TRANSFORMERS - Let's discuss

Donnie B.

Well-known member
Mechanical engineer here. Spent a lot of time on various projects that used them and learned some stuff along the way.
Would love to hear from others.





Will try to be less cocky in the future.
 
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glpg80

Well-known member
The transformer doesn't have an impedance of its own; it only reflects a voltage (or impedance - just the square the turns ratios) from the primary winding to the secondary windings through a ratio of the number of turns of the secondary compared to the primary. Magnetic flux linkage in a ferromagnetic material due to Hopkinson's Law is why transformers transform voltage across a primary impedance, into AC voltage across a secondary impedance and subsequently into a (well matched) inductive load such as a speaker.

The amount of magnetic flux in the ferromagnetic core is dependent upon current flow within the primary coil of wire, the number of turns on the primary, and the reluctance (magnetic resistance) of the ferrite core of the transformer. That’s why the material matters for the plates that make up a EI or C core transformer. The current flow generated within the coil generates a magnetic field, which causes magnetic flux to follow the path of least reluctance. The magnetic flux then traverses through the ferrite material to the secondary windings; generating a current within the coils of the secondary through flux linkage. Voltage is then produced across the secondary terminals due to Faraday’s law of Induction.

In summary, transformers are passive lossy devices. Power in is power out minus losses. The impedance you’re changing on the secondary are strictly for maximum power transfer, stepping the primary tube impedances down to speaker load impedances. In essence, the transformer takes high voltage swings of transient plate currents from the tubes and transforms (hint, transformer) them into low voltage high current sources for the speakers.

I also want to note that there is a lot of magnetic flux stored in a transformer core - which can cause havoc to circuits when impedances are mismatched (primary OR secondary). This means mismatching secondary speakers to secondary windings reflecting an intended impedance from the plates, which may or may not be correctly matched with tube swaps to a particular transformer’s intended primary impedance, can cause transient responses which over frequency can be damaging at high volumes. Just keep that in mind.
 
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Donnie B.

Well-known member
@glpg80 are you an EE?

In layman's terms: A transformer has a primary side and a secondary side.
You put a voltage into the primary and then get a different voltage out of the secondary.

Depending on the design you can either get less voltage out (step down) or
more voltage (step up). The secondary can also be tapped to supply multiple
different voltages out at the same time.

Now, about that steel......
 

SpiderWars

Well-known member
It transforms hi voltage/lo current to lo voltage/hi current or vice versa.

The PT transforms 120vac wall voltage to 6.3vac (lo voltage but hi current) filament voltage and say ~350vac (hi voltage but lo current) B+ aka HT voltage.

The OT transforms the hi voltage/lo current tube plate power to lo voltage/hi current speaker power.
 

glpg80

Well-known member
@glpg80 are you an EE?

In layman's terms: A transformer has a primary side and a secondary side.
You put a voltage into the primary and then get a different voltage out of the secondary.

Depending on the design you can either get less voltage out (step down) or
more voltage (step up). The secondary can also be tapped to supply multiple
different voltages out at the same time.

Now, about that steel......

Yes I have a masters in EE. It’s not easy to explain their functionality at maxwells equations and physics laws, but it eliminates absolutely any chance of opinion based descriptions as to how they work and what they do. I took the time to write that on a similar topic over on TGP back in November of last year. It comes up often.
 

dirtyfunkg

Well-known member
Yes I have a masters in EE. It’s not easy to explain their functionality at maxwells equations and physics laws, but it eliminates absolutely any chance of opinion based descriptions as to how they work and what they do. I took the time to write that on a similar topic over on TGP back in November of last year. It comes up often.

Thanks for this info.

It's been about 10 years, but when I studied EE at the undergrad level, once you got through linear circuits, the whole curriculum seemed to turn very DSP and circuit logic based. Definitely not the place to learn about tubes... much more computer/computing hardware based. As soon as that became clear, I switched majors haha.
 

glpg80

Well-known member
Thanks for this info.

