Note: This site and the data it contains have been reposted from an archive of Nolan Lee's original web site by Steve Johnson.


This is a work in progress that I've decided to post to see if there is enough interest in me finishing it.
Yes? No? Maybe? Since I failed Mind Reading 101, you'll have to tell me. I've got probably ten times as much material as is currently posted but hate to spend the time doing this if no one is interested in it. As of today,. I've only had a couple of comments on this page. It's been "up" for a month. This version corrects some spelling and grammar errors and adds additional MX-949 info and some of the information that I have about the TV-7 series bias pot and power transformers.


My Thoughts on the Operation, Calibration, and Maintenance of US Military Tube Testers
Copyright © 2002 by Nolan E. Lee
beta Version 0.12 November 27, 2002

I've been thinking about placing these comments on line for a while. Over the years I've gotten untold numbers of email messages containing various questions about the calibration and repair of tube testers. More specifically, the calibration and repair of various models of US military tube testers.

I don't consider myself a bonafide expert on the calibration or repair of the these testers and I ain't no engineer. But, I do have a bit of hands on experience with a number of different models of them and have calibrated and tweaked a number of them for myself and friends over the years. In addition I have had contact with a large number of people that have had problems that we've "repaired" via email.

I bought my first tube tester in late 1975 or early 1976. It was a cherry TV-7D/U which I still have. After 27 years of hard usage, it isn't very pretty anymore. It looks like an over the hill prostitute and is pretty rough around the edges. The calibration is perfect though. :-) Since the mid 1970's, I'd guess that I've owned maybe 15 tube testers. The greater majority of these were US military surplus testers. I still have all but one (a TV-7D/U) of them which I traded to a friend for a nice I-177-B with the MX-949A adapter box a few years back..


My current "holdings" of operating military tube testers are listed below. Don't bother to ask, since none of them are for sale or trade.

Three of the MX-949A/U adapter boxes for the I-177 series testers
One of the I-177
Two of the I-177-B
One of the TV-2B/U
Two of the TV-4A/U
Two of the TV-7/U
Two of the TV-7D/U
One of the TV-10D/U

The format of this page may change as I add additional material and receive comments and feedback from viewers but for now, the comments will be listed for each of the above mentioned models in the basic order they are listed above. If you have any comments or spot something you think is in error, drop me a note. A lot of the comments for a particular model can apply to more than just that one model so it might be best to read everything and determine if it is.


General Info for All Models


The 83 Tube

The number 83 rectifier tube is a mercury vapor type rectifier that is designed to operate on a vertical plane with the base pins pointing towards the center of the planet. It is supposed to be transported and stored with the pins pointing toward the center of the planet. It's not supposed to be jarred or shaken either. What a wonderful candidate to mount on its side in a portable instrument that gets banged around, huh? Sadly, once common 83's have gotten expensive and can be a little tough to find at times.
One of the things you can do to help extend the life of yours is to always let the tester warm up for a few minutes before using it. Turn it on, set the line adjustment and leave it alone for a few minutes. If the tester has been moved since it was last used, let it warm up for ten or fifteen minutes before using it. This greatly decreases the chances of an internal flashover in the tube from condensed mercury being splashed where it shouldn't be and creating a short. It also allows any splashed or condensed mercury that is on the coated filament to evaporate before nailing it with a B+ load and ruining areas of the the coating which will lower the emission of the tube. Do that enough and you're replacing the tube.
Also, always try to use a "balanced" 83 if you are replacing one. You want one with as similar test values on each of the two plates as you can get. If they are way out, it can cause calibration problems.
Another option is a solid state mod in an old tube base.
<<<add SS mod info>>>


The 5Y3GT Tube

There's not a whole hell of a lot to say about this one other than they should last just about forever unless physically damaged. The ruggedized 5Y3GTWB is the best way to go if you need to replace yours but don't worry about it if all you can find is a regular 5Y3GT. I've got three 50+ year old I-177 testers and a 1953 TV-7 that all have their original 5Y3GT which all test and work fine. Again, as with the 83, try to use a tube where the test values of both plates are the same or at least pretty close. If one is "hot" and the other is noticeably weaker, replace it. If both are middle of the road, leave it alone, the current demands on it are pretty conservative "Balanced" is the key word here. Due to the design of the tester, a solid state modification is not recommended for the 5Y3.

