Some information on CRT’s- Honest and Accurate Unlike Much of What You Read on the Topic Elsewhere.

While this subject is a little tangential to the concepts of the blogs, it does have a place here. The subject is Cathode Ray Tubes or “CRT” for short hand. Because of the proliferation of laws recently and potentially soon to come to pass: the potential parts sources in general of salvage materials to pull parts from or repair may dry up completely. In no small part due to the misunderstandings of what is actually in many electronics and just what component may be to blame, and without specificity as to what vintage of item is of concern as well. So as a result “blanket” laws are thrown at the issue.

There is a great hue and cry over CRT’s entering the waste stream and there are “those who mean well” who only have a small fraction of the real information about them and thenapply that little bit of knowledge over the full spectrum even to where it does not belong or does not accurately apply. As a result the concerns about lead within CRT’s leads to a great deal of misinformation. This post seeks to dispell some of that ignorance with a rational discussion on the subject. Which is important because of a number of large piles of abandoned CRT’s and CRT glass being abandoned and then treated as if it is comparable to “Love Canal”.

Now, most of the CRT’s that are in the waste stream today are post 1975 vintage. And that is significant because of how CRT’s were made prior to about that year were usually made differently than those after that year, and there is some overlap in technologies. When CRT’s came on the scene for televisions after WW2, most were black and white TV sets and most were made with a metal shell. The glass face of the picture tube and the glass neck that held the electron gun were essentially bedded in a lead seal between the metal shell and glass face and the glass neck. That method was continued when the glass envelope or in scrap terminology- the “Funnel Glass” replaced the metal shell. The glass was aluminized internally, and some insulating materials were applied externally to retain the same eletrical characteristics the metal shells had, but the black and white tubes (White Phospor coating inside actually) began to be made with the neck formed with the funnel essentially being just one piece of glass, but the face was still bedded in a lead seal between the face and the funnel for a while. It was not until later technologies of late 1960’s into the the 1970’s where the face glass was fused to the funnel for the White phosphor CRTs thus removing all of the easily recoverable lead from CRT production once steel pins were adopted as well.

In the 1950’s in the US and Canada, color TV sets began to appear, RCA’s CTC1 chassis being among the first US color sets. Now the color sets incorporated 3 different phosphor colors of red, green and blue. Each color also had it’s own electron gun and in order to make sure the color gun was hitting the same color dot of phosphor on the face, there was a metal (iron) screen mask between the guns and the phorphors on the face glass. Now the important thing here is these tubes were made to be rebuildable. So much so that you could get the equipment and supplies to rebuild the CRT’s that did not have burned phosphors in your own garage. These CRT’s were made with lead bedding between the face and funnel and the neck and funnel which held the gun assembly. The “Frit” as it was called, was where the gun assembly would bed into that funnel, be it a metal funnel or glass funnel.

As color TV set prices dropped, those tubes made roughly after 1973 no longer had a “frit” and were no longer garage rebuildable. My dad actually worked with a fellow who did rebuild the CRT’s in his garage, and I met him and talked with him about the process back in those days. With the introduction of the Sony “Trinitron”, which actually still had the 3 electron guns, but had an assembly that worked slightly different as a couple of tube elements that had been 3 seperate items each in RCA, GE and others CRT’s and remained so, were now handled by one element instead of three in the Sony products. These Trinitrons were not garage rebuildable. and their introduction also corresponded to the demise of many neighbornood TV shops as sets got cheaper and repair parts got more expensive and labor became a major factor of a repair cost. Color CRT’s were rebuildable even with fused glass parts or burned phosphor coatings, but it required the facilities of on par with a factory to do so- which remained possible into the early part of this century- and they were not cheap, but it was done.

The last phase of CRT development was the elimination of lead seals, which is roughly about 1975 as the main manufacturers cut costs where they could and eliminating the lead seals went a long way towards meeting that goal. By the time CRT computer monitors came on the scene, the face glass and neck were fused to the funnel glass- no lead, and with steel pins for the gun leads, no lead based solder was needed for a connector. Just a plastic aligner was glued on the end to protect the evacuation nib and hold pins in position and provide an index so the CRT’s could be connected correctly.

So where is the lead? Simple- Lead is used as a clarifying agent for glass. The “float glass” of your home’s windows, or the tempered and laminate glass in your motor vehicles have lead in the glass as a clarifying agent as well- this is why curbside recylcling never included old windows in their segregated glass collections. The key is, the amount of lead added can only be on the order of 7% to 8% by weight- total, otherwise the glass becomes weak. So in short- when you looked at the face of the CRT, you were looking at what is known as “Lead Crystal”- just like fine Lead crystal goblets you get from companies known for the product like Swarovski. You can landfill window glass, but not CRT’s. Not even parts of CRT’s because there is so little known of their construction or evolution of the technology among those making laws or writing law administratively or involved in regulation or anything pertaining to them. They regulate something that they themselves have little understanding of- which has created a log jam that really does not need to exist.

Can the lead be recovered from the face glass? Yes, but not easily, you need a foundary hot enough to melt glass and keep it molten long enough for the lead to settle out or evaporate. Now, there have been those who profit on that lack of knowledge as it protects their industry from competition, and there is other needless wastes of tax dollars that directly arise from this lack of knowledge as well.

