just call it 2 phase

Michael A. Terrell wrote:


You are throwing up a problem that didn't exist because efforts to cure other problems, which were far more apparent to the operators at the time, incidentally took care of this. For a large DC generator, there would be serious performance problems with arcing (not arching) brushes- particularly under load. In extreme cases, the whole commutator could be involved- not good. First of all, brush resistance and width are designed so that current reversal (which occurs only in the coils under commutation) and is completed before the shorting of the coils in which the current was reversing was completed. In addition, at the time that this switching takes place the voltage induced in the shorted coil is near zero- the combination means no arcing. However as load changes the "neutral axis" of the machine shifts which could lead to arcing. To take care of this, the brushes of early machines could be moved to a position where arcing ceased. In later machines, interpoles were used - which added a load dependent flux in the coils under the brushes to counter this (armature reaction) effect. These replaced manual compensation about 1915-25- prior to mains powered radios. Where you get arcing and interference is where you have poorly maintained commutators and brushes, or, for cost savings, no interpole compensation or brush adjustment compensation. Where do you get this? Mainly in small and cheap "universal" (DC series) motors which can produce a lot of hash (worse on AC). The larger machines, where it was important to provide compensation would not have failed the EMI/RFI standards if they had existed at the time.
N.B. I have run multiple unfiltered 5-10HP DC motors and generators in labs in a building (without any problems with radio or near by labs depending on RF and electronics). If any sparking (as opposed to arcing) occurred, the commutator was cleaned and the brushes checked or replaced. I have been in plants where much larger DC generators are used without any problems with RF. On the other hand, I have also run into problems with a simple small 12V DC motor completely messing up radio control (incidentally, the motor was fed from an automotive battery).
The "pulsing DC" (and you are right about this being ridiculous) is something that did not occur except possibly in machines designed on the basis of "build your own DC motor" in children's "explore physics" books.
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wrote:

One of the largest universal motors must be the traction motors that an E-Lok (electric locomotive) has. It's 4 motors of 1 MW each, series, supplied with 700 V max, ac, 16 2/3 Hz. Newer technolgy allows them to be supplied with 50 Hz. Cetenary is 15 kV 16 2/3 Hz (old lines) and 25 kV, 50 Hz (newer lines). The AC motors have special construction to avoid arcing etc., which under these conditions would be destructive. Excitation for a 300 MW, 21 kV, 10 kA, alternator, is 220 V, 1000 A, DC. The rings that supply the DC to the alternator, are big as bricks, and usually, there's another shunt DC generator, on the same shaft, to excite the excitation (shunt DC) generator, and usually, there's also a tacho, too.

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On Wed, 25 Mar 2009 07:57:52 -0400 Michael A. Terrell
| A lot of transformerless tube radios were sold as AC/DC, and wouldn't | have worked if it was a Phil claims. You just had to make sure the | power plug was inserted the right way, or you got no B+ for the tubes.
And these were plugged into Edison's DC system?
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wrote:

That would do it. Did you ever work on one of those radios?
The tube heaters were in series. The filament voltages would add to 117VAC. Sometimes, if those voltages did not add up quite right, the power cord included a resistive conductor to adjust for a lower voltage string. On ac operations, the filter input capacitors would charge up to approximately the ac peak at about 150V from a half-wave rectifier. This meant that 60Hz ripple had to be filtered. To save money, there would be a resistor of about 100 to 200 ohms separating sections of a dual electrolytic capacitor. IIRC, the capacitor sections were about 20F (microfarads if you cannot read).
I never actually operated one of these sets because I always lived where ac was supplied. I did work in a place where they had dc powered sewing machines. I vaguely remember radios working there. The B+ voltage on dc operation would be lower than for ac operation.
As an aside, IIRC, the dc motors were switched on and of by the operators. Where only ac was available,the motors ran continuously. The operator operated a clutch that connected mechanical power to the sewing machine.
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Salmon Egg wrote:

Yes, some of them. Edison's system did not vanish overnight, fragments of it lasted well into the era of the transformerless AC/DC radio. As mentioned in a previous post, there were buildings in part of NY that were still supplied with DC until just a few years ago. One of the advertised features of these radios is that they could be run on either AC or DC current which was not the case with the safer and more expensive transformer sets before them.
Useless but related trivia, the band AC/DC got their name from the label on the back of just such a radio.
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James Sweet wrote:

You are right However, in most areas, these were not supplied from DC. I fear that the main purpose of these sets (with filaments in series,etc) was not to make them useful for both AC and DC service ( advertising was a side issue at the time that they were popular -40's to early 50's -they came in to being long after most systems were AC) but to eliminate the cost and weight of transformers as you indicate. Cheap sets- with reversible plugs and no separate chassis grounding- did their share in reducing the gene pool (smashed case, put it in the garage or shop- good case, perch it on the bathtub).
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Don Kelly wrote:

Sure that was the whole reason they existed, the "all-american five" tube lineup as they were commonly called, transformerless series string set was a masterpiece of cost reduction. The fact that they could be operated on either AC or DC current was simply a useful side effect of that which was marketed as a feature. Nevertheless, it was a side effect that some people did make use of.
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I got my start in electronics/electricity partly by studying/dissecting such radios. They were in fact, AC/DC, they had polarized plugs (at the time they and transformerless TVs were the _only_ thing with polarized plugs, nowadays almost everything has them).

