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 Tube testers

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Cliff Jones
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PostSubject: Tube testers    November 26th 2010, 11:15 pm

First topic message reminder :

This is just to get this topic started. I have 3 tube testers, a Jackson 636, and a couple of B&Ks.
One being a 747 and the other a 707.
------------------------
I just replaced a resistor in the Jackson that was way out of tolerance and now I can do a line adjust.
-----------------------
I would like to make a tube socket strip for the newer B&Ks to test older 4 and 5 pin tube types on. Oh well another project. Has anyone done this?
-----------------
On another note there are a number of Web sites that do have free Manual downloads for old tube testers.
If you come across those drop me a PM and possibly add them to our Links.
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PostSubject: Re: Tube testers    November 14th 2014, 2:35 pm

I was talking to FrankB yesterday about some tubes he found that seem to be rare, so we got into tube tester anomilies, and I mentioned I had run across this article. He was interested in it so for everyone, I decided to look for it, and here it is.


This was found in a Hickok I-177 tester Manual and it may be wise to follow the advice. study

TB 11-2627-2
TUBE TEST DATA FOR USE WITH TUBE TESTERS I-177, I-177-A, AND I-177-B (PAGE 6)
Note E
The tubes listed below should not be tapped when testing for shorts because damage to the tube may result:
TABLE 2 (AND TABLE 3 WITH ADAPTER KIT MX-949/U PAGE-40)
---------------------------------------------------------
1A5GT 1LB4   1S4/VT-210 3A6GT/VT-149
1A7GT 1LD5   1S5/VT-172 3B7/1291-VT-182
1C5GT 1LE3   1T4/VT-173 3D6/1299-VT-185
1G4GT 1LH4/VT-177   1T5GT  3LF4
1G6GT 1LN5/VT-179  1U4  3Q4
1H5GT 1P5GT   1U5  3Q5GT
1L4 1Q5GT   3A4  3S4/VT-174
1LA4 1R5/VT-171  3A5  3V4
1LA6
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PostSubject: TV-7 Tube Tester   November 11th 2014, 9:27 pm

I may take you up on that, prefer NOS.
I am having problems with the voltage settings, and not knowing if the Power supply tubes are in a good range for My TV-7, I did get #83 from Ernie, He got one for me at $5 and said it was good. but I won't know what its condition is, because of the voltage readings I am getting on the filament voltages settings.

Do you Have a Calibrated TV-7?

I am thinking of trying using the line adjust to get the correct filament voltages as a start.
I am in the process of seeing what percent of error by setting up a spreadsheet. I will then know if its a static error or
I have a space heater and it screws up the line voltage (same circuit as my test bench-but its just on the other side of the wall) It drops the voltage pretty bad from 120.6 down to 115.0, so every time it kicks on, my calibration goes south and I have to reset up the test or turn off the darn heater.

It says on one forum to set the line adjust to set the filaments to the correct value rather than the meter line set point. (which makes more sense to me, What do you think?)

I also read that if the meter bridge circuit is unbalanced then I wouldn't get the correct line set.
So I may have to tackle that, also the diodes could be failing (which I don't think so) but anything is possible. ( I just hope I didn't buy a DUD with a bad Transformer at the tune of $250 No )
Well one step at a time.

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PostSubject: Re: Tube testers    November 11th 2014, 7:01 pm

Cliff,
I have mass 5Y3's if you still need one. Both NOS and used & tested.
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PostSubject: Re: Tube testers    November 10th 2014, 3:57 pm

[You must be registered and logged in to see this link.] wrote:
Hi all,
i have an old b&k model 607 tube tester  and i'm looking for the schematic for this unit  as it does'nt seem to be working properly  At least i should get some decent reading  using a new tube.
Thanks

Jp.
Click Here For similarities of the 607-667 B&K.

[url=http://s285.photobucket.com/user/anagrams/library/BK 607]Try this for Schematic[/url]

[url=http://s285.photobucket.com/user/anagrams/library/BK 607 667?sort=3&page=1][You must be registered and logged in to see this link.]

