Buying, Restoring and Calibrating the Eico 666/667 Tube Tester by Mike at MDBVentures.com 22 Feb 2008 (Updated 31 Dec 2023) http://www.MDBVentures.com - Great prices on great tubes! The Eico 666 and 667 Tube Testers are both one of the best and the worst tube testers ever made. The design of the tester itself is very good and even has advantages over the Hickok testers. The Eico's do a better job of testing emission and leakage. For most tubes, the Eico's also do an adequate job of testing the gain of the tube. Given the price of a good functional Hickok tester these days, an Eico can be a good low cost alternative for those on a budget. To test Compactron tubes, you will need an Eico 667 or else get a model 610 adapter for the 666 tester. The down side of the Eico Tube testers is that the tube charts for them are loaded with errors. If you are not careful and cross check the settings with a tube manual, you can easily destroy the tube. The Eico testers were sold both in kit form and as factory wired. For obvious reasons, the kit built testers tend to have more problems than the factory wired testers. However even factory wired testers can have problems. How to tell if an Eico tester was factory wired (other than having professional looking solder job inside). The factory wired testers will have a "W" tag on the serial number. Kit built testers do not have the "W" tag. You may also see an ink stamp "Tested" with the initials of the person who checked the tester along with the date stamped on the bottom of the roll chart assembly, although this can also appear on kit built testers that were returned to the factory to be repaired when the kit builder couldn't get it to work. Although if the roll chart assembly came from an organ donor tester, it may not reflect tester's original build source. Nor does it appear that the stamp was always done. I've seen factory built testers without the stamp on the roll assembly. The difference between the 666 tester and the 667 tester is that the 667 replaced the old preoctal sockets with Compactron and Nuvistor sockets so that the newer tubes can be tested. Also the fuse was moved from inside to a panel mount to make it more easily accessable. The only other real difference was they changed the knobs on the selector switches from round knobs to paddle knobs. Myself, I prefer the round knobs, but that is just me. Inside the testers, the electronics is the same, so the same test charts will work for both tester models. With the exception of the additional tubes the 667 tests, which require the 610 adapter to test on the 666 and thus a separate chart for those tube tests. (The last test charts for the 666 provide the setting needed for use with the 610 adapter.) While the 666 and 667 testers are good testers, they do have a couple of design issues that could have been "fixed". The most serious is that if there is a grid short to cathode, screen or plate in the tube, it can burn out the grid bias control when you pull the merit lever. Both the grid bias and the plate load control are not available anymore (Eico closed it's doors in 1999). The only way to get direct replacements is to cannibalize another 666 or 667 for the parts. Note: It is possible to use a different control that has the same characteristics which you might find from electronics suppliers such as Digikey, but keep in mind that the control end point positioning may be slightly different, so they may not be as accurate as the original controls for which the panel was marked. Of course having a working tester even if it is not as accurate is better than no tester at all because of a burned out control. We do have a few replacement parts available, including the Grid and Plate control pots noted in the article below. To see the parts we have available, go to http://www.fourwater.com/equip/eico666-667-parts.txt Replacement grid and plate controls: There is a CTS control that appears to be an acceptable replacement for the grid control (5K 5W wirewound pot with switch) CTS part number 026TB32R502B1B1 The part is available from Digikey or Mouser. I've used the part in a restoration and it appears to work ok, although you may want to cut the shaft down a bit so that the knob is closer to the front panel. The shaft is 5/8 inch long, but the Eico is expecting a 3/8 inch long shaft. Since the shaft is made of aluminium, it is easy to cut with a hacksaw. I have yet to find a plate control that is an acceptable correct replacement, although I have found a few 3.3K pots that can be made to work with only minor measurement error. See the file eico666-667-repair.txt for more details on repairing the grid and plate controls. Modifications: Grid Control Protection: Given the difficulty of finding replacement controls, I have added a modification to my 666 and 667 testers to protect the grid bias control. The plate load control is not as much a problem, I've never seen one burned out. The meter would be damaged long before the plate control would be damaged. The meter is in series with the plate control and the plate control can handle much more current than the meter can. If the meter is gone, then you have a much bigger problem than a damaged plate control. Of course it is possible to damage the plate control by accidently shorting it to the chassis while poking around inside the tester, but hopefully you will not have power applied to the tester while it is out of it's case. Also, you do not want to put anything in series with the plate control since it is an important part of the plate current measurement circuit, so any changes would affect the accuracy of the emissions measurement. That doesn't mean the plate control is trouble free. It has a problem of oxidation on the internal wires and rotor assembly if it has been left sittn gofr a long time. Most units that have been sitting unused for years will likely need to have the plat control cleaned, which luckily is easy to do on the 666 and early 667 testers. The grid bias control protection modification is very simple and easy to do. It uses a trick borrowed from the late model Hickok testers. A lamp is placed in series between the grid control and the tube. This is done by unsoldering the wire to the center connection of the Grid control and soldering one leg of a minature bayonet lamp socket to the center connection of the grid control. The wire you disconnected from the grid control then goes to the other leg of the lamp socket. When done, insert a type 47 lamp (6.3V at 0.15A) in the socket. Actually just about any 6.3V lamp will work. I picked the #47 because that is the lamp that is used as the pilot lamp for the Eico testers (so in a pinch the pilot lamp can be used). The 0.15A is enough to protect the grid control while not inserting too much resistance in series with the grid (5 ohms cold resistance). A type 44 lamp would work as well (0.25A 3 ohms cold resistance). If you are concerned about the current, you could use a type 49 lamp which is rated 2 Volts at 0.06A and has a cold resistance of 4 ohms. (The Hickok testers use the type 49 lamp.) The cold resistance is what is really important, while still having a higher on (hot) resistance. There is an advantage to the 49 lamp as it has a higher on resistance which can provide better protection, but if you are testing a tube that has a high grid current, the higher on resistance may affect the grid voltage and thus the test measurement. Note: Make sure that the lamp socket is well mounted so that it doesn't move around and short out to anything. Keep in mind that on some bayonet