It's been about 10 years, but when I studied EE at the undergrad level, once you got through linear circuits, the whole curriculum seemed to turn very DSP and circuit logic based. Definitely not the place to learn about tubes... much more computer/computing hardware based. As soon as that became clear, I switched majors haha.
No problem and yes I agree there is no way to remember everything from our formal education - I keep a lot of reference material around.

My undergraduate and graduate background was centered around RF and electromagnetics.
 

psychodave

Well-known member
Donnie is a clown. Get off your high horse and stop trying to act smart and all knowing… nobody is asking or wanting your explination. 🤦‍♂️

glpg80’s response closed this bullshit thread nicely. 👍👍👍
 

Smashedguitarist

Well-known member
The transformer doesn't have an impedance of its own; it only reflects a voltage (or impedance - just the square the turns ratios) from the primary winding to the secondary windings through a ratio of the number of turns of the secondary compared to the primary. Magnetic flux linkage in a ferromagnetic material due to Hopkinson's Law is why transformers transform voltage across a primary impedance, into AC voltage across a secondary impedance and subsequently into a (well matched) inductive load such as a speaker.

The amount of magnetic flux in the ferromagnetic core is dependent upon current flow within the primary coil of wire, the number of turns on the primary, and the reluctance (magnetic resistance) of the ferrite core of the transformer. That’s why the material matters for the plates that make up a EI or C core transformer. The current flow generated within the coil generates a magnetic field, which causes magnetic flux to follow the path of least reluctance. The magnetic flux then traverses through the ferrite material to the secondary windings; generating a current within the coils of the secondary through flux linkage. Voltage is then produced across the secondary terminals due to Faraday’s law of Induction.

In summary, transformers are passive lossy devices. Power in is power out minus losses. The impedance you’re changing on the secondary are strictly for maximum power transfer, stepping the primary tube impedances down to speaker load impedances. In essence, the transformer takes high voltage swings of transient plate currents from the tubes and transforms (hint, transformer) them into low voltage high current sources for the speakers.

I also want to note that there is a lot of magnetic flux stored in a transformer core - which can cause havoc to circuits when impedances are mismatched (primary OR secondary). This means mismatching secondary speakers to secondary windings reflecting an intended impedance from the plates, which may or may not be correctly matched with tube swaps to a particular transformer’s intended primary impedance, can cause transient responses which over frequency can be damaging at high volumes. Just keep that in mind.
Wrong. It's fairies and Pixie Dust...
 

Donnie B.

Well-known member
Tell us about the metal, Donnie

Had a speaker with a distribution transformer inside that was causing the amplifier to go into protective mode too quickly.
Transformer had been in production for 10 years so 'something' must have changed. Passed all production testing. Passed
all of the visual and mechanical inspection. (you wanna go bug eyed? Try counting how many individual layers make up the
steel core of the power transformer inside your amp)

H97b41e7c131d45798e3a760ce8d877deN.jpg_.jpg


What we ended up finding out is the factory that stamped out all of the individual 'E' and 'I' pieces changed to the next lower grade
of carbon steel (less $$) without notifying anyone. The lower grade steel was saturating more easily than the original grade which would
cause the speaker to draw more current from the amp which would then put the amp into protective mode.

Transformer passed both electrical and mechanical testing and yet the steel supplier had increased his profits and no-one was the wiser
until a customer decided to really crank up a system which exposed the issue.

Next time you play an amp that mushes out too easily? Shitty steel in the core might be the culprit.
 

psychodave

Well-known member
You're mostly a good read.
Just wish you'd give the personal shit slinging a rest.

(nice touch posting all the booze to an alcoholic - was that suppose to sting or something?)
You’re mostly a good read as well, but quite often you talk down to people. There are some really smart people here and you can’t assume we are all ignorant. Had you posted something like “Let’s discuss transformers” instead of coming off as some savant trying to test people before you bestow your infinte knowledge on us, you’d be taken more serious.
 
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