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PostSubject: Re: Tube testers    November 10th 2014, 3:39 pm

Hi all,
i have an old b&k model 607 tube tester  and i'm looking for the schematic for this unit  as it does'nt seem to be working properly  At least i should get some decent reading  using a new tube.
Thanks

Jp.
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PostSubject: TV-7 Tube Tester   November 8th 2014, 10:33 pm

I have been looking for a DC voltmeter with 1000 ohms per volt for a while, without luck. However My Friend Ernie has loaned me the use of His Westinghouse Voltmeter. Its a rare one to find but is in almost pristine condition.
It has a 260 degree movement, and has 8 ranges, 3-7.5-30-75-150-300-750 Vdc.
It has 3 scales 0-30, 0-75, 0-150
I don't know what the accuracy is but it would work.
It is a type PX-161 Westinghouse. If any one has the accuracy or a manual it would help, thanks.

This one looks similar but without the switch and is not the same ranges.



Now I can get to work on testing and if need be, calibrate the TV-7.
I am also going to follow up on using a digital multimeter with the same tests and note the differences for future reference. In case I can not get a good meter like this.

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PostSubject: TV-7 Tube Tester   November 8th 2014, 10:10 pm

It seems there has been some progress  of replacing a #83 rectifier tube in the TV-177 Tube tester. Since its design and circuits are almost the same and using the same parts and power supply tubes, it would apply to the TV-7 Military tube tester series as well, in my opinion.

Here's a link to ARF Discussion. It has posted the schematic solid-state Tube replacements for both the #83 and 5Y3GTWA that you can build.
Click Here

And here's a good video on that, by demonstration.
You would be wise to store these both for future reference.


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PostSubject: TV-7 Tube tester   October 24th 2014, 8:34 pm

Heh- Heh I will just use tie-wraps as a temporary measure.

-------------

Now my next objective is to paint the case one color. Dove Grey, there are two shades of grey (or gray if you prefer). The case top cover is light gray and the bottom case is dark grey because someone painted over the lighter grey. Another item is keeping the large block lettering intact if I can. I did use a permanent heavy marker to fill in the missing black letters.

I may get a 1/2 pint of black enamel paint and use masking tape to form the letters, the only thing is the letter (D) and the letter (U). That will be a challenge!
study

One of the things on my bucket list is to take all of the Military documentations and organize them into one cohesive folder and actually do the pen and ink corrections. Now That will be a job.

Here's a list of the PDF Documents I have on my computer and forum topics from other forums:

click here english from Greek


Technical Manuals

 • TM 11-6625-274-12,  Operator's and Organizational Maintenance Manual, Test Sets, Electron Tube TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U  Department of the Army, June 1960
---------------------

 •  TM 11-6625-274-35, Field and Depot Maintenance Manual, Test Sets, Electron Tube TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 Department of the Army, 30 June 1960
 --------------------
 •  TM 11-6625-274-24P, Organizational, Direct Support and General Support Maintenance Repair Parts and Special Tools Lists for Test Sets, Electron Tube TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U  Department of the Army, November 1979
--------------------

 •  TO 33AA21-5-32S-1, Operational Supplement, Technical Manual Field and Depot Maintenance, Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U ,  US Air Force, 20 September 1973
-------------------

 • TO 33AA21-5-32S-2, Tube Data Charts  Operational Supplement, Technical Manual Field and Depot Maintenance, Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U ,  US Air Force,  25 January 1978
 -------------------

 • TB 11-6625-274-12 / 1, or US Air Force, TO 33AA21-5-31,  Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U  Department of the Army,  17 January 1962
 
 (This is the basic test data; all the rest are supplements to this list)
---------------------

 • TB 11-6625-274-12 / 1, Change No.1 - Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 Department of the Army,   31 May 1962
----