The 81 Fuse Lamp
<<<Insert Picture of 81 here>>>

Accept no substitutes, use a number 81 lamp, period. It's rated at something like 6.5 volts at 1.02 amps. They are available. They were used as dome lamp bulbs in a zillion cars and trucks for a couple of decades. If they guy at the counter asks you what it's for, tell him it is for the dome lamp of your 1938 Buick.
I've had my best luck with ones marked with an "H" by the manufacturer. I don't know who made these but I lucked into a rather decent supply of them years ago for next to nothing. They always fit the panel holes of the testers without the rubber grommets. Some of the replacements do not. If your tester uses a rubber grommet around the fuse lamp hole, you're probably OK. If it is one of the ones that doesn't use the grommet, check to make sure the brand you are buying fits before you buy a lot of themIt's worth keeping a spare or two on hand.


The 49 Bias Fuse Lamp
<<<Insert picture of 49 here>>>

For the tester variants that use a bias fuse lamp, use a number 49 lamp, period. They are rated at 2 volts at 60 milliamperes. They are available and using a 49 rather than some other easier to find lamp can save your bias control. Stick with recognized quality brands for this lamp and keep a couple of spares on hand.


The Power Cord

I use grounded three wire power cords with the "hot" lead wired to the on/off power switch when I replace one of mine.Your mileage may vary.


The Switches

DO NOT blindly spray any of the rotary or pushbutton switches with a cleaning compound. Some cleaners leave a residue that can be permanently absorbed by the switch wafers, tube sockets, and the insulators of the push button switches. I have measured the electrical leakage of junked switch wafers and that I have experimented on by spraying them with certain brands of contact cleaners. Not good. I have also experimented with decontaminating them afterwards. Some could be decontaminated, and some couldn't. Not good either. You haven't lived until you replace the function switch in a TV-7. If you are going to use a cleaner, use one that is totally non conductive and dries with zero residue and even then only apply it to the actual metal contacts using a toothpick or something similar. On the testers with silvered plated connectors, traces of silver tarnish isn't a problem. It's as conductive as the bare metal.


The Tube Sockets

As far as cleaners, take the above comments about the wafer switches and scratch out switch and write in socket. If you replace a socket in one of the later models of the the TV-2, TV-7, or TV-10 series that uses ferrite beads on the wiring, make sure that you leave the beads on the wires. Also, with all models and variants, try to duplicate the original wire layout if you disturb it to decrease the chance of oscillation with high gain tubes. I've only had to replace a few of the front panel sockets over the years. Usually, the existing ones can be "tightened".
On a side note, I've seen one of the under chassis old bakelite four pin sockets for the 83 tube fail. I was getting erratic readings for tubes under test. As it turned out, one of the contacts for the plate pins carbon tracked to the mounting bracket. It was in my old WWII vintage I-177. I replaced that socket with a ceramic one.
The acorn socket used in all of the above mentioned testers can be prone to breakage. Be careful inserting tubes into it. It is also common for the contact plunger in the base of the socket to stick from an accumulation of dust and other crud. I use compressed air and a non residue type electronic cleaner to keep mine free and jiggling.