I base my knowledge on having worked with CRT’s in computer monitors and TV sets as well as test equipment. Plus having dismantled a few CRT’s back before the times of the excessive eroneous regulation set in. Not to mention the literature that was prodcuced in the various “Tube Data” books. Though some of those did not update after about 1967 as tubes were being quickly displaced by transistors and the need for that tube manual disappeared. That; along with an understanding of physics, chemistry, and actually evaluating many pieces of government published documents that were largely in error because they did not vet the sources of their information correctly or adequately “because they meant well” with their agenda. But those failings that have led to misinformation are not going to be addressed here with specificity, because there is not enough space. In other political climates I would show step by step what is in a CRT, but to do so here would likely have them kicking in my door for daring to open one up.

What else is in a CRT? There are the phosphor coatings in all CRT’s which can potentially be an environmental issues- namely algae bloom and potential toxicity in concentrations that “might” accumulate in uncontrolled accumulating landfill runoff. And it is important to mention that there is no Mercury in CRT’s, as it is the phosphors that light up when struck by electrons- mercury would not allow a CRT to operate in the manner they did or do, so popping the evacuation nib is the safest way to remove the vacuum. There is also Thorium on the heater filament and outer heater sleeve which is needed for electron emissions at the heart of the function of the CRT. The gun is easily snapped off at the neck and routed accordingly to recover those materials, so removing that from the waste stream is very easy and recovering those materials is fairly easy to do. However the cost of recovery of those other remaining recoverable materials is great compared to the return on the materials recovered. The color CRT’s have that iron mask, and those few remaining old vintage CRT’s (of which there are few in number these days that still have easily recoverable lead), some few of those have an iron shell- but not many when viewed as a percentage of all the CRTs that have been manufactured or are still in use. Yet recycling trade publications like a recent issue of “Resource Recycling” are still of the belief that the way a CRT was made in 1955 is exactly the same way it was made in 1995- and nothing could be further from the truth.

Therein lies the problem.

So the key is knowing how to identify the old and new technologies, but this requires those involved in regulating the recovery of the CRT’s to actually know more than they do now, or to educate themselves- but it upsets their world view- so most will have none of it.

Not all CRT’s are created equal- but all are being treated as if they are; which makes things very expensive in a needless manner. And that circles back to people “who mean well”. Those CRT’s that have a frit- are either going to have a metal funnel, or a glass funnel AND a visible parting line regardless of glass or metal funnel- sometimes it is wide enough to catch a fingernail dragged across it. Most of those will have a soldered pin base as well, not bare steel pins. While those old ones do have steel wires coming from the gun or gun assembly, those are soldered to the pin base with a lead based solder- not much, but that is one location of a small additional amount of lead and you should know you throw out more lead in a used metal squeeze tube of cyanoacrylate glue than is used at this spot. Essentially- those CRT’s with a metal funnel and a soldered pin base, will usually have lead seals, and sometimes only a Frit. Many CRT’s for test equipment were not rebuildable and were made without lead seals. I have some vintage test equipment CRT’s that are proof of that.

Most CRT’s also have a steel band around the area where a lead seal “might” be- however when you remove the band- and most of those that had that metal band that is welded will not have a parting line and will therefore not have a lead seal because the glass of the face was fused to the glass funnel. In those CRT’s the lead is only found in concentration IN the glass of the face, and these are the majority of those CRT’s still out in circulation.

To be sure, if I am the owner of a recycling company that handles a great deal of CRT’s that I can charge good money to deal with them, I would have a vested interest in promoting the idea of the lead in CRT’s as being a real environmental issue if it meant I could keep a roof over my head and put bread on my table, and maybe pocket some for profit motivation. Especially to the point of suggesting all CRT’s were made in a manner where I could point to a bucket of recovered lead (never mind how old it is- and let a reporter or article writer just assume erroneously that all CRT’s are made as they were originally right after WW2.).

The true reality is the “risk” of the glass portion of the CRT’s is really no more significant than the window glass that is allowed in the landfill (providing the neck of the CRT is removed). Now, if an alternative use of that glass and window glass can be found, such as building materials, fiberglass insulation, siding materials, concrete admixtures, etc- I am all for it. But it is largely the glass industry that should reach out and seek out the potential alternative uses for the CRT’s glass just in good faith and Public Relations because no one else is doing it. Plus right now glass is also among the least profitable of the curbside collected recyclables. Never mind that glass is highly recyclable and very sanitary. It’s main drawback is weight, plus it breaks. But personally- if I have a choice between a beverage packaged in glass bottle versus that same beverage packaged in a “PET” bottle- Glass wins because there are no hormone disrupters that could potentially leach out of the other product.

And as a side note- it was recently announced a new plastic resin is in the works that will have Furans potentially leaching into the contained products- likely to appear on store shelves about 2017. “PEF”- Polyethylene Furorate. But that drags this too far off topic, so no further mention of it in this post, other than you can research “Furans” and find quite a lot of information.

Otherwise it could take decades (unfortunately) for this CRT matter to become ancient history, and likely not be fully resolved even then. And this is largely possible when one considers the push that has led to regulations concerning manufacturers being held responsible for their products at a product’s “end of life”. (Extended Manufacturer’s Resoponsibility). I can readilly see how this could easily open the flood gates for all manner of litigations between industries that provided the raw materials or individual components of a device arising from one poorly phrased state or Federal (national) law (and few of these are ever well written or concise because many of all laws are made by lawyers intended for courts to sort out details later.). And as far as landfill runoff is concerned- there are far more toxicities of other sorts to be found than one might realize and some are in greater concentrations than what you would likely find from landfilled CRT glass.

