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The dumbest thing I've ever seen in amp construction....
The dumbest thing I've ever seen in amp construction....
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Old Yesterday, 12:58 PM   #41
Tubelab_com is offline Tubelab_com  United States
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Location: West Virginia panhandle
I bet the new tires are "thinner"
They are actually wider since traction was a big issue with a bunch of weight hanging out behind a front wheel drive vehicle. My past involved a bit of automobile racing, and my main intention was to increase the numerical final drive ratio as much as possible with the original 16 inch wheels. I got 7% which made a difference. The optional wheels for the Element are 18 inches, which is a step in the wrong direction.

Back to the transformer discussion, I have been using Allied Electronics power transformers since the 1970's in my vacuum tube amps. They have always been made by Hammond in Canada. Of course the price for the big 6K7VG has gone from the $20 range then to over $50 now. The physical size has remained the same but they have been on a steady diet over the years. The oldest that I have on hand is from the late 1990's. It weighs a few ounces more than a new one and runs a lot cooler.

I believe that the new ones use modern materials which shrug off the higher temps so that some tradeoffs can be made in the iron and copper department. I have one of those in an SSE amp that I built in 2005 and I routinely suck 200 to 220 mA (60 Hz power) from a transformer rated for 150 mA at 50 Hz. It gets too hot to touch after several hours but has been reliable. The amp was the power for my Yamaha NS-10 "computer Speakers." For several years that amp was on for several hours a day.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old Today, 08:02 AM   #42
Gnobuddy is offline Gnobuddy  Canada
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Since I stumbled into this thread, I've been wanting to find some trustworthy quantitative data to settle the whole argument about transformers with welded corners.

As I said earlier, the answer is to be found in Maxwell's equations, and a suitable software program that uses them to model flux density in a transformer core.

I found out that Solidworks (a very popular 3D CAD program normally used to design mechanical parts) also does magnetic flux simulations. The attached image shows a simulation of the magnetic flux inside a conventional E-I core. (Not my simulation, I found this on the 'Net here: Open & Short Circuit Transformer Simulation Tests inside SOLIDWORKS )

Long before computers and FEA (finite element analysis), scientists used a simple concept called "magnetic lines of force" to try to visualize and describe magnetic fields. It is not quantitative or exact, but the imaginary "lines of force" were found to have certain properties that always seemed to hold.

One of those properties is that the lines do not "like" to make sharp bends, and so I was almost certain, based on this old nineteenth century visualization aid, that the outside corners of a transformer core would have relatively low magnetic flux density. The lines of force would not travel right to the corners of the core.

I was right, but I did not anticipate just how dramatic the effect would be. Leaving the nineteenth century aside, let's look at the Solidworks simulation, a very 21st-century way to look at the same problem of magnetic flux density in a transformer core, but this time with considerable accuracy.

Look at the image closely. According to the scale on the right side of the image, the red areas correspond to a flux density of just over one Tesla. Meantime, the outside corners, in dark blue, correspond to a flux density of about 2.6 x 10^(-5) T.

That's 0.000026 Tesla. Which is thirty eight thousand, four hundred and sixty two times weaker than the 1 Tesla flux near the centre of the core.

Eddy currents are driven by the magnetic flux. If the flux is nearly forty thousand times weaker at the corners, so are the eddy currents there.

In other words, there is so little magnetic flux at the corners of the transformer core that you could weld them all solid, and it would make a negligible difference to the transformer.

Peavey's decision to weld their transformer corners was not stupid at all.

The microwave oven engineers who specc'd welded transformer corners are not stupid, either.

The worst we can say about these welded cores is that they make life difficult for DIY transformer rewinders. True, but hardly a unique case; manufacturing has been moving towards non-repairable products for a long time now. My entire Fender SuperChamp XD guitar amplifier was described as "not serviceable" by Fender Corp themselves - they want you to pitch it in the recycling bin if it ever stops working.

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File Type: jpg solidworks_tranformer_magnetic_flux_density.jpg (54.3 KB, 50 views)
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Old Today, 08:15 AM   #43
Kay Pirinha is offline Kay Pirinha  Germany
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Thanks, Gnobuddy!
This clearly visualizes that every participant in this discussion was right - besides the OP ! It also visualizes why double C or quadruple C cores are superior by far over EI cores, though saving iron masses.

Best regards!
"Bless you, Sister. May all your sons be bishops." (Brendan Behan)
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Old Today, 08:49 AM   #44
DF96 is offline DF96  England
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When I saw the picture in post 1 my immediate thought was "why have they put the OPT right next to the input valve?". This seems to be asking for instability, which then has to be killed off with huge grid stoppers, which then provide scope for 'tube rolling' (which is actually an inconvenient form of tone control).
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Old Today, 09:21 AM   #45
edbarx is offline edbarx  Malta
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Magnetic hysteresis is a well know effect. Any Advanced Physics text book explains it.

Transformer Losses
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Old Today, 10:45 AM   #46
JMFahey is offline JMFahey  Argentina
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And this flux diagram
Click the image to open in full size.

also explains:

Click the image to open in full size.

Click the image to open in full size.

both Fender Twin Reverb output transformers.
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
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