sockets the lamp base Connection is tied to the mount bracket which will tie it to the chassis ground if you attach it to the chassis. Try to use a socket that has an isolated mount. The lamp connections must not be connected to ground, so make sure that it doesn't touch the chassis as that can cause the grid control to burn up (which is what we are trying to prevent with this modification). Note: You must use an incadescent lamp for this modification. Do *NOT* use an LED lamp. They will alter the circuit operation and not provide the proper grid voltage to the tube being tested. Note: I have had the lamp burn out when I pulled the merit level while testing a tube that happened to have a shorted grid. (Which is why you are always supposed to test for shorts first...yeah, sure, we all do that.) The result is not specifically identifiable as a problem unless you happen to know what to look for. In my case, all the tubes were showing 20% emission, even known good tubes, because the grid no longer was being supplied with a bias voltage. Instead with the lamp burned out, it was floating, so the tube was acting as a simple rectifier. You can quickly test the grid control voltage by setting the grid control to 100, lever switch 1 to position 1, and lever switch 2 to position 5. Set all the others to 1. Set the V and S levers to position 1. Make sure the Trasnsitor switch is set to Tube. The plate and filament control positions don't matter for this test. Press the Line Adj button and make sure the meter is centered on the Line adjust mark. Press the number 2 push button to latch it. Place an AC meter leads in pins 1 and 2 of any of the tube sockets. Pull the meit lever, you should see around 6 Volts AC. If you see something lower (such as 2 volts), the lamp is probably burned out. Meter protection: A pair of back to back (in parallel) 1N4148 diodes across the meter can help reduce meter damage by limiting the current drive into the meter when the voltage is excessive. Connect the cathode of diode #1 and the anode of Diode #2 to the meter + terminal. Connect the anode of diode #1 and the cathode of diode #2 to the meter - terminal. Alternately if you don't want to pull the meter out to get access to the terminals, you can place the diodes on the transistor switch. Just follow the meter leads to where they attach to the switch. Or install a terminal strip, install the diodes on that and connect wires from the diodes to the switch instead. A common problem is a bent meter needle caused by a shorted tube or incorrect test setup for the tube. This can cause the meter needle to slam into the right stop bending the needle. In extreme cases it can even burn out the meter. The diodes help to limit the current into the meter by limiting the applied voltage to less than 0.6volts. The normal maximum voltage across the meter is 0.2volts rms (0.288 volts peak), well below the 0.4 volt point where the 1N4148 diodes begin to conduct. Since the 1N4148 diodes don't turn on until about 0.4volts or so, they have no effect on the normal operation of the meter. The 1N4148 diodes can handle up to 200mA normally and up to 1 amp for a short duration (1 second). This is more than adequate for the meter circuit (200uA maximum). The 1N4148 is preferred over larger diodes like the 1N4004 because the 1N4004 has a higher turn-on threshold and higher leakage than the 1N4148 diode. So the 1N4004 type diode is not as good of a protection diode for the meter circuit. I've also seen some people put a 1uf to 10uf 6volt capacitor across the meter to slow down the current surge and thus how quickly the needle moves. I generally don't do that because electrolytic capacitors can get leaky over time resulting in incorrect meter readings. There is also the issue that the Eico circuit is actually using pulsed DC (half waveforms of the AC that is being rectified by the tube under test). Putting a capacitor on the meter will store the charge resulting in higher readings than there should be. So I really don't recommend it. Another potentially useful part to add would be a 0.01uF ceramic capacitor (X7R or C0G, 16V or higher) across the meter. This won't help much to control the current surge, but it will help to reduce parasitic RF oscillations or external RF from affecting the meter reading. However, it can also change the meter readings because it acts as a storage device which will supply more power to the meter than would occur without the capacitor. Also since the diodes and capacitor can act like a detector in a strong RF field, it can actually make the problem worse in certain situations (like operating next to a transmitter tower). Usually this is not a problem, but is something to be aware of. As with the 10uF capacitor, I have not found the 0.01uF capacitor to really be much help. In the end, I don't recommend putting a capacitor across the meter as it usually just generates more problems than it fixes. If you do have problems of a know good tube not testing they way it should, read this file: http://www.fourwater.com/files/eico666parasitics.txt There are a couple of other capacitors that can be added to help reduce problems with parasitic oscillation. These are optional, but it won't hurt anything to add them. One of the capacitors (0.01uF 400V) should go between the control grid connection to the bias protection lamp fuse that you installed (you did install it didn't you?) and ground. If you did not install the lamp fuse, then the capacitor can be connected from the center position of the grid bias potentiometer to ground (chassis). This connection should be fairly short. I usually add a star lug to the screw that holds the selenium rectifier in place and connect the capacitor to the lug. (Note on the later 667 testers the selenium recitifer location was replaced with a terminal strip and wires run to a new location for the selenium rectifier which is on the transformer mount (where the fuse was mounted on the 666 tester). On some of the 667s (last builds) the selenium rectifier was replaced with a silicon diode directly tied between the filament switch and the terminal strip. The other optional capacitor (also 0.01uf 400V) to add should go from the meter negative terminal to the chassis ground. This is harder to install as there is no easy place to connect the capacitor to ground from the meter and doing so would make servicing the meter much more difficult. The alternative is to connect it to the switch where the meter wire connects, but that creates the potental of damaging the switch unless you are very careful. Because of the risk of damage and minimal potential for improvement (same issues as the capacitor being placed across the meter), I generally don't add the capacitors. If you install these capacitors, they should be ceramic capacitors. The purpose of the capacitors is to reduce the potential for parasitic oscillation, so a low inductance capacitor (ie ceramic) is the best choice for that work. One thing you could do though if you have the meter out in order to add the protection diodes is to add a ferrite bead to each of the meter leads. The easiest way to do this is to find an old TV balun core. Remove the wires from the old core and feed the meter leads through the core. Then connect them up to the meter. That won't stop all potential oscillations, but it is very easy to do and will reduce any potential problems with RF oscillations. If you don't have a balun core available, just about any small ferrite that you can thread the meter wires through will work. However, like the capacitors, this is