Socket Savers

It's been probably fifteen or twenty years ago when I ran into my first problem with a socket saver. It was the 7 pin miniature on my old TV-7D. It developed a carbon track on the underside between two of the pins resulting in false shorts indications. I spent probably a half a day tracking that sucker down. Since then, I've personally seen three or four more that have done that and have diagnosed several dozen via email. The carbon tracks were all tiny and looked like nothing more than a tiny scratch. A 16 power eye loupe will tell the tale though along with an ohmmeter. The 7 pin ones seem more prone to this. My guess is that its because the pins are so close together. I've never heard of one of the octal one shorting like this either. I'd be real careful about cleaning the front panel with liquid soaps or water around any sockets that have a socket saver mounted in them. I can see the potential for water being trapped between the socket saver and the panel socket and leading to carbon tracking when the tester is used. Even if the water evaporates it acan still leave conductive deposits behind.
Another thing to check for is the integrity of the pins in the 7 and 9 pin miniature socket savers. The octal ones are made differently and as a result, don't have this problem. I have seen a number of the miniature ones fail. One or more of the four little beryllium copper fingers that grip the pin of the tube under test will crack and break away. I've seen a number of them where all four of the little fingers have broken which can result in very erratic readings for the tube under test. They can't really go anywhere as long as the socket saver is installed but can fall onto or into the tester when the socket saver is removed. Anytime I remove a 7 or 9 pin socket saver I have the front panel angled face down before pulling the socket saver from the panel socket.
Personally, I think that they are more trouble than they are worth since the cost of them has skyrocketed. If they were still cheap enough to where you'd simply replace one with a new one at the first time of trouble I'd use them everywhere. But, they aren't. I've seen them sell for as much as twenty dollars apiece. Because of this I'd rather just change the a panel socket every ten or twenty years with a high quality military or NASA surplus tube socket. Yes, I've had the NASA tube sockets for a long time...


The Meter

I've disassembled and tweaked an untold number of panel meters since I was a teenager. I can't begin to count the number of "sticky" meters that I've fixed using the old "tape trick". I've calibrated the meter movements themselves. I've even removed the glass from the "soldered glass" sealed meters like the one in one of my Supreme I-177-B testers that you can't zero and repaired and calibrated those. My advice is that unless you have a lot of previous experience at tweaking meters to simply leave the meter in your tube tester alone. It's very easy to damage or even destroy one in the blink of an eye while either working on the movement or even checking the FS calibration and meter resistance.

If you want to learn more about meters, find you an old copy of Middletons meter book of 1940's vintage and study it. The name of it was "The Meter at Work" if I remember right. Then score yourself a lighted bench or desk mounted magnifier and wait until the next hamfest. Keep your eye out for few cheap priced or broken meters and start learning. You'll need a dead steady hand so no while working on the meters so don't chugalug Jolt Cola or beer while you're working on one. And no, I don't do meter work for anyone but myself, sorry.

Original meters have gotten scarce. I've been looking for a spare percent quality meter for my TV-2B/U for several years without success. A viable solution is to substitute a different analog meter of the same physical size and electrical characteristics and install the original face on it or make a new face. Padding the total resistance and shunting the meter are simple tricks for getting one to work that doesn't matchup electrically.
Making a custom face or scanning and printing out a replacement meter face on a laser printer is nothing new. There is a trick that a lot of people don't know about. Unless the meter face is a mirrored type, most can be flipped around backwards and the replacement printed face can be cut out and glued to that back side of the original face. Simple, huh?

The best and least expensive thing is to simply take care of the meter you have.
NEVER test a tube for value without performing the shorts test first. Attempting to test a shorted tube for value can be instantly fatal to the bias control and/or damage the meter movement. Always perform the shorts test first.

Another thing to help prolong the life of your meter is to shunt a couple of 1 amp 1000 volt silicone rectifiers across the terminals of it along the lines of the following picture of the meter in my TV-10D/U:

Safe Metering Diodes...