 • TB 11-6625-274-12 / 1, Change No.3 - Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 Department of the Army,   2 June 1966  This change supersedes C 1, 31 May 1962, and C 2, 31 January 1964
----

 • TO 33AA21-5-31C, Supplement Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 US Air Force, 15 January 1965
----

 •  TO 33AA21-5-31E, Supplement Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 US Air Force, 1 December 1965
----

 • TO 33AA21-5-31P, Supplement Test Data for Electron Tube Test Sets TV-7 / U, TV-7A / U, TV-7B / U, and TV-7D / U
 US Air Force, , 1 March 1975



 Most of these can be downloaded from here:
 http://bama.edebris.com/manuals/military/tv7/





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PostSubject: TV-7 Tube tester   October 24th 2014, 8:21 pm

After I received my tester, I noticed one thing that I wanted to fix right off the bat. That HANDLE!
Of course I had already replaced the power cord.

Mine has one of the correct wire bails missing. Someone had substituted some heavy copper, plastic coated wire and fashioned it to the same form (rectangular) by using two complete turns and soldering the ends together. Of course being copper it was kind of malformed after repeated use.

So I decided to do a replacement. The sixty-four dollar question was, What would work and keep its shape and strength? First I thought of house wiring of 12 gauge. Then I remembered where I had seen some wire stock, it was at a Hobby store! So on one of my trips out of town I stopped by and picked up 3 pieces, one was 3 foot long and another 15 inch pair in a package.

I Removed the cobbled together piece with plier cutters. Then I took the remaining good one apart from the holder, and using it as a form. I used 1/8th brass rod, which worked out just right. I used a pair of pliers and my hand to form the 90 degree bends.

I thought maybe I could solder the ends together, which I attempted, but it didn't work out. So I found this picture I previously had found on the web. I just noticed the assembly as I figuring out how to write this topic tonight. The answer to keeping the wires from spreading apart and possibly damaging the case was before me. Look closely at the handle assembly! Well what do you know!
Two flat formed clips that wrap around the wires and keep them from spreading apart.

I will now get some flat brass or Stainless sheet and form it around the wire. It has/or will solve my dilemma. cheers

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PostSubject: TV-7 Military Tube tester   October 24th 2014, 7:53 pm

PLets Start this topic, first with a video link to using a TV7.



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PostSubject: Jackson 115 user manual   October 17th 2014, 8:43 pm

Here's a link that may not stay very long. So Grab it whilst you can.

Click Here for booklet

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PostSubject: Re: Tube testers    October 11th 2014, 9:34 pm

Continuing- TV-7 notes I read one post in another forum said to be careful if you remove the Fuse Lamp, as the socket is hot and you can accidentally touch it to the faceplate and POOF, there goes your transformer. Some of the units have a rubber gasket in that hole for protection.

I did look at the bulb holder and it is adjustable, up and down, so the bulb won't sit high and avoids it getting hit by clumsiness or tools.

Do not substitute the bulb with anything other than an a TYPE #81.
The Shorts Neon bulb is a #NE-45.

Another thing to keep in mind is there is a GM chart that erroneously lists the last column as going to 60,000 it should be like the previous column 30,000 GM.

Here's a very good link for answering your questions on some things you may not know or refesh your memory. I recommend this highly.

Click Here for TV-7 info.

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PostSubject: Re: Tube testers    October 9th 2014, 3:44 pm