I still remember some of the tube numbers many of those radios used. They had three 12V filament tubes (something like 12AT7 or 12AU7 for at least one of them), a 50C5 audio amp and a 35W4 rectifier. The voltage on this actually adds up to 121V, although the nameplate specified 117V AC/DC.
On ac operations, the filter input capacitors would charge up to

Yup.
These radios were the cheap consumer desktop radios before the transistor radios took over.
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They truly are a masterpiece of minimalist engineering. They cut every corner that could be cut in the name of reducing the cost. Packed components into the chassis however they would fit, wiring is a rat's nest, little in the way of shielding, and yet they do work, pretty well even, and many are still going fine a half century longer than they were intended to last.
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James Sweet wrote:

I built one of these a bit over a half century ago- worked well. The next was a Heathkit unit that worked better (and the "paint by numbers" instructions were such that the "rats nest" situation didn't occur -if they were followed).
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Don Kelly wrote:

I built my first Heathkits over 40 years ago, starting with a couple VTVM kits. I bought one and built it. My uncle saw it, and ordered one, but decided I should build it while he talked to my dad for an hour.
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On Tue, 31 Mar 2009 23:56:33 -0400, "Michael A. Terrell"

I built one of them, then a SB301(?) Ham receiver. Only one mistake. The instructions for connecting both sides of the IF filter looked the same so I skipped one of 'em. Didn't work so well that way.
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krw wrote:

RF does like a complete circuit. :)
Just be glad that you didn't have to build and tune your own tubular filters. Microdyne used dozens of different filters, but some were too small to interest an OEM, so we built them in house. It was a nightmare breaking in a new assembler. :(
When I started working there, they used sweep generators and diode detectors, then switched to network analyzers for alignment.
I built a few Heathkits that were shipped with those 'Molex pins' for the ICs. I used real sockets, instead.
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On Wed, 01 Apr 2009 06:08:17 -0400, "Michael A. Terrell"

It was a crystal, so not much chance of that. ;-)

Depending on the pins, they're a lot better than many sockets. The machined *round* pins were quite good sockets. Of course there were sockets (notably from Augat) that used the machined pins, as well. Sockets with the stamped square pins were more bother than they were worth. I threw out the set that came with a Lear Seigler terminal I built and substituted the Augat sockets.
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krw wrote:

The molex 'pins' were cheap crap that came on a reel, and were cut to length. Then you plugged the IC into the strips & soldered them to the PC board before breaking off the carrier strip. It was almost impossible to solder them by hand, without wicking the flux into the contact area. They were designed for wave soldering, and you were lucky to pug an IC in two or three times before one broke, or became intermittent. You might as well have just bent the pins over on the back of the board & not bothered to solder them.
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Michael A. Terrell wrote:

You are showing my age!! Any Heathkits I built had tube sockets (small and large). They also had big heavy transformers and nasty voltages. They did give a good product for a decent price and some ability to read and follow instructions (and solder properly-). A good way to get a decent radio and audio amp as well as basic test equipment at a decent price. Sure their scopes weren't up to Tectronics but in many applications that didn't matter when budgets had to be stretched.
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Don Kelly wrote:

I built a lot of tube Heathkits, as well. A lot of hams would buy them, and chicken out after they opened the boxes. I would quote them a high price, because I was busy with my industrial electronics customers. I also told them it would be at least a week to try to put them off, but they would just pull out a handful of bills and count them out. Most took less than an evening to assemble. :)
As far as working with large tubes, I worked as a broadcast engineer at several UHF TV stations. Those 65 KW EEV Klystrons are BIG. :)
The early Heathkit test equipment was good enough for radio & TV shops of the day, but couldn't be used for lab work, since there was nothing for a metrology lab to certify them to.
I bought a Leader LBO-505 scope in the early '70s. It was a solid state scope with excellent triggering, and used it till it was stolen about 10 years later. It wasn't anything near the Tektronix 2465B I used at my last job, but it did everything I needed at the time.
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wrote:

Reminds me of my own old Telequipment 555 true dual beam scope with 2 dual beam plugins...to make it 4 beams in all. Along with the seperate power supply one sure didn't need a heater in the lab in the winter. Loved Heathkit stuff...I have fond memories of their shop in Tottenham Court Road, London during the '70's.
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That brings back memories. The last electronics shop in Tottemham Court Road was Proops, which probably went around 20 years ago. Those electronics shops all got replaced with PC shops, and now gadget shops. Same thing happened in Edgeware Road, except I think Henry's is still there (not been there for a long time though).
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Michael Moroney wrote:

A lot of them were sold new for under $10.
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