of little or no real world help, so in the end I don't add the ferrites either. For a schematic diagram of the mods see the file 666-667-mod.png Note: There is a potential issue with installing the protection diodes. If parasitic oscillation is occuring in the tester, the diodes can potentially make it worse. Although at that point you aleady have a problem that is disrupting the test results, and the diodes still are protecting the meter. For more information about parasitic oscillation problems in tube testers, see http://www.fourwater.com/files/eico666parasitics.txt Buying the testers: When looking for a 666 or 667 tester to buy, there are a few things to watch out for. The most important is that the meter should work. Power up the tester, and press the "Line" button. Moving the "Line Adjust" control should cause the meter needle to move around the center position on the meter. Also make sure that the needle is not bent and doesn't stick. Note: If the meter cannot be centered, this can sometimes be fixed (see the section under restoration), but the tester will not work properly if the meter can not be properly centered. Also if the meter doesn't move at all, it is likely that the meter is broken and the tester will only be good for parts. Although it could also just be that the tester is just very dirty inside or incorrectly wired. The only way to know is to dig into the circuits inside, which a seller is not likely to let you do that. The next important thing is that there are 14 screws around the edge of the tester that hold it in the case. Make sure that all the screws are present. One or two screws missing isn't a serious problem, it may mean that they were stripped by someone who over-tightened the screws. The reason for checking the screws is that if there are no screws, or only a couple of screws, it is likely that there is something wrong with the tester, and the last person who worked on it didn't consider it worth even bothering to put all the screws back in (they might have kept it as a parts unit). Also check for rust on the screws. Light rust is not a serious problem, most old testers will collect some rust. But, heavy rusting is an indication that the tester was stored in a damp area and may have corrosion internally. For the same reason, carefully check any tester that has new screws, as it indicates that the original screws were not in the tester or were rusted at some point so someone put new screws in possibly to hide the problem. It may just be that someone did a restoration on the tester, so don't worry about it too much if the tester seems to look ok otherwise. The ability to adjust the meter with the line adjust control is probably the single most important test for the tester. Check that all the knobs are present. Missing knobs is an indication that the tester may be was a parts unit. Although they may have just gotten lost. The knob on the merit switch does have a tendancy to pop off or even crack on a tester that has seen some use. Also check that the two plastic covers over the roll guide are intact. It is normal for these to be yellowed with age, especially if the tester was exposed to sunlight for any length of time. If these windows are missing, it is an indication that the tester may have been used as a parts source for another tester. Again, don't worry too much about the missing windows, they may simply have gotten lost. The tester will still work fine if that is the only problem. The roll chart should be present, if it is not, this is another indication that the tester may have been used for parts. The roll chart should not bind when you turn the knobs. There may be some "tightness" and a bumpy feeling as you move the chart. That is not a problem. They used a rather stiff spring and things tend to bind a bit if it hasn't been used in a long time. There should not be any rips or tears in the chart. You don't actually need the internal chart, as you can use a chart book instead. Myself, I normally just use a chart book (so that I can "fix" the chart errors as I discover them). A missing or damaged roll chart does not itself prevent the tester from working, but a missing roll chart is an indication that the tester was used for parts so there is likely to be other problems with the tester. Check that the meter face is not cracked. This is a common problem, while it does not prevent the meter from working, it can be a distraction, and an indicator of potential trouble with the tester. It is normal for there to be some minor surface scratches and/or scuffing on the meter face if the tester has been used. Use anti-static eyeglass or camera lens cleaner to clean the meter face. Don't just wipe the meter with your hand or a dry cloth as it will pick up a static charge that will affect the meter reading. Do not use a wax based spray on the meter as that will encourage static build-up. Warning! Do not over spray the meter. A small dab is all that is needed. More is not better. (See the Calibration section below.) Make sure that the cap connector is intact. The Bakalite insulator on these sometimes breaks. It does not prevent the tester from working, but does make it more dangerous and more difficult to use the tester. Also, the attaching wire should be flexible and without cracks or missing insulation. This is not serious if you are intending to restore the tester. You can replace the wire with Beldon #8899-100 black 18AWG 5000Volt test prod wire (or equivalent). If you can't find the test prod wire, you can use a lamp power (or speaker) zip cord and strip it down the middle. Cut off a 15 to 16 inch (about 40cm for you metric folks) length of wire and use that for the connector wire. The power cord should be intact and flexible without any cracks or missing insulation. If the power cord is stiff or cracked, it can easily be replaced with a lamp power cord or a two wire extention cord with the socket end cut off. So this is not a serious problem, but it does mean that you will have to fix it. A stiff or cracked power cord means that it was not stored well and so may have other internal problems. Although keep in mind that these testers are 50 to 60 years old, so there is going to be some stiffness in the power cord even if it was perfectly stored. If you can, check that the tube sockets are all clean and that the tubes fit in them tightly. The Octal socket, 9 pin minature and 7 pin miniature sockets are the most important ones to check as they are the ones that get used the most. For the 667 tester, also check the 9 pin Novar socket. This socket gets used for two different tube types that have different pin sizes. Forcing the large sized pin tubes into the socket will distort the socket so that the more common thin pin tubes won't be properly seated in the socket. You may have to replace the socket (or live with holding the tube off-center to make a good connection while testing it). On the 666 tester, also check the preoctal sockets (four large sockets top left corner). This assumes you will be using the tester to test old preoctal tubes. (Presumably this is why you bought it instead of the 667 tester.) They should all be tight. Keep in mind that the four pin socket is going to feel looser than the seven pin socket because there are fewer pins for the socket to grab on to. The sockets are a pain to replace, so it is desirable to get a tester that doesn't need them replaced. Restoring the tester: Note: This is just a quick overview of what to look for and expect when looking at the tester before buying it, how to calibrate it and the most common