Well I did get a TV-7 that sat on my bench for almost 2-3 months. I just had too much on my plate with my Dads situation and such. I didn't have the mental strength to tackle just replacing the Power cord.
This afternoon I says to myself, it's too important to let it set there and whine for attention.
---------------
So around 1:30 I got up the courage and took my pruning shears and cut the danged old cord off.
Yea! step one.
--------------
I took off the power cord clamp in the case.
Step two.
-------------
Took out the tiny faceplate screws holding it to the case. Just about a gazillion of em Mad
Step three
--------------
The power cord went under the power transformer, The white wire I found out sneaks up to the line adjust POT. I rasseled that wire off the terminal with a soldering Iron and a pair of Hemostats, then used some flush wire cutters to cut through the wrapped on wire. Did the same with the black wire, it was hooked up to the power switch.
Step four 
------------
Now what am I going to do with a green wire? Good question since the original didn't have a ground wire in the cord. Well I hunted for a lug and star washer. I soldered the lug connector to the ground wire, put one of the tiny screws through the faceplate and kind of hung the lug on the screw, set the star washer down on the screw hole and lowered the faceplate down gently, mated the screw-washer-lug and SUCCESS.
Step five
-------------
Replaced all the screws in there respective holes and went round and round till all screws were snugged down.
Step six
-----------
Plugged that puppy in and flipped on the power. OH my Gosh, surprised myself, Power light on and no sparks. Well I be darned, I says and pats myself on the back. only 1-1/2 hours.
Step seven
-------------
Adjusted the line POT to center of meter point. Right on.
Step eight
---------
My next project is to make a load for my Multimeters, to simulate a 1000 ohms per volt meter for testing that tube tester voltages and alignment, but that's for another day.
cheers
cheers

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PostSubject: Re: Tube testers    August 22nd 2014, 12:20 am

Dang it. Read the settings wrong. Tried a couple of other tubes and low readings too. Then I re-read the instructions for the TV-7 and guess what? I was reading the meter wrong. Embarassed 
I was reading each mark as a one(1) rather than as a two(2).
However I ran into another snafu. As I was testing voltages, I got a low B+ reading at the pins.
Now when doing these test your supposed to use a 1000ohms/per-volt AC multimeter, which I don't have, drat! I remember something about simulation of that type of meter load, but forgot the design. Also it was recommended to me to check the testers internal tubes-#83 rectifier and 5Y3. So I am looking for NOs, but on the WEB they are sooooo expensive!!!!!!
So I will rewire the power cord in the meantime for a ground.
WHY OH WHY does this happen to MEEEEEEEE??????????? scratch 

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PostSubject: Re: Tube testers    August 16th 2014, 7:05 pm

Now I can test my HP 606 tubes even though HP recommends just replace the tube with a known substitute. Well until I test my hoard I wont know which ones are good. Rolling Eyes 
So my testing the ones in it, are a quicker solution in the short run. The reason I am doing that I pulled out of my hoard a 1LH4 and it had no response.

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PostSubject: Re: Tube testers    August 12th 2014, 2:53 am

I'm sure you'll love the TV-7 Cliff. It's one of my better pieces of equipment I have at the moment. Though, mine needs to have the contacts on the push buttons cleaned a bit as I need to press down harder than normal to get my readings when using it. At least I hope that's all that's wrong with it.
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PostSubject: Re: Tube testers    August 11th 2014, 7:28 pm

Well Well, I am getting a TV-7 this Thursday. Only $250. top and bottom case halves are different colors, wired hinges and cobbled handle. It was seen by my Friend Ernie as being very clean inside and it works! So He will deliver it to Me. I trust Him as He is Experienced and a Fellow Ham.

I think when I get it I will start to test my tubes that are in my HP 606 sig. Gen.
The modulation meter only goes to 40% so it may be in the bridge section.

If I can get that job finished then I will move  back to troubleshooting the B&K tube tester. If I can get that one up and running then I may sell it. (I need the experience of troubleshooting first)

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PostSubject: Re: Tube testers    April 24th 2014, 11:52 pm

Cliff,
Here is data on the transistor:
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Good source for data on most semis.

Remember the 2n404 is a germanium device too.
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PostSubject: B&K tube tester 747 questions   April 24th 2014, 11:14 pm

To be continued as time permits Me.
I have a question for Those who own the Jackson 747B Tube Tester, with Transistor Q2-2N5818 in place and if your tester is working.