But if nothing else- this is my knowledged “two cents” on the matter.

http://www.youtube.com/channel/UCdjcUtAAJ-CZVwaabB6SBpA

The associated blog for above youtube channel

http://altenciruits.wordpress.com/
The main blog.
the begining point place to start

https://altencircuits.wordpress.com/
The tangential blog.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine.

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Posted in Cathode Ray Tube, CRT, Frit, Homebrew, Project, Recycling, Uncategorized | Tagged , , , , , , , , , ,

Triplett 3212 “Tube Analyser”, Tube Tester

This is another out of the ordinary post, this covers the repair of a Triplett 3212 Tube Analyser. There are more than one version of this, some have the roll chart as part of the case, this one has the roll chart separate from the case. I chose to post this as I could only find some examples of the tester on the web, but nothing of the schematic. While there are some similar Triplett models with simialr schematics, the resistor values are different. I did look through “BAMA”. and those models were not close.

A tip of the coffee mug to Triplett. They are still around making test equipment and were kind enough to provide the schematic for the 3212, with fast turnaround of my request too. And again, many thanks to them.

This model has a number of examples on the web, but no schematic that is not without charge. So the schematic with a little more legible values is here, and many thanks again to Triplett for this:

3212 Schematic

Triplett 3212 Schematic

I pulled this out a few days ago to evaluate and repair the meter. It had seen a little rough handling while the glass face of the meter had been broken- Suprisingly, the only issue was a lowly spider web strand which kept the needle from moving back to the “zero” resting point, but I did not know this until I had the meter opened up to check it out. The glass piece was easy enough to replace, although I was not sure that I would have clearance with “double strength” glass initially as the original was single strength. Single strength is barely 1/16 of an inch (about 1.5mm) thick, and double strength is about 3/32 inch thick (about 3mm). The glass is held in by 6 screws and washers, and additionally made dust proof by a sealant. The sealant scraped away from the Bakelite/Phenolic face easily, but did require some care. I bedded the new piece of glass with simple gasket sealercompound, and reinstalled the mounting screws in an alternate pattern to keep pressure even on the glass and to keep it from shifting too much within the recess for the glass. For similicity of assembly, the adjusting screw was lined up so vertical, and the slot that it rides in was also lined up vertical prior to final assembly, so once assembled, when the “Zero calibration” screw was turned, the needle moved until set to correct “Zero” location.

Zero Calibration

Zero Calibration screw- only sets where the needle comes to rest for “Zero”

I did not take any action shots of the glass replacement/meter repair as this post was an after thought.

When initially tested the unit after the glass replacement, Line voltage was not able to be calibrated, it measured consisitently at 40%, so I opened the back again and checked all resistors to make sure none had opened. There is a wirewound resistor inside of the meter movement itself, but that is there so the meter itself is calibrated as a 1 Milli Ampere/100 millivolt movement (1 MilliAmp/100millivolts brings the needle to full deflection) and any deflection of the movement indicates that internal resistor is just fine when adequate current or potential is applied to the lugs.

The 2 carbon composition resistors in series that I point out in the rear view image were well out of tollerance for the circuit once I was able to compare to the Triplett provided schematic, so the pair was replaced with a metal film resistor of sufficient wattage. Other updates are the replacement of the copper oxide rectifier with a silicon rectifier (1N4007), and replacement of the old paper cap with a polyester capacitor of the same 0.1 microfarad capacitance at 630 WVDC. The copper oxide rectifier is safer than selenium, but still has significant reverse bias leakage, the silicon diode has much less leakage, so a significant upgrade to performance. This is the little black thimble sized item mounted with a #6 screw on the left side of the turret board indicated in the image- the hole is indicated, the copper oxide rectifier has been removed.

tester interior

tester interior

When I first put this tester into service after buying it at an estate sale, it would not calibrate at all, and not even respond, the original heavy duty line voltage potentiometer had corroded open, and the wirewound originally in the position where the new film resistor was installed (75k/R12) was replaced by those 2 composition resistors (pointed out as “not going to anything” in the image), and was this time replaced with the 75K film resistor, because the composition resistors were too far out of tollerance. The original R8-5K resistor was also well out of tollerance and had been replaced at that time when I first worked on it back in the 1990’s. The power cord was upgraded at that time to a grounded cord for safety reasons. The top cap wire was also replaced along with a better “Gator clip” instead of the bent wire clip.

Once it was updated for the 21st Century: this time around with “in tollerance” parts, it did not calibrate to line voltage. After reflowing many of the solder joints I could reach, I flipped it over again to test it, and no real improvement. Then I remebered that the needle on a meter face that large could be interfered with by just the static on the face of the meter. So I rubbed a dry paper towel over the face and it disipated the static charge enough to allow the needle to now pass the 40% level and be set to line level correctly. One last thing I will do is to check each of the heater/filament voltage settings to make sure they are close to what they are supposed to be. With the line level now being able to be accurately set, they should measure up quite well.

Would it have made a difference if I had deduced the static on the glass issue first? No; everything else that was done this time of repair I would be replacing anyway because the parts were out of specification or were not entirely reliable, therfore the order of their replacement/correction is irrelevent. I only make mention of it here because the issue of static on the face of these meters is not always an issue for people, but when it is- it is one of those less common things can burn a lot of time just because it is not obvious.

