One feature that makes B&K tube testers one of my favorites is that they are the fastest to 'set up', and nearly all can test each triode of a 12AX7 with the push of a button. Likewise, checking out the triode and each diode of a 6AT6 is as simple as pushing 3 separate buttons; each button tests one section of multiple unit tubes. B&K made CRT testers/rejuvenators with 'earlier' model numbers, but I'll concentrate specifically on the receiving tube testers. Below is an example of the B&K500, a quality transconductance unit from early in the B&K 'evolution'. The Model 500 is a little different in that this early unit combines similar tube sections (as in a 12AX7, say) for transconductance tests, something I don't know if I feel comfortable with. The manual states that the 'combined' transconductance is carefully calculated for in the recommended reading, and one weak section would affect the overall reading. I would still like to be able to check each section individually, but I have to admit the idea seems to work. You can't test a 12AX7 any faster than on a B&K 500. The October, 1955 issue of Radio & Television News heralds the arrival of the B&K 500, proclaiming it to be "...specifically designed to be taken into the house where a rapid check of all receiver tubes may be made. In this respect it will not only pin-point tubes which are definitely bad, but a special life test will also reveal those tubes which are on their way to becoming defective." Mention is made in this article (and not a paid advertisement; or is it?) that the B&K 500 will test some 400 tube types. A mystery to me is some B&K 500 tube testers I own have a Fender-type jewel lamp for an on/off indicator, while others have a variable potentiometer to set the grid emission sensitivity! Those testers that have this adjustable control (and seen on one of my B&K 675's) also use a plastic 'acorn nut', so the control cannot be adjusted by mistake.
As soon as the patents had expired on the Hickok mutual conductance circuit, B&K developed a similar setup, but with a few twists. The standard tube compliment in this era and evolution of B&K tube testers is an 83 rectifier and a 6AT6 triode/dual diode, as opposed to Hickok testers with an 83 and a 5Y3. This tester sets up pretty quickly, and the Fender-style selector switch takes you through the tests; Shorts, Grid Emission, Transconductance, Gas. You can calibrate the unit to 'fail' tubes that have a higher leakage than the factory setting. I suppose someone wanted to test each section of multiple-section tubes (12AX7, 6SN7, etc.) individually, so B&K took the hint and released the 550. In this 'updated' tester, the tube compliment is an 83 and a 6BN8. It is easy enough to tell the two apart; the 500 has the meter in the bottom-right corner, and the AC cord in permanently mounted to the upper-left corner. The 550, on the other hand, has the meter in the bottom-left corner, and a removable AC cord(?) is mounted on the bottom-right corner. Also, the 500 has but 30-some sockets for testing; the 550 has 51 sockets. An adaptor panel is available for the 500 (as seen above), to add 16 more test sockets. My B&K 550 is seen below. The 'strangest' part to the B&K 550 (at least to me) is the omission of an on/off switch!
B&K still made emission tester during this time, and an early chronological model number is the B&K 600. An example can be seen below.
The Model 600 is only slightly better than a basic emission tester, where the 'A' control acts as a quasi 'load' setting. Here, there is a 6BN8 under the panel to do the grid emission testing. This is a very good test, and a better 'gas' test than many other testers use, but it is still an emission tester. B&K adopted a new color scheme during the 1960's, and here we saw the tube testers covered in a blue vinyl, with a blue colored panel. This held true until the 1970's, where the panel and vinyl switched back to a black color. Almost immediately, the Model 600 was superceded by the Model 606. An example of the B&K Model 606 can be seen below. The 606 moved the meter over to the right side of the panel, and added a couple of extra sockets for testing 'new' tubes, but all else is essentially the same.
This B&K 606 is a popular tester to find with old TV repairmen; it is so compact and easy to set-up. It should appear obvious that with the tubes for the oscillator and rectifier under the panel, we must have a larger chunk of real estate to park these extra circuits; you cannot have a compact transconductance tester. A tiny 6BN8 is still under the panel for the 'gas' test called 'grid emission' by B&K. Compact and simple set-up testers are always indicative of emission testers. Note also this tester is named the 'Dyna-Jet', while the transconductance testers are usually labeled 'Dyna-Quik', save the Model 600. I still can't see much of a difference between the Model 600 and the Model 606, but I have heard a rumor that the Model 606 had a regulated heater supply. I do know that the controls are identical; a heater setting, a 'Load' control ('A'), plus two other rotary switches to help configure the socket.