repairs needed. For a more detailed restoration/repair article, see the file eico666-667-repair.txt. As long as the tester is in otherwise good condition, there is very little work that needs to be done to an Eico 666 or 667 tester. Use mild soap and water to clean the front panel. For tougher grime, use isopropyl alcohol (ie rubbing alcohol). Note: be sparing with the soap and water or alcohol. You don't want to have it dripping all over on the circuits inside the tester. For the meter face, use eyeglass or camera lens cleaner or computer monitor anti-static cleaner. You want to use something that is non-abrasive, non-corrosive, does not leave a film, and is anti-static. Since the meter cover is made of plastic, it will easily pick up a static charge even just by touching the meter face. This can cause the meter to read incorrectly. If the meter was working but then stopped returning to zero, try using the anti-static cleaner on the meter. If the needle drops back to zero, it was being affected by a static charge on the meter cover. Warning! Do not over spray the meter face. Only a small dab is needed. Excessive spray can seep inside the meter via the mechanical adjustment and potentially cause problems. (See the Calibration section below.) If you have a meter with a scuffed face, it may be tempting to use a wax compound to try to restore the meter face...DON'T. The wax coating will cause the meter face to collect static electricity which will disrupt the operation of the meter. It is very sensitive to static. It doesn't hurt the meter, but it prevents the meter needle from operating properly and can result in an inability to adjust the meter properly, or to significatly disrupt the meter reading. You can use a good contact cleaner to clean the switches inside the tester. Do not use one that leaves a residue behind as that can interfer with the operation of the switches. This is espacially true of the push button switches which are overly sensitive to this problem. (See the file eico666-667-repair.txt for more detail.) I used to recommend Deoxit, but I have found that it tends to cause the switches to go bad again rather quickly because it leaves a residue behind that collects grime. WD-40 contact cleaner (the contact cleaner, NOT the lubricant!) or CRC contact cleaner should be a good alternative. Be careful that you don't accidently spray the paper roll chart. Holding a piece of paper or cardboard in front of the chart can help prevent that problem. Or better yet, just remove the paper roll assembly. This can be done by removing the four screws next to the paper roll advance knobs (two screws next to each knob). Also be careful of not spraying too liberally or you will end up with a dripping mess all over the place. I would suggest putting a piece of cardboard beneath the tester first to catch the overflow. Fixing sticky buttons: If the tester has sticky buttons that won't won't stay down or won't release when you push the Reset button, that is usually caused by the button rubbing against the hole it goes through. The first thought is to loosen the screws that hold the switch assembly to it's mount plate to move it. That won't work. The holes are precision and do not provide enough slop to adjust the assembly that way. Nor is it a good idea to try to blend the mount plate to try to fix it. The fix is actually rather simple once you know the trick. Remove the knobs from the Filament, Line Adjust, Grid and plate controls. (Use a small flat blade screw driver to loosen the screw inside the flat end of the knob.) Now loosen the nuts on all four controls that hold the controls to the front panel (don't remove them all the way). You can now move the push button assembly mount plate to center the knobs in the holes. Once the buttons move freely, tighted the control nuts. If the buttons still stick, loosen the control mount nuts and try again. The switch assembly may have moved when you retightened the control mount nuts. When done, be sure to put the knobs back on correctly. See "Calibrating The Tester" below for instructions on correct placement of the Grid and Plate control knobs. The set screws in the Filament and Line Adjust knobs go against the flat area on the control shaft. Fixing the plate control: The plate control can sometimes develope contact oxidation and/or contamination on the resistor coils inside. Especially if the tester has been sitting unsused for many years, which is what the likely situation will be with most of the testers ecountered these days. If you have problems with calibration trimmers, you are likely going to see this problem with the plate control. Luckily it is usually easy to fix. On the 666 you can pop off the back cover with a screwdriver and spray it with contact cleaner. Move the control around a few times to help clean the contacts. Don't forget to spray the rotor contact in the middle of the control as well. If the resistor coil contact has problems, then the center rotor contact will also likely have problems. (See the file eico666-667-repair.txt for more detail.) Warning: Don't scrub the control very hard or you will damage the wires. Just lightly rub the Qtip over the wires. After you are done and it has dried out, just snap the cover back on the control. Note: On later model 667 testers the back cover doesn't come off. The best you can do if it has this problem is try to find a hole to spray the contact cleaner through, or just move the control back and forth a lot and hope that clears the problem. If it doesn't, you may have to replace the control, which can be a problem since they don't make 3K ohm wirewound controls these days except by special order. (Do NOT substitute a different value or the calibration will be all wrong.) Fixing the grid control: The grid control is more of a problem because of the switch. But, on older 666 testers you can pop the back cover off of it too. First move the control to the center position (around 50 or so). Then pop off the back cover with a screwdriver. Be careful not to damage the locating tab located above the center connection of the control. Spray the control with contact cleaner and move the control to work it in. Once the control has dried out, make sure the control is positioned in the center (around 50) and carefully put the cover back on. The locating tab will fit through the hole in the back cover (be careful not to damage it). Unfortunately on newer 666 and 667 testers the back is not easily removable without damaging the control. However CTS does make a control that seems to work as a grid control replacement. CTS number 026TB32R502B1B1 - 5K linear wirewound 5Watt with SPST switch. (See the file eico666-667-repair.txt for more detail.) Be very careful not to spray the two calibration controls, R7 and R18. These controls cannot be cleaned with contact cleaner, and trying to do so may make them leaky. If you need to clean these controls, follow the steps below, or just replace them with sealed controls instead (recommended). Fixing the calibration controls: The R7 and R18 controls are snap in potentiometers mounted on plates. One (R7) is near the filament switch, and the other (R18) is near the line calibration control. These controls are not sealed, so over time they tend to collect dirt and grime. As a result, they become "leaky". This is the single biggest cause of calibration failure in the 666 and 667 testers. Luckily it is easy to fix. You can either replace the controls with new ones (100K ohm 1/2 watt linear trim pot), or you can clean the existing pots. If you decide to replace