Question What is the expected lifespan of a transformer?

[BarefootGuy]

Hi folks,

I love my vintage Quad amplifiers, especially my 303 and 306. Obviously, one component of a power amplifier that can become faulty is the transformer. I managed to purchase a "new old stock" 306 transformer directly from Quad, just in case mine develops a fault in the future, as I am rather hoping the amp will last another 30 years with careful, regular servicing. But what about the 303? Some are already about 50 years old and I am thinking maybe I should buy a spare transformer, just in case. But then I thought, maybe I am being silly and spending money unnecessarily?

So, my question is, how long do transformers in home stereo amps last?

Many thanks in advance for any advice offered.

 

[awkwardbydesign]

Forever, if not overloaded.

 

[BarefootGuy]

Forever, if not overloaded.

Well...forever sounds pretty good to me. If that is the case, can I ask what "overloaded" means?

 

[bigrod]

I’ve got half a dozen quad amps 40 + years old and still going strong

 

[Beobloke]

To be fair, I’d rank a transformer as very near the bottom of the list of “things to worry about” unless a specific type of fault occurs.

I’ve only ever had one fail - that was in a phono stage and one of the rectifier diodes in the PSU went short circuit. This pulled excess current through the transformer, which overheated, melted its insulation and finally shorted its wiring to the earthed case, tripping the house RCB.

I repaired it with new diodes and a new transformer, and added the protective fuses that the designer should have fitted in the first place.

 

[slavedata]

The thing to worry about in Valve amplifiers is a dodgy output valve shorting ,suddenly taking very large current and taking out the output transformer. In my Fisher 500C when I renovated it someone suggested fitting small 10 ohm resistors between the cathode? and ground. If there is a sudden rush of current the resistor smokes cuts out and the transformer is protected. it's saved the output transformer for me and as these are unobtanium these days it's a better solution.

 

[rabski]

'Overloaded' means run in execss of its specifications, such as too high an input voltage or too large a current drain on the secondary windings.

Run a transformer under its stated current and it will effectively last as near to forever as makes no difference.

I've had two failed ones come though here. One on an early Leak Stereo 20, before the changes to avoid the output stage failures. That one had most likely been left powered up with a serious failure. The other was in an old guitar amp, and looked as though it had been replaced in the past with something non-standard and woefully underrated for the heater current.

 

[BarefootGuy]

'Overloaded' means run in execss of its specifications, such as too high an input voltage or too large a current drain on the secondary windings.

Run a transformer under its stated current and it will effectively last as near to forever as makes no difference.

I've had two failed ones come though here. One on an early Leak Stereo 20, before the changes to avoid the output stage failures. That one had most likely been left powered up with a serious failure. The other was in an old guitar amp, and looked as though it had been replaced in the past with something non-standard and woefully underrated for the heater current.

Hi Rabski,

Thank you for your reply. I assumed this is what overloaded means but didn't wish to assume incorrectly. Perhaps the 303's transformer will be fine then, although I am sure there are other things that can go wrong with them

 

[Alister M]

In all my years in the electronics servicing trade, I can only remember changing about 3 transformers. One was a lightning strike, one was shorted turns on the primary winding and one an open circuit secondary. So to answer your question- they tend to last forever!

 

[Bianchennero]

there is nothing eternal. If they are not underpowered - which is impossible unless it is a home-built amplifier - they last a lifetime. I can think of a possible oxidation of the steel lamierins, if present, or of the winding, but this is still a very remote problem and can affect the entire device.

 

[bigrod]

Early Quad stuff was designed and made to be bomb proof .
Not so sure about newer models made outside the Uk ..

 

[gyurmaember]

Forever, and if they gone, they're still repairable or replaceable with and off the shelf model.

 

[toprepairman]

Currently have a Ming Da pre in for repair with a faulty transformer.
Also had a Minimax pre with a faulty tx a little while ago.
Chinese kit is built for 220 Volts. They often put 230V stickers on thinking 'oh that'll be alright' little realising it can be subjected to up to 253V here.
Never had a 303 or 306 with a duff tx so no need to hold spares for those or most other UK built kit.
The Minimax was running 3 or 4 valve heaters but on inspection the winding had wire so thin it was only suitable for a small light bulb, can't help thinking they will all fail in due course.
Americans also tend to think we're on 230V so a lot of their kit (even very prestigious stuff like Conrad Johnson and AR etc.) is running beyond their limits. They do break down more than they should as a result.

 

[joleyami]

Hi folks,

I love my vintage Quad amplifiers, especially my 303 and 306. Obviously, one component of a power amplifier that can become faulty is the transformer. I managed to purchase a "new old stock" 306 transformer directly from Quad, just in case mine develops a fault in the future, as I am rather hoping the amp will last another 30 years with careful, regular servicing. But what about the 303? Some are already about 50 years old and I am thinking maybe I should buy a spare transformer, just in case. But then I thought, maybe I am being silly and spending money unnecessarily?

So, my question is, how long do transformers in home stereo amps last?

Many thanks in advance for any advice offered.

Something like an older Quad (Or most Uk, USA, Jap older kit) should have good quality Varnish on the Windings.
I've never had a failure, unless the Transformer has got insanely hot.
I cannot vouch for the quality of Chinese Varnish, or even water based products that are used today.
As stated, an older transformer should last for a few hundred years if used as intended.

 

[Radioham]

There are many Transformer in excess of 75 years old still working well. It depends on how well they were designed and made. Transformers made in the UK have a reputation for being well made.

The are a couple of parameters which can affect the life, one is the transformer temperature. The transformer is made from wire which has an enamel coating, some can withstand higher temperatures before breaking down. The other is the volts per turn on the windings. Each winding will have a different voltage to the adjacent turn. The lower the volts per turn will give a longer life, but uses more wire and occupies a larger space for the same voltage, Typically some of the Chinese products run their transformer very hot.