With a layer of mold scrubbed off it with paper towels and bleach water, it looks presentable now. I think what caught my eye originally was the large meter. And the markings are pretty much the same color they were when the meter was on the assembly line. Apart from some rust from where it had been stored between the 1950’s up to the time of that sale where I bought it, it is not in all that bad of condition.

Ready for use

Ready for use

I may have a similar knob for the #10 test switch, otherwise I may just leave it for now. The Roll charts sometimes comes loose on the ends due to the celluloid tape that was used originally, Celluloid tape will have certainly failed by now. I just used the classic translucent clear tape to re-anchor the ends, and it has worked just fine for several years since I initially put it in service in the 1990’s.

The settings for the testing of tubes are the filament/heater voltage, the circuit type, the load, and 10 switches that are set to one of three positions for the basic testing. This unit differs from the other Triplett models that may still be found. And this is an “Emission” type tester like many of the similar marked models. Some people get dismissive of them, but: 1- it tests tubes in the manner the RMA settled on, if even for a “Go-No Go” test. While it is not a perfect tester, once you get used to using it, you can tell if tubes are going to be well enough matched when in a “Push-Pull” circuit, or in balanced preamp stages such as 12AX7’s where each half of the tube is used for each stereo channel to provide acceptable results. For matching pairs or quads, a tester like the Triplett 3444 (any version) or a TV 7, or most of the EICO testers are a better choice than simple emission testers, especially if you plan on selling used tubes, or for close matching tubes via characteristics for best results.

And for 2- it has the settings for many tubes that are not even listed on other tube charts, such as the single letter tubes, and old ones such as an “00A”/”100A”, and one of the few that can test pencil tubes.

Even the best testers out there should not be used as a final arbiter of merit when used for personal reasons, because some radio chassis will still perform admirably with tubes that test low- on the order of “30” on an emission type tester- I actually have one of those quirky radios. It is one that was likely made for an electronics class as the cabinet had a rather generic look to it and no name on chassis or cabinet, or dial- but it worked very well with several tubes that would not work in other radios. I found out that it could work well with weak tubes a little by accident as I was swapping the known good tubes for weak tubes in a few other radios and just plugged the weak tubes back into that chassis so I knew which tubes went into which sockets, and one day I decided to just try it with the known weak tubes, and it worked just fine.

So if you have a tester, and you have numerous tubes that test low- test them in circuit and see how they sound. Some tubes like 6SQ7/12SQ7, 6A8, 6A7, 1A7 notoriously test low. You may have a fault developing in your tester, or you may have had a knob incorrectly set when testing (there have been a couple examples of the wrong settings being published in roll charts even) or the tubes just test low, but work fine in circuit. Let the circuit be the final judge on merit. Also double check to see that the tester is applying the correct heater/filament voltage to the tubes under test. While you may rely on the tester’s built in calibration, it never hurts to check to see if the heater’filament voltage is correct- it may be low, or in some cases, may be high if you have trouble getting repeatability in tests. More about this in relation to my own 3212 tester at the bottom.****

If you happen to be restoring an old TV set, you may find the best results with used tubes is to put the higher reading tubes (when you have several of the same type in a set) in the earlier stages. Such as if you had 5 of type 6GH8A, the tubes that tested better should go in the circuits such as 1st RF, 1st IF, Sync Amp, Quadrature, Color Killer, rather than the later stages because those first stages are critical to a good signal reception. The same is true for radios- if you have 3- 6SK7 or 6K7 for example, for best results, the highest tested tube would go into the 1st IF, or if the radio had a tuned RF stage that used that tube, it would go there. the lowest tested tube would go into 2nd or third IF. This makes the reciever more sensitive to signals than if weak tubes are in those locations.

Some last notes- sometimes a tube will test low, and sometimes this is a tube heater or filament that needs to be heated for a short while above the normal operating temperature to boil off impurities, and this can be done by increasing filament or heater voltage with no load on the tube. At the higher filament or heater setting, the meter will read higher when under test, but there are times when the general merit once the tube has cooled down; has improved to an acceptable level. It usually does not take too long, nor does it require significant increases in the heater potential. This is essentially what CRT rejuvinators did/do, and the plug in units that were sold as “Picture Tube Brighteners” usually increased the heater voltage of the kinescope (CRT) and those increased the emission of the old tube enough to be kept in service. They did work suprisingly well too.

****While trying to get the unit to calibrate for checking filament/heater votlages, it would not adjust correctly even after static neutralization, so I chose to try an alternate calibration method, and it actually worked very well. The main thing is to calibrate the tester to have correct heater/filament voltages, the other voltages will fall where they were desingned. Although replacing a Selenium or Copper Oxide Rectifier reduces in circuit resistance of rectifiction, this leads to slighly higher voltages for the “B” voltage for testing, but this is within a reasonable amount of variation, so i snot a significant concern fo emission type testers such as this one. While it may seem a cavalier approach, it really is not because the tester calibration step is supposed to establish a consistent reference point for the windings of the transformer(s) which are wound with specific numbers of turns and taps for filament voltages and test voltages of the unit. Most importantly calibrated in Emission type testers is/are the heater/filament voltages of the tubes under test.
If your alternate calibration is correct, with just the meter taking measurements, you should be able to set the switch to each position and see 25 volts at “25”, 0.75 volts at “0.75”, etc.