the trimmer pots, use sealed ones so that they don't collect dirt like the original parts do. Note: If you can't find the 100K sealed pots, a 150K or even 200K pot will work. The exact value is not critical as they are simply used a a variable resistor, although do not use a value less than 100K as it will prevent you from being able to do the calibration. The normal position of the 100K pot is approximately centered at 50K of resistance. To clean the existing pot, you will need to first remove it. To remove the pot, first carefully mark down the connections to the trimmer pot, then unsolder and remove the connections. It is sometimes possible to remove the pot with the connections intact, but I don't recommend it for a novice as it is a good way to do some serious damage. Use a pair of needle nose pliers or a screw driver to gently compress the two snaps on the control shaft and push the control out of the mount plate. There are four bent tabs that hold the back shell on the pot. Unbend these tabs enough to remove the back shell. I use a pocket knife to pry them loose, then a pair of needle nose pliers to open them up. The shaft and front snap-in plate will also come out at the same time since the back shell holds it all in place. Now that the resistor surface of the potentiometer is exposed, take a soft cotton rag (such as an old tee-shirt) and soak a portion of the rag in isopropal alchohol. Now carfully wipe the surface and surrounding area of the resistor area of the control. *DO NOT* scrub it. If you scrub it, you will damage the resistor. Just very lightly wipe it clean. Once you have cleaned the control, put it back together. Place the shaft back in with the stop "ridge" on the back of the control shaft 180 degrees away from the middle connection of the pot. Place the snap-in plate over the shaft on the front. Now place the back shell on the back of the pot. Bend the tabs back down with a pair of pliers. Make sure that the cut out on the backshell is over the pot connections, or you will short them out. (Yes, I've done that a couple of times.) Luckily it doesn't hurt the tester other than it won't work until you fix the mistake. Reinstall the pot back in the tester. (Hopefully you remembered to note down how it was connected.) Once you are done cleaning (or replacing) the calibration pots, you will have to recalibrate the tester (see the calibration section below). Note: I have found that once the calibration pots go bad, they quickly go bad again, which is why I recommend replacing them with sealed controls. Other components to check/fix: There is a 10mfd 150V electrolytic capacitor located near the filament switch. This is connected between the chassis ground [positive] and the leak test/meter calibration rectifier [negative] (which is also connected to a 270K resistor). There is also a 10mfd 25volt electrolytic capacitor located on the transistor test switch (this is only used when testing transistors). It is usually good to replace electrolytics in old equipment when doing a restoration. The electrolytics dry out and can get leaky over time and don't work as well (if at all). However the capacitor on the transitor test switch can be difficult to replace. It seldom actually goes bad, so you may want to just leave it alone. It should be noted that there is a 680 ohm resistor in parallel with the capacitor which will interfer with testing it in the circuit. If you want to check it with a capacitance meter, you may have to clip one of the leads to remove it from the circuit and then solder it back if it checks ok. For more information on repairing the transistor test circuits, see the file "eico666-667-repair.txt". The precision carbon film resistors will usually not have any problems. There are four carbon composition resistors as well (round brown resistors). These can sometimes go bad as they tend to sometimes increase in resistance over time, so always check to make sure they are still within tolerance. The two wire wound resistors are usually trouble free. There are two diodes in the tester, one selenium rectifier for the tube circuits (may be a silicon diode in late model 667 testers), and a germanium diode for the transistor test circuit. I've seldom seen these go bad other than by fumble fingered technicians or kit builders destroying them accidently. If you do need to replace them, the germanium diode can be replaced with pretty much any other good quality germanium diode such as a 1N151. The selenium rectifier can be replaced with a silicon rectifier such as a 1N4004. However, there is no need to replace the dioes (and I do not recommend it) unless there is a problem with the original parts. Note: I've seen references that the selenium rectifiers are bad. In most cases, the "bad" selenium rectifier is prefectly fine, the problem is simply not knowing how to test the rectifier. Selenium rectifiers have a higher turn on voltage than silicon diodes so the normal method of checking them with a ohm meter will show them as being open when they are perfectly fine. The best way to test the selenium rectifier is while it is in the circuit to see if it is producing the proper DC voltage. You can check if the rectifiers are bad by looking at the DC voltage at the output. With the Line Adjust set to the calibration point, the germanium diode should have +5 Volts DC +-2V at the cathode end (positive terminal of the 10uf capacitor) relative to the chasis ground. The selenium rectifier should show -65 Volts DC +-10V relative to the chassis ground. However keep in mind that an open filter capacitor will cause the voltage to show lower. That is a problem with the capacitor, not the diode. Note: See the eico666-667-repair.txt file for additional information on this. Note: The germanium diode used in the transistor circuit can be replaced with a silicon diode (such as the 1N4148), however it may affect the transistor test results as the silicon diodes will have a lower voltage drop, however this is a minimal effect (power = 4.8V vs. 5.3V DC), so if you don't have a germanium diode, you can use the silicon diode instead. However, there is normally no need to replace it unless it has been damaged. In addition, a design note here, the 680 ohm resistor causes the charge on the 10uF capacitor to bleed off faster (1tc=6.8mS) than the 60Hz charge rate (t=16.7mS) and since the capacitor is only charged on 1/2 wave cycle, the charge time is restricted to the peak portion of 1/2 wave at 60Hz. What this means is that there is a 2.5V AC ripple riding on the 5 Volt DC power. I'm not sure why they designed it this way, unless it was to try to give the transistor a signal during the test. What this means though is that it is important that the 10uF capacitor and the 680 ohm resistor be in good condition to be able to get accurate test results for the transistor test since the capacitor is being used outside its normal operating condition. This is also why it is better to use a germanium diode which has a higher resistance than a silicon diode. A silicon diode will inject more transient charge current into the capacitor which can reduce its life compared to a germanium diode. Luckily from my experience the capacitor seems to survive this abuse. Unfortuantely, the choice of the carbon composition resistor has been a problem in that they seemed to have selected a supplier that produced resistors that fall out of spec over time, which happens with some carbon composition resistors. So be sure to check the resistance of the resistor as a part of the restoration process. See the