:B&K 747 circa 1975, Call sign: K5jxh
Here is my best tube tester, (100 % full inpections are first, for damage, smoke shoot signs, or tampering evidence)
I connect my meter to Socket 1 (6AU6 default) pins 3 and 4 (pin 1 is on clockwise side of gap, looking from tops side) I set my DMM to 200vac range and check the HEATER knob on every point, for correct voltage. (mine failed)
When I got it , it had 15 transformer wires, connected to the wafer switch wrong, so that only 6.3v tubes worked and for sure 12v tubes FAIL (was 2.3v), and most others , in fact would blow some tubes up, if I trusted it.
In fact, the 1volt tubes were at 17vac heater power, ouch smoke city. (I expected all this, after 42 long years of abuse, I expected to fix lots of things, and did) See my TIFF schematic for hints on this failure (in red) As I learn more , it lands on that Schematic.
But ,Once the dust and grime, was removed, off top and case, it looked like NEW. ( love at first site, this moment !) (I have ham gear and test instruments that use tubes)
I did the factory calibration last.
I checked all wiring and all resistors inside, and the bias resistors even more carefully, with my trusty DMM , any will work , you do NOT need any relic VTVMs ever.
I then take my BOGEY tubes and check Gm , and all read perfectly. (I did the calibration, but found out it was still perfect, )
Test 1: Turn it off and make sure the meter is at 0, if not adjust that black meter top screw to needle = 0., now turn it on and the meter holds 0. if not , then R10 pot has been bumped, so do step "E" first in the manual, seen below left. 100meg ohm resistor grid emission CAL.
That top panel is aluminum.
It will not rust, but would corrode if put in saltwater for months, and the bottom side is plated in white anodized treatment. I'm mounting the fuse properly here, now. (was wire twisted on, zero solder, jury rigged)
The Ferrite sleeves seen above are for blocking Parasitic Vac.tube Oscillations and then for sure getting wrong Gm readings. Heck my Heathkit SB104 is full of them too, for the same reasons. (all amplifier tubes love to become oscillators, it's your job to prevent it, or B&K's)
The beauty of this tester is the quality and the lack of super complex wafer switches.
The more sockets on a tester, the faster it is to use and the less wafers needed and are then vastly less complex.
Questions seen on forums on topic.
"The B&K 747 adapter, a male octal plug, a small box 4, 5, & 6 pin sockets.
Wire octal plug to same pin on each socket that pin 1 to pin 1 etc.
Use the tester banana jacks P & G for grid cap and for plate cap.
Find a 1950's data book RC-15 to RC-17 or use the web. (me,watch out some tubes 1938, ran 2.5vac at 1.5amps filament and your tester my not be able to muster that current, #45; case in point)
Most 4, 5 and 6-pin tube have an octal electrically identical tube.
Like a #78 is a 6K7 octal set the B&K 747 sensitivity control for a 6K7. ( me, a 1937 tube it is, #78) I'd say there are few people on earth messing with 1937 old old radios made of WOOD. (they burned houses down then easy with this radio)
Set switches 1 to 6 for tube part being connected to.
Switches 7 through 12 and pins that have N/C to the dot.
Set switches 13 and 14 to the electrically identical tube from B&K data sheet.
Make sure that you read the entire manual. (on old tube)
The B&K 707 and 747 are the only B&K tube tester that will test each section of a dual section of a separately. (me, super easy with one flip of a lever, like a 12au7/6AU7 in socket 7)
So tubes with identical sections can be checked for balance between sections."
One can do tube simulations using these free tools.(fun)!
A tube gif simulation , crude but cute.
As you can see it's an inverter and an amplifier. The tube is an electrostatic device. It can turn totally off , or when fully on, has Rp value resistance that is never ever near zero like some FET transistors can do easy.
We also say the output is 180 degrees out of phase with the input.
We know in physics that like charges repel and opposite charges attract, so the plate attracts the electron cloud from the cathode and the grid can block this with its negative charge.
The cathode is chock full of Barium and emits huge amounts of free electrons when hot, and is called thermionic emissions. (my transmitter tube uses thorium in the cathod, to the same ends )
A tube acts like depletion mode, MOS FET. (with a high voltage spec. and higher turn on resistance) talking to young folks never seen a tube ever.
My tester is one of the last ones ever made in the USA. My schematic is here (now with Filament wire colors, added and other tid bits...)
With super simple calibration steps, using any meter. 15min. work .
If you don't like my TIF formatted schematic file, load it into paint and save as JPG or what ever you like.
Manuals 1 and revised for errors
Tube data in one zip file.
CALIBRATION , is super simple.
The 5 steps on page 27 cover this.The book seen top left in the photo above.
The tube socket 1 is uses, and you need to find 2 wires that fit there so they are not loose. (0.040" or AWG wire #18 wire matches perfectly not too big or loose) We use jumper clips to do all tests. (all shops have these parts)
Mouser.com has all these parts for under $2.bucks.
In each step page 27-28 A to E, the power is turned on. The book below corrects one error. (push button test 1 , missing in text)
See the kit here
The book is here, the pots are here.(aka, calibration trimmers)
See the kit here and some 18gage wire to fit into socket 1 and fit good. As you can see it takes $25 in tools and 15minutes work and 5 steps to do, (if 200vdc Scares you, then pay $250 or someone to do it on fleesebay.)
No need to be scared, make the connections first, no power, then power up and do the test, then power down and repeat. Use an insulated screwdriver to turn pots, with little risk to you. (use one hand and keep other in your pocket , turning pots)
The parts are always here (of kit) at MOUSER.com, my favorite store.
The 100meg ohm is a whopping 41 cents link above goes there., the 1meg, is 10 whole cents there, the cap might cost 50c to a buck and same with that 5watt resistor.
The 1uF is minimum, 10x more uF is ok. even more. the 200v limit is due to 200v plate voltages there.
Please take all precautions around 120vac line power, and 200vdc inside the gear, do not work on equipment until you have say a days worth of electrical safety training.
version 1. 1-01-2017