The steps for this alternate method is to select a tube that you have tested on other testers to know it’s relative merit. Then set this tester accordingly without installing the tube just yet. (Normally you would set the switches to the correct positions before inserting tube into test socket in normal testing as well to prevent burning out tube elements or causing other problems that could damage the tube to be tested). Only instead of a tube, you are placing meter test leads at the pins where the heater/filament would be. You need to be checking with a good AC voltmeter across the heater terminals. For my calibration test, the tube I chose to set for was a 12SK7. This tube has heater locations at- pin 2 and pin 7. So I set the number 2 switch to “up” position and switches 5 and 7 to the “Down” position as indicated in the roll chart. This is the important part, otherwise there is minimal voltage to measure at those heater/filament locations.

The calibration knob had been fully clockwise when trying to set calibration the original way, but it would not reliably set the meter needle to correct position, and was always low. However when I set up to measure the heater voltage, it was too excessive, so I adjusted the “Line” Control” down to a point where the measured heater voltage was correct for the filament voltage knob position, and that point was actually fully counter clockwise. Since I had replaced the original rheostat, there was no true “Off” position, but in that fully counter clockwise position (with the replacement potentiometer, actually being a 250 Ohm unit instead of 175 Ohms of the original); all the test voltages for the heaters, measured across pins 2 and 7 of the octal socket measured correctly. I tested my reference tubes and they were right in the range they were supposed to be, so from now on, when I calibrate this tester, I will use my alternate calibration procedure and not worry about the tester’s meter indication for calibration, but I will make sure the filament /heater voltages are correct before test. The ultimate issue may be something as obscure as the glass being double strength as opposed to single strength and thus interacting with the needle in a capacitive manner; but right now, I am not going to worry about that detail because the rest of the components of the tester checked out within specifications, and with the alternate calibration procedure the reference tubes checked out where they were supposed to, so if a tester has some issues with calibration, use the alternate method instead, as I will certainly be using the alternate method for this tester for reliability. Lastly, even though the line control potentiometer was slightly different, I had swapped that before this last calibration method because I was unsure of the condition of the initial replacement; and where it is in the circuit, (R13), it turned out to not be an issue in my case because of where it ultimately had the correct filament/heater votlages. This may sound repetitive, but I am just trying to “cover the bases” of possibilities with these testers.

http://www.youtube.com/channel/UCdjcUtAAJ-CZVwaabB6SBpA

The associated blog for above youtube channel

http://altenciruits.wordpress.com/
The main blog.
the begining point place to start

https://altencircuits.wordpress.com/
The tangential blog.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine.

Posted in Project, references, Stereo amps, Tester repair, Tube tester repair, updating tube tester | Tagged , , , , ,

Kliegl Lighting system repair notes

This post is devoid of images, but I thought I might put this up anyway in the event there are any 40 year old Kliegl lighting systems out there needing repairs. The repairs can be largely effected without sophisticated test equipment, just some patience.

I remember repairing the one system in my High School, it was new in 1970, and while not sophisticated compared to modern systems, they were a decent quality system that got away from the old “Bat Handle” controls beside the stage, but they did have a few issues that would crop up. Nothing too far out of the ordinary, but troubleshooting took time using the system itself to sort out what portion of each dimmer module was at fault. The slave dimmers were in a room off to the side of the stage, and it was really a matter of isolating the issue to either the SCR’s (common failure) or the boards mounted in the dimmers, (which were not quite as common a failure, but common enough.). The 3 sizes I worked on were the 7Kw, 5Kw and 3Kw dimmers.

The SCR’s were easy enough to test. A simple test with an ohm meter is to check to make sure the resistance was (is) high in forward and negative bias of the meter leads on the anode and cathode of the SCR. Forward Bias would have the leads oriented in the manner that the battery of the meter would flow through the device in the correct direction. If the SCR passed/passes the initial part of the testing, the Anode and Cathode will/would show a high resistance until the gate was shorted to the Anode- which would trigger the SCR into conducting mode. As long as forward bias voltage is applied, the SCR conducts without any further potential applied to the Gate lead until the voltage applied to the Anode drops to zero potential. If an AC potential is applied, the SCR acts like a diode when current is applied to the gate and when the waveform goes negative- the point where the potential as viewed on an oscilloscope crosses the zero line (Zero Crossing Point) the SCR switches off. For purposes of controlling an AC source, two SCR would be used and essentially wired oppositely to each other except common to the gate connection.

If the SCR’s check out okay, and they can also be checked by swapping the control boards between working and non working dimmer units. 3Kw and 5Kw boards are functionally interchagable for testing with moderate loads, less than 3Kw total on the dimmer, but should be kept with the original dimmer once simple testing has indicated the issue to the board or the SCR’s. the repair procedure for the board is pretty quick though it has been many years since I did that work, so I do not recall fully if there were other differences between the control boards on those 2 sizes. The 7Kw control board was a design by itself. Each dimmer slave module, regardless of size, had a large circular inductor behind the heat sinks the SCR’s are mounted to. They were potted so it was not known if they were torroidal or just circular wound. I would surmise the latter. These should not fail except in rare cases.

If the issue is localized to a board failure, the vast majority of the time the failure is with the electrolytic capacitors. In the end, on the boards I repaired it turned out that each of the failed boards had at least 2 failed capacitors, they failed “open”, so for relaibility all the electrolytic caps were replaced on each board.