Could you please provide a List your actual working Voltages if Possible?
I do have both the Calibration instructions and the Service manual, but as you know not a lot of Information is provided to overhaul and have all the test point voltages available.

Also please  Identify the ACTUAL location of the Zener Diode on the small Circuit card. Notice that All of the Diodes are set down right on top of the Board so the Identifying Symbol Parts ID is covered over.
I would prefer not to have to Remove each Diode to Identify, because the leads are almost too short. And even the Diagram it self is Shaded out to the point where the numbers are so tiny and smeared they cannot be read at all (only guessed at ).

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PostSubject: RE: B&K 747 Tube tester repair   April 21st 2014, 5:21 pm

A follow up on this tester, one member ( FrankB ) here was kind enough to give me a scan of His 747 manual. Well I declare, it looks like there is a change,

The schematic I have been using shows two transistors, one being Q2-2N5818, that is an NPN and its collector goes first to R-31 (15 ohms) followed by diode D-10 (1A 600V) then to the Pilot Light PL-1 LED then to the filament transformer tap 3.3VAC. On the same transistor (Q-1) there is a diode D-11 (1A 600V) connected from the base to the emitter, also a resistor R-30 (1K ohm 3W) that goes to the Circuit Breaker CB-1 connected from that base and diode (D11)

NOTE: Keep this in mind-it is very important to look at the revision number of the schematic.

This particular design number is 488-104-9-001 M Model 747B ( note the B signifies it uses a circuit breaker)
The second Transistor Q-2  is a F.E.T. Part # 2N5458 or equivalent which might also work for the 2N 5456 on the other circuit revision, I will see if I have any transistor manuals that detail the specs. of Each and post here... It is used to control signal (I could be wrong here) but it has the same function in both revisions.
--------------------------------------------
Now in the next Schematic 488-104-9-001 H also Model 747B ( note the B signifies it uses a circuit breaker).

But Here's the difference (D-10s cathode points toward the 3.3VAC transformer tap) first in line then a 2Volt Lamp (not a LED but a filament type bulb) which is connected to the cathode of a different part number transistor also Identified as Q-2. That transistor number is an PNP 2N404. There is also a diode connected between Q-2s emitter and base but the anode is connected to the base and R-30, which is the same resistance and wattage as the previous resistor mentioned (1 Kohms 3W) the emitter connected to the common return of the filament transformer windings, and of course the resistors end goes back to the circuit breaker CB-1 and other wires. of course both circuit breakers mentioned have on the opposite connection a wire going to the filament Heater) Switch S-5 Note: that switch terminal connection lacks a designation number
So with my original installed transistor it too is even different yet. confused drunken

Wow that took some time to explain, I will post both schematics below so you can visualize easier.

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Schematic reading TIP: I finally took the time to trace the transformer windings for Just the Filaments. In that process I noticed that the switch ( S-5 Heater ) tab numbers on the schematic  didn't make sense to start with, it then DAWNED on me the position numbers related to Actual Filament Voltages! That should help, when you need to reference the Schematic.

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PostSubject: Re: Tube testers    April 14th 2014, 9:57 pm

Very Excellent suggestion. Thanks!

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PostSubject: Re: Tube testers    April 8th 2014, 6:40 pm

The voltages on your tester are not the same as the TV7,10,etc, but should be close enuf to make a test better than a WAG.
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PostSubject: Re: Tube testers    April 7th 2014, 9:24 pm

OK thanks, I know that B&K and the Military had made up the same thing to cover older tubes, but unfortunately they are rare and rather costly. I did look at a couple of supplies for ceramic tube bases and each base socket is usually less than $3 each. So if you cant find a cheap Junker tube tester (by the way that is an excellent Idea) then making your own test strip might be the way to go.

The only problem depending on the good tube tester, would be voltages, because some older tubes from what I understand could be several Hundred Volts, so the tester wouldn't be able to use correct Higher voltages like the Military or Hickok brands. You know DC VS AC on the plates and Dynamic VS Static testing.

