.
 
I think it would be common knowledge long ago if it was an issue. Only heard of one case in an MX110. Supposedly they kept the same PT used in the early 110 that did not have 6D10 tube in the tuner which the Z version had and resulted in more heat due to the extra draw.

BTW- DOB recounted a tale of an MC240 that had been on continuously for twelve years that was brought into a Mc Clinic. All it needed was a set of output tubes and a pair of voltage doubler capacitors to bring it back to spec.
 
Maybe I’m stating the obvious, but the transformer is doing work, and not at 100% efficiency, the result being heat. The higher above ambient, the more heat dissipates.

Even at very low output my MC240 tends to equalize at a temp that is uncomfortable to the palm of my hand. After that it never gets hotter. I don’t remember the temp, haven’t run it in a long time, but you should use a thermometer (IR is easiest) and provide a number for any real diagnosis or it’s just speculation that this is normal.
 
62caddy said:
I think it would be common knowledge long ago if it was an issue. Only heard of one case in an MX110. Supposedly they kept the same PT used in the early 110 that did not have 6D10 tube in the tuner which the Z version had and resulted in more heat due to the extra draw.

BTW- DOB recounted a tale of an MC240 that had been on continuously for twelve years that was brought into a Mc Clinic. All it needed was a set of output tubes and a pair of voltage doubler capacitors to bring it back to spec.
Click to expand...

that’s amazing. A testament to the build quality of these pieces!
 
SaturationPt said:
Maybe I’m stating the obvious, but the transformer is doing work, and not at 100% efficiency, the result being heat. The higher above ambient, the more heat dissipates.

Even at very low output my MC240 tends to equalize at a temp that is uncomfortable to the palm of my hand. After that it never gets hotter. I don’t remember the temp, haven’t run it in a long time, but you should use a thermometer (IR is easiest) and provide a number for any real diagnosis or it’s just speculation that this is normal.
Click to expand...


Thanks for explaining this! Yeah I did a measurement once with an IR temp gun and more recently with my hand and noticed that it got to a certain temp but never surpassed it. It’s good to know this is considered stable.
 
Hello

is this an issue that should be looked through again or is this a known characteristic to the mc225 like the transformer in the MX110Z ?

The problem with some MX110Z causing overheating of the power transformer is caused by defctive selenium diode bridge starting to leak . Make power consuption test with selenium bridge and then with silicon bridge and you will see the difference !
The big problem with this selenimu bridge is there is no fuse and this bridge will dammage for ever your power transformer if you do not replace it .

I have made many MC240,MC75, and MC225 , none was to much hot when I touch them after many hours of use .
If you can't touch the power transformer with your hand that mean that the temp inside the transformer's can is to high and a serious check of your amplifier is necessary . Generally problems are coming from power supply .
 
Perhaps the purchase, and connection of a inexpensive KiloWatt brand plug in AC power monitor that will reveal the power consumption of the amplifier so as to be compared to the factory specs idle wattage, current, if concerned..

At least that would be a good starting point .

I power consumption/thermally monitor every one of my customer`s & my personal electronically restored tube amps on my bench for quite a few hrs. (sometimes all day)before releasing them for their installation & use.

There also may be high line voltage at the OP residence, that will raise the MC 225`s power transformer, & the tubes heat because of elevated filament voltage !!

Sadly, unlike most of the other vintage Mc. tube amps, the MC 225 has no 126 volt transformer primary tap to help with todays modern higher line voltages compared with the lower line voltages(110~117) of yesteryear in which these amps were designed.

Many yrs. ago I changed my MC 225`s original factory thermistor, when it failed, to different one that put that amp`s tube filament`s voltage closer to the design levels when the amp was plugged into 120v, and the mains that feed my sunroom`s SS/tube equipment is regulated via a Tripp Lite 20amp rated AVR..

If this is the reason of the OP`s MC 225 running at elevated temperatures, he might wish to look into a properly sized bucking transformer to tame elevated mains voltages at his residence, if that is common situation..

Just some suggestive noise from me, folks, carry on...

Ciao
 
Don't forget also that noisy power, ... if there's something nearby that is using power to run lots of flourescent lights, big pumps, etc. it can cause more heat in the power transformer as transformers like clean sine-wave power.
 
What will be very interesting would be to measure the power comsuption of each secondaries of the power transformer .

I have no doubt that you will give us lower values than the owner of the very hot one !
 
I ran my MC75s for about 8 hours yesterday afternoon / evening, efficient speakers modest volume, when I shut it down last night it was uncomfortable to leave the palm of my hand on the PTs (both felt exactly the same) but not painful. I'll have to measure them next time to quantify "uncomfortable but not painful", but that's about how I would characterize my MC240 PT after several hours also and the 240 measures perfect everywhere under the deck.

However, I have seen photos under the deck of McIntosh tube amps where there is some tar/potting drooled down the transformer wires, these are the ones that would make me very concerned, I believe that tar is pourable around 200*F, which would be much more than painful!
 
clinic-audio said:
Hello

is this an issue that should be looked through again or is this a known characteristic to the mc225 like the transformer in the MX110Z ?

The problem with some MX110Z causing overheating of the power transformer is caused by defctive selenium diode bridge starting to leak . Make power consuption test with selenium bridge and then with silicon bridge and you will see the difference !
The big problem with this selenimu bridge is there is no fuse and this bridge will dammage for ever your power transformer if you do not replace it .

I have made many MC240,MC75, and MC225 , none was to much hot when I touch them after many hours of use .
If you can't touch the power transformer with your hand that mean that the temp inside the transformer's can is to high and a serious check of your amplifier is necessary . Generally problems are coming from power supply .
Click to expand...


This is so interesting - how do you test for a defective selenium diode? Also is this a normal procedure that is done when most of these units are being restored? @62caddy do you know if this is a standard restoration process at AudioClassics?

thank you for this reply!
 
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