However, this being the point of failure was not accepted by the classroom instructor at first until I went through and checked the transistors and other active components, which checked out fine, as they were expected to be fine by myself, having located faulty electrolytics initially. The electrolytics were all replaced on each board and when tested, the boards all worked correctly. That was my first exposure to faulty electrolytic caps as being the main cause of issue, A number of classmates were initially in concsensus with the instructor at the time because they were convinced passive components just did not fail in that manner. Well, in truth, they did, and they do. This is not to say that 40+ year old equipment may not have other failures develop on those boards in the meantime, but the first suspect in those cases of a board malfunction should always be the electrolytics first.

Shortly after the slave units were repaired and online, the 2 master dimmer controls failed> those were just a pair of transistors on heat sinks under the control panel. They plugged into the panel bulkhead with either a keyed octal or 10 pin plug, so they can be unplugged for servicing. You can get access by removing the hold down screws that are exposed around the perimeter of the control panel section- leave those in place where the hinge is though. Once the upper controls section is tipped up and secure, the master dimmer modules on that particular control board were on the right side of the panel in reference to the operator, but they can be on the left side- it is a matter of where the power to the board enters the board. The master controllers were just 2 transistors on a heat sink. Both will fail together most of the time.

While I do not have part numbers to cite, and, even if I did they can vary for many reasons. 35 Volt electrolytics were used as replacements, The originals were 25 volts, which was very close to the control voltage. The fact they failed was not a surprise. The only actual part number I can recall was the one IC I could not test with the equipment in hand- a type 301 Op Amp. I recall it only because it was the only thing I could not test. The board was populated with a few Unijunction transistors, and only one or two each of NPN or PNP type Bipolar transistors.

Modern manual lighting systems will be similar except those with central processors, or otherwise computer controlled which can differ greatly in the master control section. Most control systems today use a PWM (Pulse Width Modulated) circuit either driving MOSFETs of some flavor, SCR’s or Triac’s. Triacs are similar to SCR’s except they will conduct in both directions when “on”, they switch off when the potential reaches the “Zero Crossing Point”. The old dimmers were really little more than sophisticated single phase motor speed controllers not too terribly different in operating principles from the speed control in your cordless drill.

http://www.youtube.com/channel/UCdjcUtAAJ-CZVwaabB6SBpA

The associated blog for above youtube channel

http://altenciruits.wordpress.com/
The main blog.
the begining point place to start

https://altencircuits.wordpress.com/
The tangential blog.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine.

Posted in Auditorium equipment, Lighting control repairs, Uncategorized | Tagged , , , , , , , , ,

Reciever/Tuner tweeks short of a full alignment.

This one is a little off the beaten path, but it is something that can save you some money in some circumstances.

If a radio, a stereo reciever or tuner is not pulling in many stations on AM or FM, and you do not have alignment tools (singal generator, sweep generator, etc), AM is fairly easily adjusted, and certain portions of the FM section can be tweeked without too much effort, and without affecting stereo separation in FM. While alignment gear is needed for a full FM alignment, what I describe deals with solely those FM recievers, radios and stereo tuners that have no problems with separation or with a single station appearing in multiple spots on the dial. In that circumstance of multiple station “hits” and lack of separation, or other issues with the demultiplexer; those are issues that really require a full alignment for correct adjustment that this outline of steps will not correct. This will correct weak reception issues, and these tweeks have no effect on the demultiplexing circuitry of FM recievers.

This procedure will only marginally apply to totally digitally tuned recievers. Tweek at your own risk, but the risks are minimized if you follow the steps correctly. Plus- Mark the starting points when at all possible so in a worst case scenarion you can “undo” the tweeks if you make a mistake. Most digital tuners only have trimmers for antenna matching and some have “wave traps” which may or may not be tunable- the traps are not discussed here, but the antenna trimmer(s) may be part of the digital tuning circuit.

Note* Some digital tuners are analog tuners with a digital display. The tweeks discussed here will work on those units, but the variations in how the station numbers are displayed vary and are not discussed here beyond the simple Oscillator trimmer- this “may” or may not affect the digital display. Only a service manual will give the definitive discussion of how to correct digital displays where the oscillator trimmer does not adjust the display to the recieved station. The trimmers should not impact a full digitally synthesized tuner beyond matching the reciever to the antenna.

AM reception. First check to see if your stations line up reasonably accurately on the dial- those stations you can pull in, especially those that are weak. If your stations line up correctly, You may only need to adjust the antenna trimmer capacitor on the “tuning gang”. Some have the FM tuning gangs as part of the same gang, and some have a seperate FM gang. Sometimes, as in the circa 1969 Sansui Model 2000, there is a seperateFM tuning section, and instead of trimmer capacitors, it uses slug tuned inductance trimmers. The process is essentially the same, and in this case, the slugs in with the FM tuning section are the only slugs being tweeked. A plastic alignment tool is a must, and it must fit the slug perfectly, or else you run the risk of splitting the slug and causing other issues.

Sansui Model 2000 Tuning gangs

Sansui Model 2000 Tuning gangs and trimmer locations

The tuning gang will have sets of small blades and sets of larger blades- the AM sections are the larger blades. In the event you have a set of blades that have about the same number of blades as the larger blades, but is a little bit smaller- this smaller set is the oscillator section. adjusting that will move where the AM stations line up on the dial.