eico666-667-repair.txt file for additional information on how to properly measure the resistance. Also, the line adjust only works when the Transistor Test switch is in the Tube position. Always adjust the line control first, then you can switch to the transistor test selection. An incorrect line adjustment can cause erronious test results for the transistor test. Note: I have seen references to replacing the 10uF capacitorss with larger values. In a word; DON'T. Especially the capacitor on the transistor test switch. The transister test is designed around that capacitor being 10uF. Changing the value will change the test results. In addition, the circuit uses a germanium diode as the rectifier putting in a large capacitor can stress the diode. If you replace the germanium diode, then use a germanium diode, not a silicon diode. As with the capacitor, putting a silicon diode in the circuit will change the test results. For the same reason, the capacitor on the line calibration power supply should be 10uF as it will stress the selenium rectifier. I've also seen reference to the selenium rectifier going bad. Unless the rectifier was stressed, they generally don't go bad. Most cases of "bad" selenium rectifiers is simply an issue opf not knowing how to test them. They have a higher turn on voltage and will not show the expected low forward resistance reading on most Ohm meters that a silicon diode will show because of the higher threshold. If you measure 70VDC on the line calibration power supply, then the selenium rectifier is working. For more information on replacing the diodes and capacitors, see: "eico666-667-repair.txt" The two replacable items in the 666/667 testers are the fuse and the pilot lamp. As long as you are doing a restoration, you may want to replace the pilot lamp. The pilot lamp is a type 47 (6.3volt 0.15A) located just above the meter. This lamp tends to burn out rather quickly. You can replace it with any small bayonet 6.3V lamp, although I wouldn't use anything more than 0.15A as they will burn out even faster and will place an added load on the power transformer. You can alternately use a higher voltage lamp such as 14volts (1813 or 1815), which will make the lamp last much longer (as much as 10x), but it will also reduce the brightness of the lamp as well. There are also some led replacement lamps starting to show up (or, you can make your own using a dead small bayonet lamp). Using an led would mean never having to replace the lamp again in most situations. The lamp is not required for the tester to operate. It's only real purpose is to let you know that the tester is turned on. So if you don't have a replacement lamp and can't get one, don't sweat it. The lamp is not required. It is just a visual power on indicator, nothing more. The fuse for the 667 is accessable on the front panel, so you don't need to pull the tester from its case to access it. On the 666 the fuse is inside, mounted next to the power transformer. I have never had the fuse in the 666 tester blow on me, so having it located inside is not a big problem that I can see. Charts: The last chart Eico made for the 666 tester was 666-09. (The last I've ever actually seen is 666-07). The later charts corrected a few errors and changed the way most dual triodes were tested (making the test more cumbersome, but more accurate as well). The most common chart found in the 666 tester is the 666-05 chart. Care must be used with this chart as it has a number of errors. In some cases it is serious enough to destroy the tube. However, some of the errors were carried foreward to the newer charts as well, so be careful and alwasy verify the values, especially the filament voltages. The type 34 tube is listed as having a heater voltage of 8.0V, however this tube has a 2.0V heater, setting it to 8.0V will burn out the heater in short order. The type 35/51 tube is listed as having a 25V heater. However, this tube actually has a 2.5V heater. That dropped decimal point will cause the heater to instantly burn out if you set the filament switch to the specified setting. The same problem occurs with the type 57 tube. It is listed as being 25V, but the actual filament in the tube is 2.5V. The type 816 tube is another one with a dropped decimal point. The chart says 25V, but it is really 2.5V. Always check a tube manual for the correct voltage setting rather than relying on what the Eico chart says. They had good electrical engineering, but their document quality control was bad. The last Eico 666 chart I've seen that was published was produced by Coletronics in 1978. It appears to mostly be a copy of the 666-07 chart. It does not have the old preoctal tubes listed, so you will need to find a copy of an old Eico suppliment chart to get the setting for the older tubes. However keep in mind that the settings have some errors. The filament voltage errors listed above are the most serious ones that I know about. If you note those on your chart, at least you won't blow up those tubes if you try to test them using the original stated chart values. Over the years I've found many of the settings on the Eico to be less than optimal for the tube being tested. In some cases the setting will show the tube to be much better than it really is, in other cases it will cause a perfectly good tube to be shown as being bad. I have my own "tweaked" chart that I use and have been periodically threatening to make an electronic copy of it and providing it to the rest of the world out of the frustration with the charts supplied by Eico. Testing Unlisted Tubes: Eico also has in its manual a procedure on how to develop test settings for tubes not listed in their charts. While these settings are a good place to start, don't rely on them to give you a valid test result. The only valid way to determine the test settings is to get a known good tube that has been tested on a known good calibrated tube tester. Myself, I use a calibrated Hickok 533 tester as my reference. I then average the readings from ten known good new tubes (if I can find them) to get my reference setting. Another important thing to know is that tubes have a wide range of varience in the readings +-10% is normal, and some tubes have even wider range of readings (such as pentagrid converters). They can also have significantly different results depending on the tube tester they are being tested on (pentagrid converters are particularly a problem). Most manufacturers target a tube at 110% emission when new, with a tolerance of +-10%. Although some had even higher tolerances, some running over 140% emission. The tightness of the tolerance depended on the intended use for the tube. The good manufacturers would sell the tubes that fell out of the tolerance range to the second tier sellers who would relabel the tube and sell them under their own brand name. The important thing to know is that even a new tube can have a wide difference in the test result from the declared average perfect tube. There is nothing wrong with the tube and it will last just as long. However since people don't like to see a tube that shows a test result 'below' the perfect average setting, the tube manufacturers set the "average" test results to actually be the low end of acceptable test results for a new tube. What that means is that the vast majority of the tubes tested will fall in the 110% to 120% test result area. People feel much better about test results between 110% and 120% rather than 90% to 110%. There is no real difference, it is just playing games with the numbers to make people feel good about what