The transconductance-tester Model 550 was superceded by the B&K 650, a larger unit that sets up and tests tubes pretty well the same way as the 500 and the 550. Below is my B&K 650. Note again the tester is labeled 'Dyna-Quik', and the period-correct black vinyl and panel markings. The October, 1957 issue of Radio-Electronics announces the new arrival of the B&K 650, mentioning such features as "instantaneous heater continuity check.... tests each section of multiple tubes for mutual conductance, shorts, grid emission, gas content, and life."
Another unique feature to the Model 650 is the option of setting the 'Sensitivity' setting to read the transconductance of the tube as 'Good' or 'Bad' compared to average tubes of that type, or reading the actual transconductance of the tube. I'm not sure why they do this, but I seldom use the 'Actual gm' settings; the 'Good' or 'Bad' settings are marked on the panel, so it's easy to set up, even without the manual. Here, each section is tested individually via a switch that resembles a Fender pickup selector switch. Position #1 is a 'shorts' test, position #2 is a grid emission test, and the remaining positions on the switch each test one section of multiunit tubes. A real nice tester; it also has a transistor test function, and a handful of tube sockets which are not wired up, but have the capability of being wired for 'new' tubes to arrive after you've bought this unit. Under the hood is once again an 83 rectifier and a 6AT6 used as an amplifier to detect grid emission. There are a free pair of diodes included with a 6AT6, and they rectify the AC signal from the plate to be measured by the DC meter movement. The accompanying manual gives a little bit of tube theory, especially on how the 6AT6 is used to measure grid leakage. Without boring you with all of the theory, here is the diagram of how the circuit works.
As it may not be obvious, the tube is biased to cutoff. Should a tube with grid emission/leakage be inserted to test, its leakage current will overcome the bias voltage, and a current will then be measured in the plate of the 6AT6 triode. An interesting idea, and one I believe is a B&K exclusive. Now, onward with more B&K tube testers!
It would appear that I am the only living soul who has the official instructions on wiring the 610 Panel. As seen in the above picture to the lower left, this panel is used to test 'newer' tubes. This is similar to the set up seen in later testers like the 700. Rotary switches complete the connections, and thus the tube can be tested. If you need the instructions on wiring the 610 Panel up to your B&K 650 tube tester, you can get them by simply CLICKING HERE.
Another 'oddball' tester from B&K has to be the demonic sounding Model 666. I do not own this tester, and this information was passed along to me. A photographic example of the Model 666 is seen below.
Again, there are just a few wired sockets to select, and older tubes (such as and 83 found in many tube testers!) cannot be tested. There are no 'Telecaster' style switches to select each test, just three pushbuttons. There is a 'shorts' test, a 'grid emission' test (now done with a 2N5458 FET!), and the 'quality' test is a simple emission check. From the panel styling, and the black plastic 'briefcase' type enclosure, we can safely assume this tester was manufactured during the late 1970's or early 1980's. That makes it strange to use the model designation they chose, from many standpoints. I'll have to learn more about the Model 666, and pass this information along. Since the owner's manual is labeled '666/606', I can surmise it was an updated version of the 606, much as the 747 was a solid-state updated version of the popular 707.
To help simplify matters, and reduce the physical size of the 650, B&K introduced the 700. An advertisement in the November 1961 issue of Electronics World heralds the B&K 700 as '...a new offer of an obsolescence-proof dynamic mutual-conductance tube tester...' It is labeled on the panel as being a 'Dynamic Mutual Conductance Tube Tester' with no mention of the 'Dyna' tag. No longer testing transistors, and now more tubes with a similar pin-out share the same test socket. Also, the 'Fender' type guitar switch is replaced with push buttons. As you can see, the top 'half' is still prewired with 10 octal sockets. Below, the 'oddball' tubes are selected via the four rotary switches. You must select which pin is the plate, cathode, and grids of any tube you wish to test. Multiunit tubes have to be 'reset' to test each section. Not as fast as the 650, but the tubes that would have to be setup below are certainly not as common as the tubes prewired up top. The tube compliment is now an 83 and a 6BN8 for the triode/duo-diode. The 'compact' idea was even further refined, as seen below.
