Remember that the dual-power locomotive transformer handles about ten-to-fifteen times the power of an mu-car transformer. This is in addition to the weight and size required for the 25Hz capabiklity
Locomotive transformers were not considered as all manufactured for this country are dual frequency dual voltage motors. Now if you consider overseas the UK 50 Hz transformers would be close but not exact.
Just for grins. If the NEC including SEPTA is ever (?) converted to 60 Hz would replacement transformers be smaller ? Although only if dave and I live to be 200 years would we see it happen..
A couple of more notes on multifrequency transformers.
The upper frequency limit for transformers using laminations is set by eddy current losses in the laminations, with limit efined by how much eddy current loss is tolerable. The approx 500VA transformer in my Crown D-150 amplifier was stated by Crown to work at 50, 60 and 400Hz, though the transformer may be on the upper limit of acceptable operation at 400Hz. High frequency transformers typically use nonconductive ferrites for the magnetic material.
Designing a good High Fidelity Audio transformer is not a trivial undertaking, with about a 1,000:1 range in frequencies (hats of to Dave on that). Tricks used in design include high-mu magnetic material (eg. mu metal, permalloy) and layered windings. One reason that Crown and other manufacturers went to direct coupled amplifiers was to get around the difficulty of dealing with output transformers.
Power transistors are inherintly low-impedance devices, and so direct-coupling is possible. High-powered output vacuum tubes are (were -- although I understand there are still hi fi fans and manufactureres who swear by tube amplifers, the remaining distortion is supposed to be more tolerable and pleasant to their ears than transistor amps. I confess I don't hear the distoriton in either type.) are inherintly high-empidance amplfiers, and so transformers were esssential. (I suppose you could put a 50 plus 50 6L6 output tubes in push-pull-parallel to drive one 16-ohm loudspeaker.)
In addition to being low-impedance, transistor audio amplifiers have the advanages of greater efficiency, much lower heat production, far more compact and less weight. Greater cleverness is required to control distortion, but this is a solvable design problem. Also, transistors can seem to last indefinitely, whereas vacuum tubes needed replacement, much like incandenscent bulbs. This was particularly true of output tubes. The technlogy has progressed where multi-driver loudspeaker systems, with specific loudspeaker elements to cover specific ranges, and perhaps several for each range to shape directional characteristics, can have one power amplifier for each speaker element, and then frequency response and even microsecond delay opmtimized for the purpose of that particiular driver, with the whole shebang coming from the digital to analogue converter right at the loudspeaker system, and the whole audio system between there and the microphone, inlcuidng condtrol, digital. Not very possible with vacuum tubes!
daveklepper (I suppose you could put a 50 plus 50 6L6 output tubes in push-pull-parallel to drive one 16-ohm loudspeaker.)
Nice in winter but the summer air conditioner bill would be a problem.
Electroliner 1935 daveklepper (I suppose you could put a 50 plus 50 6L6 output tubes in push-pull-parallel to drive one 16-ohm loudspeaker.) Nice in winter but the summer air conditioner bill would be a problem.
I had an uncle who was an EE at Lockheed for a couple decades after working at radio and TV stations for a decade and a half. One of his projects was making a direct coupled tube amp, one probelm with it was that the output would drift close to one of the supply rails until a loud segment of music came on and it would go back to center.
One way to deal with the load impedance issue is to wire a bunch pf 16 ohm speakers in series...
Dave's right about transistors' low impedance making direct coupled outputs possible. It did take a bit of breaking away from tube design with the use of bipolar power supples instead of single ended supplies to get away from output capacitors. That and some nifty tricks in current limiting for the output transistors.
Now for something a bit more on topic for the forum...
I was browsing through the "Wolfspeed" (Cree's RF and Power division) website and came across a paper on three phase inverters for motor applications. They were claiming that an inverter running running at a 5 kHz switching frequency and producing ~60Hz output was doing so with what looked to be 99.2 to 99.3% efficiency when supplying a 50HP motor at full load, where the best standard silicon inverters were barely touching 99% efficincy. If a 0.3% improvement in efficiency doesn't sound like much, consider that a 40KW inverter would pump out 400W of heat with silicon and 280W of heat with SiC. The weight of the electronics is just a few pounds (the module with 6 SiC FET's weighs about 1/2 lb), dominated by the DC link capacitors and the heat produced is probably about what my uncles direct coupled tube amp put out.
- Erik
My late father was a clerk on the LIRR from 1963 through 1983 and worked for some time in the Ticket Receiver's office in Penn Station. Often those FL9s would run through the tunnels and into Penn Station on diesel power, the rules be damned. They wouldn't shut the prime mover down for fear that they wouldn't be able to restart it. I personally experienced the stench and the haze of their exhaust, on more than one occasion, as a commuter on the LIRR. The same applied over at Grand Central Terminal. The steam boilers on the GG1s were supposed to be shut down too, from the Bergen Hill portals through Long Island City, but very often weren't.
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