they are buying. This varience even shows up in "good" testers like the Hickok tube testers. Early test settings were developed for the average result of a new tube. However people complained when their new tube measured below the average result. "Your trying to sell me a used tube as new!" As a result, later test settings were developed to be at low end of acceptable for a tube. The importance of knowing the variablity and the target they try to build towards is knowing how that reflects in determining the settings to test the tube. To transfer the measurement made on a calibrated Hickok tester (which provides a reading in micromhos) to an Eico, divide the measured micromho reading by the average reading from the Hickok chart. This is the percentage you will setup on the Eico. (eg if the Hickok reading is 110% above the target reading, then set the Eico to read 110 on the scale. This is not overly accurate, but will at least give you a good idea of the condition of the tube. An alternate approach requires more skill and knowledge of how to set up the test. Get a known good new tube that is in the center of "new" readings. Then setup the Eico to show the reading at 110% (or offset the reading by how much the tube differs from the ideal average tube). Getting the readings will require setting up a test jig or using a curve tracer to determine the characteristics of the tube in question, and understanding how the results relate to the appropriate documents for the "ideal" tube. Since most people don't have the equipment, knowledge or skills to do the later, it is much easier to do the former and transfer the readings from a known good calibrated tester. Assuming of course that the settings on the tester being used as the reference are correct as well. You should keep in mind that some tubes are particularly difficult tubes to test. Pentagrid converters are in this class of tubes. Tube testers do not normally have the circuits to properly test these tubes. Pentagrid tubes are normally operated at radio frequencies with high impedance circuits. Further an important aspect is the interaction between grids of the tube which is how it performs its work of converting the high frequency RF down to the intermediate IF frequency. In addition, these tubes are normally not running very hard, so they can operate at lower emission levels than other tubes and they can deal with a much wider varience in tube gain. The result is that the readings for these tubes are more variable, and the acceptable operating range is much wider. Thus it is not uncommon to see pentagrid tubes as much as 150% gain or more above the average declaration. Test settings for the pentagrid tubes can vary. Some of the early settings specified for the Eico applied filament voltage to the signal grid in an attempt to measure the grid interaction. I have not seen this to be of much help, and it tended to result in irratic test results. In my revised test settings I revise these to more "normal" test setups. Just testing the cathode emission on a pentagrid converter is probably the most useful test. Attempting to try to test it's functionality will likely just cause more confusion and most likely declare a perfectly good tube as being bad. Power tubes can also be difficult to test. They can require high filament current and/or high plate current to properly test these tubes. Most tube testers will not properly test these tubes as they can not provide the voltage and current levels that the tube normally operates at. As such any test result is really only going to tell you that the tube is not yet dead, but it may not tell you much about how much life is left in the tube. For more detailed information on testing tubes using the Eico 666/667 testers see http://www.fourwater.com/files/eicotesting.txt Calibrating the tester: This is very easy to do, all you need is a voltmeter. Check that the Filament and Line Adj control knobs are placed correctly. Turn the Filament control fully counter clockwise (towards zero). The knob pointer should be pointing at the "0" tick mark. Turn the Filamant knob fully clockwise (towards the "Z" tick mark). The knob pointer should be pointing towards the "Z" tick mark. If the Filament knob is off by more than a small fraction of a tick mark, then it was probably installed incorrectly on the control shaft, or the control itself may be improperly positioned. Turn the Line Adj control all the way clockwise. The knob should be pointing to "105". This one is not as critical as the filament knob as long as the tester was calibrated with the knob in that position. If you change the position of the knob, then you should recheck the line cal calibration. It's possible that the Line Adj control may have been replaced with a control that doesn't have a locating tab, or a flat area on the shaft. In that case, turn the control all the way clockwise, make sure the mount nut is tight, then place the knob on the shaft with the pointer pointing to the "105" tick mark and tighen the set screw. Periodically check the knob position as without the locating tab and flat on the shaft, the knob may become misaligned. Normally there is a locating tab on the Filament and Line Adj controls that goes through a hole in the sub-panel, which causes the control itself to be correctly positioned on the panel. The control shaft has a flat area on it that the set screw in the knob is tightened against. That normally holds the knob in the correct position. It is always possible for an inexperienced kit builder to force the control installation incorrectly, sometimmes maybe even cutting off the tab to force the control to be mounted incorrectly, although they would have to be really ahh...inexperienced to do something like that. A more common mistake is that the knob set screw is not tightened against the flat area on the control shaft. It is especially important with the filament control that the knob is correctly aligned since you want the knob pointing to the correct filament voltage. The Line Adj control is less important. As long as the tester is calibrated with the knob in it's current position, it will work perfectly fine. Check that the knobs on the plate and grid controls are placed properly. To check the grid control knob, rotate the grid control fully clockwise (towards the "100" position). The knob pointer should be pointing to the "100" tick mark. If it is not, loosen the knob and move it so it is pointing at the "100" tick. You loosen the knob by using a small flat blade screw driver to loosen the screw located at the opposite side of the knob from the pointer. After adjusting the knob, retighten the knob screw and rotate the knob fully towards the "100" position to verify that it is now pointing at the "100" as the end stop. Rotate the knob counter clockwise towards the "0" position. You should feel the switch start to make at or just before the "0" position. The knob will normally rotate slightly past the "0" position about 3 to 4 tick marks distance when the switch is activated. To check the plate control knob, rotate the knob counter clockwise to the "0" position. The knob pointer should be pointing to the "0" tick mark. If it is not, adjust the knob so that it is pointing correctly (see the note on adjusting the Grid control knob above). Rotate the knob clockwise towards the "100" tick mark. It should stop at approximately the "100" tick mark (plus or minus a tick mark or two is ok). If it stops significantly before or after the last tick mark, then the plate control is not the proper control for the