This modification will limit the voltage across the meter to the approximately half a volt junction voltage of the rectifiers. You can still smoke a 50, 100, or 200 microamp meter movement with a half a volt but it takes longer than with higher voltages. Make sure that you test the rectifiers before installing them to weed out open or shorted ones. It's a lot easier to mount the rectifiers on two separate terminal eyes like the picture above if your meter has studs on the rear. Any time you pull the tester apart for calibration of service, test the two rectifiers and replace them if necessary.


The Meter Capacitor

It's a thirty to fifty+ year old electrolytic capacitor. It's old. Even with the low voltage levels that it sees in operation, they can cause a number of problems like "slow" meters. Been there and done that. It took a long time to track down that first one. Replace it with a good quality axial leaded capacitor along the lines of a Sprague Atom. Make sure that you observe the polarity. I suppose a tantalum would work fine also but don't think that I have never tried one. Several people I know have restuffed the original bathtub style capacitors with a modern capacitor and reinstalled them. I have done this but prefer turret studs.


Blocking Caps...

Carbon Resistors

Shorts Test circuit problems

Plate and screen voltage problems

Signal voltage problems

Bias voltage problem

General calibration problems due to incorrect voltmeters being used...

Calculating correct shunt resistors...

Ground loops.

Isolation transformers...


Heat build up in the case...

Cheap $1.00 non destructive and non altering heat fix for bench testers that aren't moved around much.


MX-949A/U Adapter Box
<<<Insert pictures of MX-949 box here>>>

This thing is super if you want to read plate current or filament current. It's also handy for testing tubes that have filament current requirements that exceed the output of the tester by using an external power supply for the filament voltage. You can substitute a different signal voltage/frequency, etc. using a signal generator pretty easily with this glorified "breakout box" too.
The main problem that I've seen with these is that the fifty year old rubber jumper leads have cracked due to age and need to be replaced. If you do replace them be careful with the long terminal strip under the chassis. It looks and feels flimsy. It will, like all old terminal strips, char if you try using too small of a soldering iron and apply heat for too long. Also, do not over tighten the four screws holding the septar socket to the front panel. It can crack it and they are expensive. Keep an eye on the hood for the octal plug too. If it gets loose, it can pull off or pull loose and short terminals on the octal plug together. A good quick fix for a loose hood is a strong high quality self locking tie strap cinched down in the hood groove. That's about it for this little beast.
I've gotten dozens of requests for information on the MX-949 adapter box or something along the lines of "How can I test a 5814A on my I-177 tester?" and usually reply with a message and file attachments of the following two images. One is a line drawing of the front panel of the adapter box and the other is of the schematic for the box. The MX-949 series boxes have always been tough to find. But, it's not that difficult to build a substitute that works as well or better than the original. Another thing to consider while you look at the schematic of it is that unless you need to test 832A's or other Septar based tubes, you don't need to include that socket. The same goes for the sub miniature bases, the loctals, the acorn socket, etc. If all you need to test is octal, 7 pin miniature, and 9 pin miniature tubes, the project just got a whole hell of a lot easier. :-)

Line Drawing of MX-949A/U Front Panel

Schematic of MX-949A/U Adapter Box


I-177 Series Testers
<<<<insert pics of I-177s here>>>

Transformers differences
Circuit differences
Push button switch contact cleaning...
Meter differences
"Best" meter.
Bias pot problems and substitution...
Resistors in non-suffixed models...
Sockets...Bakelite bad..
Range switch breakage problem and warning...
Wiring insulation...
Cap lead...

TV-2 Series Testers
<<<insert pic of TV-2B here>>>

Cap lead insulation....
Bad electrolytic filter caps...
Signal level meter 35ma
Resistors and voltage dividers
Pinched wire and transformer failure warning...
Cracked boards problems...

TV-3 and TV-10 Series Testers
<<<Insert pic of TV-10D here>>>

Calibration problems...
Meter values...
Bias pot problems and substitution
Cooked resistors...