Getting back to the antenna trimmer- adjust this with the antenna attached, and on a station you can pull in weakly towards the upper end of the dial. If you have flourescent lighting noise on the power line, you may be limited to about 1200Khz or less of tunability until the antenna is matched to the reciever. If you do the adjsutments carefully, you should have no issues as these trimmers have zero impact on the stereo decocing circuits. However, once in a while you will encounter a reciever that responds a little bit slowly, or you have to rock the dial knob back and forth in order to “zero in” on the station. In that event, if it is an open gang where you can actually touch the plates, use some contact cleaner, such as LPS-1, or “Contact Cleaner” available under various manufacturer’s names- often solvent based. If you do not know if it will attack plastics or paint on the reciever or radio- check on the inside in an inconspicuous spot to be sure. The LPS-1 is non-reactive to most plastics (I have not encountered any that are attacked or fogged by it, but for everything there is first time, so just to be safe, direct the spray away from plastic parts. This would be applied at the ends where the shaft that supports the movable blades as well as the brass contacts that press against the shaft itself, or to a blade of each section to make constant electrical contact. The movable blades are at chassis potential, which is usually chassis ground.

If you have a schematic or a “map” of the component layout- often from the “alignment” section of a service manual if you can locate one, identify the AM and FM “cans” and do not adjust the FM cans- mark their starting positions jsut in case you turn one accidentally, so you can adjust them back.

IF strips

IF strips

DSC06742

Usually, the AM “cans” are going to be one oscillator coil, (adjust this only when the oscillator trimmer on the tuning gang is not adequate to correct issues of station location), sometimes you will only be able to adjust the trimmer.

There will be at least one “IF” (Intermediate Frequency”) can in the AM section, If ceramic oscillators are used, there is little adjustment you can do with these. And most of the time with older radios or recievers, there will be 2 IF cans for AM. In some cases in newer radios and recievers, one IF can may be replaced by a ceramic oscillator, and once in a great while both “IF” cans will have been replaced with ceramic resonators. These will usually be a small yellow block with “455” inked on the side or small ceramic rectangle inked on the side in most cases, and are only mentioned here if you can only find one IF, or none at all.

On some recievers, usually the expensive units, they are in a plastic case with mylar between the blades. These will have 2 or 4 trimmers on the back side of these. Typically AM or FM is going to be diagonal from each other. In these units, one is always the oscillator and you will spot it because the stations will change. Otherwise these are adjusted as above for peak signal.

I will not go into a discussion of the details of alignment of the IF”S, but I will discuss the principle of their purpose of the IF at this time, those are adjusted towards their designed peak frequency, this does a couple of things. 1) it increases the sensitivity of the reciever (sometime notably). 2) it sharpens the tuning point of a station, sometimes to the point where it is difficult to get it tuned in from the dial because it’s spot on the dial now is so small. If this happens and the tuning range from high to low is crowded to one part of the dial, you need to detune the IF slightly so you spread the tuning out over the dial. This is one area if you have an RF generator it can come in very handy, but with an average stereo reciever, they should not be that far out of tune unless someone tweeked it incorrectly previously or other circuit fault developed. Once you get used to using the radio station signals as guidepoints on the dial, the RF generator is only needed when major rebuilds are undertaken where IF’s are replaced to get them close. 3) it also deflects the tuning meter needle, which you should also view to make sure it deflects to “tuned” at the right point on the dial.

FM decoding traps/oscillators and FM IF’s should be left alone because they do require some accuracy in the alignment, and while the IF’s determine where things line up and how many times on the dial a station occurs, they require a great deal of patience and luck if you try to tune these with the tuning meter- in general, these should not be touched, although sometimes you can improve reception by tweeking the first IF only slightly. This may seem contradictory, but it is not. If you have a very good ear, and pay attention to the tuning needle and scrupulously check tuning linearity across the dial, this would be an adjustment of last resort. Not for the faint of heart. If you get the first IF too far out of peak tune, a full alignment is what you have to do, and that is not the scope of this post.

However with all the caveats and cautions, under normal circumstances, you should not need to make much of an adjustment, usually less than a small fraction of turn to get the first IF stage peaked.

In the end what your goal is: 1) To tweek the trimmers to achieve maximum sensitivity by matching the reciever to the antenna you have in use. As the first step and as you make other adjustments, you want to peak the signal. 2) Have linearity of tuning across the dial face. 3) Have the stations line up where they are supposed to on the dial.

The first few times may be agravating. There are times when only slight tweeks need to be made, and once you get used to making the adjustments, if you do it correctly, you can tune up the AM section very quickly.

On less expensive radios, they have a small plastic case which contains the tuning gangs, On these- mark your starting points, and once you have identified which two are for the AM/MW section- mark them in some way so you do not disturb them when you move to the FM section. In most cases, one will be directly acting on the oscillator circuit, the antenna trimmer will be diagonal to it. If there is also a Short Wave and/or a Longwave band, these will their trimmers near the tuning gangs as well, but will usually be on the chassis. These tweek the same was as the AM/MW trimmers- if you peaked the IF’s on AM and have everything correct, the IF’s are left alone at this point because the Long Wave and Short Wave bands use the same IF’s as MM/AM.

FM Section:
This is largely the same basic steps as the AM section. The Multiplex section rarely changes and as long as it is not disturbed, the need for a sweep generator is minimized. I transplanted a Demultiplexer removed from an inexpensive solid state console reciever into a Heathkit FM Stereo tuner that dated from about 1964. The unit had a broken coil I could not locate a replacement for. It had easily adjustable separation on the front of the unit originally to accomodate other decoding schemes if a different decoding method had been chosen by the FCC.