tester which will result in incorrect test results. Note: The plate controls used on some of the 667 testers don't match the tick marks on the front panel. It will rotate past the 100 position by 3 or 4 tick marks. That can cause a slight error when testing tubes that are sensitive to the plate setting when set at the higher plate control setting (above 90). Not much that can be done about it. I suppose you could compromise and try to set the knob to have the equal offset at both ends of the scale, but then you increase the error at the lower settings. So there is no good solution, But the error is small, less than 5%. Calibrating the line and leakage controls: With the tester unplugged and in normal operating position, adjust the meter needle to zero position using the mechanical adjustment on the face of the meter. Note: The Eico Tube Tester meters are sensitive to static build up. Touching the meter face can inject a static charge into the plastic which will disrupt the meter reading. Some meters have a black conductive paint along the lower edge of the meter to try to combat the static build up. Unfortuntely, it doesn't work very well. If the meter needle doesn't return all the way to zero, it may be that the plastic meter face has a static charge on it. Always make sure any staic charge is disipated before doing the mechanical adjustment on the meter needle. The best defense is to keep a small spray bottle of anti-static cleaner handy (such as you sometimes get with a new pair of eye glasses - anti-static computer monitor spray works too). Spray the meter face with a very small amount. Warning! Don't saturate the meter face, or it will seep inside the meter through the mechanical needle adjustment. Only use a small dab. If the spray you are using comes with a cloth, use that instead of spraying the meter directly. You only need to spray a very small amount, and wipe it off with a cloth. More is not better. If the meter face is cracked, it would be better to lightly dampen a cloth and wipe the meter face with the cloth instead of spraying it so that the spray doesn't get into the meter through the crack. I recommend spraying a very small dab of the anti-static spray on the meter face (or wipe it with a cloth as noted above) before you start the calibration to insure the static charge has been drained from the meter face. Again; Do NOT use an excessive amount. More is NOT better. You only need a small amount to bleed off the charge. If you see the needle drop back to zero when you treat the meter face with the anti-static spray, that is an indication that is was being affected by a static charge buildup on the plastic. Remember; Just touching the meter face with your finger can inject a static charge into the plastic which will disrupt the meter reading. Removing the tester from its case: How to safely remove the tester from it's case. Remove the 14 screws (6/32 by 1/4 inch panhead sheet metal screws) around the outside edge of the tester. (Don't remove the four screws next to the paper scroll knobs, they hold the paper scroll assembly to the faceplate.) Set all the levers to position "1". Holding the front panel firmly to the case, carefully turn it over and set the faceplate on a cushioned flat work surface. Now carefully pull up on the case. You will probably need to wiggle it a bit to clear the wires that will likely stick out a bit. You now have access to the electronics and can proceed with the calibration. ***WARNING*** Caution! Be careful, there are lethal voltages present and exposed with the tester out of it's case. If you don't know what you are doing or feel uncomfortable doing the calibration, get a qualified technician to do it for you. ***WARNING*** Press the reset button to release all the push switches. Set all the levers to position #1. Set the grid and plate controls to 0. Set the filament switch to 6.3. Set the Transistor Test switch to "Tube". Connect the voltmeter across the 130Vac connections of the power transformer. Normally these connections are at the power fuse for one side, and the outside connection of the line adjust control for the other connection. When the control is centered, you will see around 130Volts +-10volts, depending on the provided line voltage. Start with the Line Adjust control in center position (120V), then move the line adjust control until the attached voltmeter reads 130 volts. Note: You must adjust the R7 (Leakage Calibration) trimmer first. The R18 (Line Calibration) trimmer position is dependant upon the R7 setting. Press the "C" push button so that it latches. Touch the cap lead to the chassis. Adjust R7, the Leakage Calibration trimmer which is next to the Filament switch, so that the needle is on "0" of the inter-element leakage scale of the meter (ie full scale deflection on the meter). Press Reset to release the "C" button and stop touching the cap lead to the chassis. Press down and hold the "Line" button. Adjust R18, the Line Calibration trimmer which is next to the "Line Adjust" control, so that the meter needle is centered over the Line Adj mark at the center of the meter. You are now done calibrating the tester. Unplug the tester and remove the voltmeter connections from the tester. To place the tester back in it's case, the tester should be sitting on it's face. Make sure the case handle is on the end of the tester where the roll chart is located. Carefully place the case on the tester front panel, being careful to not get any of the wires pinched between the front panel and the case. You may have to wiggle the case a bit to achieve this. Holding the front panel firmly to the case, carefully turn it over and put the 14 sheet metal screws back in the front panel to attach it to the case. That's it, you are done. You now have a fully calibrated and functional tube tester. Note: If you cannot get the meter zeroed with the leakage calibration, or centered with the line adjust calibration, the adjustment controls R7 and R18 are probably leaky due to dirt and grime on the control. The controls should be cleaned or replaced. See the restoration section above on how to clean or replace the controls. If the Tester won't calibrate properly, see the files eico666-667-repair.txt and eico666tester-meter-check.txt to find out how to troubleshoot the problem. It should be noted that the tester can pass the calibration procedure but still not test tubes properly if there are other problems, such as a bad grid or plate control which are not used during the calibration procedure. See the file eico666-667-repair.txt for information on how to repair the tester if it still is not working properly. (It also tells you how to fix sticking push buttons.) I also recommend reading eico666parasitics.txt which describes a potential problem with the Eico testers causing incorrect readings. Short answer, get the lastest setup charts for the tester. - Search for BAMA : Boat Anchor Manual Archive You can also find the Eico manuals there. Also see the companion files: http://www.fourwater.com/tubeinfo.htm http://www.fourwater.com/files/666-667-mod.png http://www.fourwater.com/files/eicotesting.txt http://www.fourwater.com/files/eico666-667-repair.txt http://www.fourwater.com/files/mutualconductance.txt http://www.fourwater.com/files/eico666meter-power-notes.txt http://www.fourwater.com/files/eico666tester-meter-check.txt http://www.fourwater.com/files/how-eico666-works.txt http://www.fourwater.com/files/eico666parasitics.txt http://www.fourwater.com/files/testertypes.txt Visit us at http://www.MDBVentures.com - Great prices on great tubes!