Here is my B&K 707 (above left); the next step in the evolution of B&K tube testers. It was introduced as being 'new' in the June 1966 issue of PF Reporter. Not much different internally from a model 700 (although the exterior 'blue' color scheme has been adopted), but it is quite a bit smaller physically, and many TV technicians used this model as their 'house call' unit. There are 35 prewired sockets to test tubes for transconductance (seen in the top half of the panel), with settings for approximately 125 of the more popular TV and radio tubes printed right on the panel. Above right is a pretty rare 'black case' 707, presumably during the crossover from the 700 over to the 707. Really easy to use and calibrate, B&K offered adaptors to test newer tubes, and 'empty' sockets are not on this tester. You can probably easily find this tester from any retired TV serviceman; I myself have three of these testers, and 'passed up' a few more. The 707 came with a tube rectifier (83) and a 6BN8. The triode was used once again to measure grid emission. Below is a close-up view of the B&K 707 panel.
You may notice a tube socket on a plate to the lower left of the panel. I said earlier that empty sockets were not included on the Model 707, as seen on earlier models, and this is true. However, to test the new compactrons, the adaptor plate was installed, and the socket wired up to the rotary switches. These rotary switches also set up the other 'stock' nine sockets, all for 'oddball' tubes, and all to be tested for cathode emission. Other than cosmetics, the B&K 707 is identical to the Model 700. The tubes under the hood were eventually replaced by silicon diodes and a FET transistor for the model 747, another popular B&K tube tester to find. My 747 is shown below. Note that now the 'Dyna-Jet' label is being used again, albeit for a transconductance tester! I have no idea why. There is a Model 747A and a 747B; the differences are minimal. The 747B has a circuit breaker that will 'trip' should a shorted tube be inserted in any socket. The 747B also has a regulated power supply. Either the 747A or 747B is an excellent tester, and calibrates pretty easily. With no internal tubes to replace, these testers rarely 'break down'. When they do, they are easy to repair, as the manual includes a schematic and a troubleshooting guide. The most common fault with any of these B&K testers is a burned out bulb under the hood. These bulbs are actually used as voltage regulators, and are seen in a bridge circuit. Should one of the bulbs burn open (a common occurrence), the needle on the meter movement will swing in a negative direction instead of a positive direction. Dirty calibration potentiometers will also cause the meter's needle to pin 'backwards'.
Cardomatic tube testers were never very popular with service technicians. They were popular with engineers and laboratory folks. B&K made a pair of 'automatic' tube testers, and we'll check them out below.
Here we have the compact Model 675. If you'll note, there is only one octal socket. The 'sandwich switch' under the panel makes all relevant pin connections once a punched card is inserted into the slot underneath the little green indicator at the top. This switching also provides proper plate, screen grid, and bias voltages to the tube under test (although you still have to set the filament voltage and the meter shunt)! B&K advertises you need only 60 cards to test over five-hundred different tubes; I believe them. There was a 'big brother' to the Model 675, and it was the Model 685. My example can be seen below.
This tube tester is a total mystery to me. I purchased it even though it had no punch cards(!) simply because I had never seen (or even heard of) one before, the price was right, and the unit was very clean inside and out. I am scared to death of using Model 675 cards on this unit, so if anyone knows where I can purchase a set, I would appreciate the information. The weird parts goes something like this; the punch cards are only needed for the oddball tubes, whose sockets are in the upper right corner, beside the card slot. These tubes get a simple emission test. 'Normal' tubes still test like a 500, 550, 650, or even a 700. The little Telecaster-style switch still takes you through the Shorts, Grid Emission, Test 1, Test 2, and Test 3 routine. I may punch my own cards, or use a 675 card, to test something like a 12EZ6, and find out what the hell this is all about. The other weird mystery is the tubes underneath the panel. The 83 is seen once again, but now the gas test and grid emission are done with a 18FY6! Why? The only time-saver here is when testing oddball tubes. And you still have to set the filament voltage as well as the meter shunt (labeled 'Sensitivity'). Other card-o-matics, like my RCA WT110-A set everything for you.
You cannot go wrong buying most any B&K tube tester. Even if you don't have the manual, the more popular tubes are listed right on the panel, and someone will surely have the manual to get settings not printed beside the socket. You may not be able to test a 2A3 on your B&K 747, but you can test all of the tubes in your Fender/Marshall amplifier without any trouble. Still, in the end the voltages used are a little short of the B+ found in your average Marshall amplifier, and many output tube troubles show up only at high plate potentials. I still like, and collect, B&K tube testers. To see a page of vintage B&K tube tester advertising, CLICK HERE.
I get a lot of enquiries asking about B&K tube tester manuals and calibrating procedures. To try and help those in need, and also save myself some time and effort, I will post a common owner's manual and calibration instructions. As time permits, I will add to the available models, but they are all very similar. So, if you do need some advice on using and/or calibrating your B&K tube tester, CLICK HERE.