TV-4 Series Testers
<<<insert TV-4 pics here>>>
Wiring warning...
Calibration instructions...
Meter warning...
3A4 tube...
"Grounded" problem


TV-7 Series Testers
<<<insert TV-7 and TV-7D pics her>>>

I've noticed that there seems to be a frequent problem with transformer electrical leakage to ground on the early 1952 and 1953 contract TV-7/U testers from the 93 volt AC input primary windings.This can be very apparent to users of these particular testers if they are still fitted with the original two wire power cord. I've also had reports from a number of other people that have found the same problem. The addition of a grounded three wire power cord will hide the problem but does not eliminate the problem and the potential safety hazards. Ditto for using an isolation transformer. I was lucky enough to get a well used early 1952 contract TV-7/U parts hulk some time back that I removed the power transformer from for experimental purposes. It also had noticeable line voltage leakage to the housing from the primary windings along the order of 6 millamps or so.
The odd thing is that when the transformer was powered down, this leakage wasn't measurable with an ohm meter. With that much leakage, it seems like it would be. I do have a vintage "brute force" hi-pot tester but didn't want to risk damaging the transformer or making the leakage worse in the event of an internal flashover. Been there, done that...
I originally thought that maybe the potting compound was breaking down and becoming conductive like the problem that the CRT HV transformers in the old Tektronix 547 scopes are known for. Prior to the experiment that is... <grin>
After looking at the terminal standoffs and seals on the transformer, I had an idea that maybe the problem was moisture from air humidity accumulating in the transformer from the thermal cycling of the transformer and housing. I was a little unsure about this since the transformer is supposed to be well potted and an ohm meter showed a reading of infinity between all of the windings and the case. Ditto for leakage measurements between the individual windings themselves. I thought that even so, the terminal seals and the potting compound is fifty years old and perhaps gaps or cracks had formed in it. I didn't want to cut it open to find out, so I came up with another idea.
I took a military ammunition can with an air tight lid and drilled a hole in the side and brazed a refrigeration fitting over the hole. I then painted the inside and outside of the can flat black. A few days later, I put the transformer in the can and sat it in the bright Summer sunlight. It didn't take long for it to get rather hot. Then I connected the vacuum pump. It didn't take long to start sucking the the sides of the can inward. At that time, I shut the inlet valve on the pump and shut it down. After letting it bake in the sun for about six hours, I powered up the pump and opened the inlet valve and let it run until it sucked the sides of the can in and the seal failed. Scratch one ammo can...
I removed the rather hot transformer and reconnected it to the variac and adjusted the input voltage to 93 volts and remeasured the leakage. It was in the microamp range now and a fraction of it's previous value. It's been sitting under the bench for probably four or five months now and the measured leakage in still in the microamp range. Maybe it's fixed for another fifty years. Maybe not. I'd appreciate hearing from anyone that has any theories on the leakage problem.
Since removing and reinstalling the the power transformer from a TV-7 type tester is a pain in the ass and I've only tried this one one transformer, I cannot recommend this as a "fix". I also don't know if the "fix" will last when the transformer is eposed to thermal cycling. I suspect that it may not.

Calibration problems...
Range problems..

The Bias Pot
The bias pot used in the TV-7 series of testers is a 4 watt wire wound pot with a very special taper. According to the latest military design and final testing specification for acceptance that I have for the TV-7D/U (MIL-T-12424D dated June 28, 1968) the bias voltage should be as follows:

Snip from MIL-T-12424D

One thing that you should know is that these readings are taken with a meter that has a resistance value of 1000 ohms per volt. This means that the first listed value above, of forty volts for the bias setting of 100, is measured on a 0-50 volt scale of this type of meter. That means that the resistance of the voltmeter across circuit is 50K ohms. The load of the meter for testing the bias setting of 22 is 10K ohms, etc. If you use a modern digital meter with something like a one meg input, you will not be able to successfully calibrate the tester, period. This applies to ALL of the voltage readings.

<insert Mallory production line test procedure here>

Meter subs...


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