The primary adjustments on a typical Stereo reciever are going to be simply the antenna trimmer, the oscillator trimmer and the first IF can only (and rarely). Once in a while, if the reciever has trouble tuning in stations when it is in “FM Mute” mode, you will find the antenna coil roughly even with the section of the tuning gang corresponding to the antenna trimmer. You can really only tweek these with a very high accuracy by paying attention to linearity across the dial, narrowness/accuracy of tuning- using the tuning indicator to know when on a station as well as relative signal strength. There is also a threshold adjustment on the muting circuit, but often tweeking the antenna trimmer is all that is needed to get correct operation back.

On some tuning gangs there are three sets of FM tuning gang sets, with the one furthest from the “front” of the tuning gang being the oscillator (usually, but not always, Sansui has the oscilaltor next to the tuning wheel of the tuning gang.). In some cases, you will have two trimmer caps for the FM section. In this event of 2 trimmer caps on a 3 gang tuning section, the furthest one will directly interact with the position a station will tune in on the dial. If not, there will be an FM Oscillator coil with a tuning slug, So you can locate the station first, if the frequency is known- verify where it is in relation to where it needs to be. If the ocscillator close does not get you close enough, after the antenna trimmer, or coil has been peaked, you need to adjust the oscillator coil as the end step until things do line up, and the antenna trimmer should be adjusted for peak signal as well as the accuracy of the station locations because it also affects the sensitivity of the unit to some degree. The antenna coil will be right in the vicinity of the oscillator section of the tuning gang.

On those with PLL IC’s, there will be a small variable resistor that adjusts threshold of the “Stereo” indicator. Once the antenna has been matched to the reciever, this adjustment can be tweeked on a distant station that you should be able to recieve a stereo signal from- usually 40 to 50 miles is a good benchmark. It should only be adjusted if the antenna trimmer has not improved a PLL “Lock” on those stations, and it should only be adjusted to a point where it does just lock on those distant stations.

When tuning, it is best use a non-magnetic screw driver, but if you have no choice- you end up spending a bit more time to “dial in” because the magnetic screw driver will interact with the tuning components, and one needs patience if using one.

Also-if tweeking any tuning slug- you must match the slug drive exactly or you will split the core. Nylon tools are best and reduce the chance of splitting a core.

http://www.youtube.com/channel/UCdjcUtAAJ-CZVwaabB6SBpA

The associated blog for above youtube channel

http://altenciruits.wordpress.com/
The main blog.
the begining point place to start

https://altencircuits.wordpress.com/
The tangential blog.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine.

Posted in Amplifier repairs, recievers and tuners and guitar amps | Tagged , , , , ,

Just Some Idle Notes

Once again I will look at refining one of the pulse charger designs. This is just theory for now, I hope to have a working circuit up reasonably soon.

Essentially the goal is to make the pulse charger in a way that cycles off for a period of time and then back on, in a continuous manner. This will hopefully overcome the issues of diffusion (lack of it within the cell as it is charging) and gas liberation which usually causes the failures of the cells which manifests itself as leaking, excess heating or breached seals.

Even though the initial “Reverse Current” Charger dates back to the later 1950’s, the batteries made back then were predominantly of the “Carbon/Zinc” manufacture, which is still around today however the outer Zinc jacket is made so thin, there are holes in the Zinc by the time you purchase them. Ir was this type the orginal charger was made for. The fact it works very well for Nickel Cadmium and Nickel Metal Hydride cells as well as Lead Acid cells keeps it a timely circuit.

Alkaline cells, Mercury cells (few available), Lithium Ion and Silver/oxide cells do not take the reverse pulse well at all. The Alkaline cells being the focus of the pending charger is the goal. The Alkaline charger that is discussed here and in the other blog does work to a limited extent. The modification will be the addition of a main timer circuit to essentially shut the charger off in a cyclic manner to allow for normal difusion of material within the cell to occur.

Other chargers have been attempted for charging “Primary” Alkaline cells, but they too suffered various limitations, from undercharging the cell so it had minimal capacity, or they suffered from the same failures from heat of the “Alkaline Charger”- Namely leakage and small explosions. This is usually the result of a lack of diffusion and localized heating within the cells. The cycling will hopefully address this issue so effective charging will occur.

At the moment, with this just a theoretical excercise I do not have a circuit to add at the moment, but I will try get something up soon. I have a massive reconstruction project which will launch it’s own blog and videos so I cannot guarantee timelines.

http://altenciruits.wordpress.com/
The main blog.

https://altencircuits.wordpress.com/
The tangential blog.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine.

Posted in Alkaline Charging, Alternative Energy, Battery charger, Bedini, Capacitive charger, Capacitor charger, charger, Homebrew, Incandescent light bulbs, lead acid batteries, Project, Renassaince, Reverse Current charger | Tagged , , , , ,

There will be more to come…

I am just busy with a home renovation, which is moving slower than expected, but there are several posts in the works, just not completed yet

Posted in Alternative Energy, Alternative Energy System, Project, Uncategorized

The links for the relevent alternative energy blogs

http://altenciruits.wordpress.com/
The main blog.

Yes, I know that I misspelled part of it, but I caught it in time.

https://altencircuits.wordpress.com/
The tangential blog. You are here.

http://passivesolarproject.wordpress.com/
The passive solar blog- outgrowth from some projects of mine. There will be some developments in this bolg area coming up.

Posted in Alternative Energy, Alternative Energy System | Tagged