One tube tester I have always wanted is the TV7 but the TV2 would do in a pinch LOL.
I have seen how many meters the TV2 has and you would need at least 15 minutes to setup each tube before testing. But of course that would be the Rolls Royce of Testers, pssst I under stand over on the other side of the Pond Their preferred tester is the AVO.

I am slowly working through my B&K 747 because of screwy readings and voltages. I am blowing up the schematic so I can read the tiny print and make a color chart of transformer leads and voltages that aren't printed out. The service manual has some. Of course I have already replaced two transistors and that really screwed things up as far as meter readings. So I will check by removing leads on caps to test and replace and resistors too. It's a real challenge.

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PostSubject: Re: Tube testers    April 7th 2014, 6:56 pm

The old 4,5,6 & 7 pin tubes with 2 large pins. 01A, 26, 57,, etc.
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PostSubject: Re: Tube testers    April 7th 2014, 4:57 pm

I need some clarification! What is a septal based tube?

I have tried to find a definition on several tube sites and dictionaries, but alas have come up short.

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PostSubject: Versatile filament & plate supply T/T leftovers!   April 5th 2014, 2:58 pm

OK, Now you demolished the tube tester to make the test panel for the Septal base tubes,
you have a bunch of junk leftover.

Power cord, transformer, pilot lite, voltage selector switch, etc.

Now leave the selector switch hooked up to the power transformer.
Get a nice chassis box and mount this in the box, putting in a pwr switch, primary fuse, and pilot light. Add some binding posts or banana jacks and you have a nice adj. filament supply for many of those odd voltage TV tubes you wanted to use for something.
NOW-
Make up a bridge rect. and filter assy ( Figure the filter caps for 150VDC) and mount to the output of the fil voltage selector switch using another switch, and adding in a DC voltmeter.
Add output jacks, a bleeder, and you have a nice low current supply, with selectable output voltages.
Good for use as a bias supply, low voltage DC for B+ etc.
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PostSubject: Why didn't I think of it before? T/T mod.   April 5th 2014, 2:47 pm

OK, so sitting here today and reading the post on making a adaptor panel to test the Septal base tubes- and it hit me!
Its so bloody simple Embarassed 

Take an old junk tube tester that has the sockets you need in it. A dead one preferred. (You can usually get them at the hamfairs pretty cheap. Many times because the case has fallen apart. Forget the case- just need the front panel sockets to be in good shape.)

Cut out the panel section containing the needed socket types with a hacksaw, and mount to a casing, wood, metal or whatever.

(The sockets will be parallel wired on almost all testers.)

Add an 11 pin plug on the end of the wiring harness feeding the sockets and the plate/grid caps;(Standard relay plug) and make an extension cable for it using an 11 pin relay socket. Off the socket you put on an octal plug, and 2 plate/ grid cap conn to connect to the tube testers P & G caps.

Sounds harder to do than it is.
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PostSubject: B&K 747 Tube tester repair   March 24th 2014, 11:11 pm

I have been trying to test some tubes for my newly acquired HP 606 Signal generator. I tested three tubes as a start, and every one was very low. I figured something was wrong with the tester.

So I started to look at the Calibration instructions and ran into a problem when trying to adjust a calibration POT. in the second step.
So my voltage reading was between 37 and 50 volts, whereas it should be around 2.5 volts.

Time to do some investigation. Opened the case and removed the unit, turned over and looked for the obvious burned parts, which I could not find.
That's good. Downloaded the Users Manual, Service manual and schematic.

The parts list is incomplete in that the company noted to look on the schematic for part values.

So checking the parts one by one, study  I found that there were some discrepancies. Both Transistor(s) were the wrong part numbers. scratch 

The Q1 is a 2N5456 FET. Which I will remove and test. OH-OH It is a 2N5458 Will have to check that out too! Not even close to the original part Number- I know what happened with that one the printing is so small the numbers could have been mis-read, Its also a  NPN AUDIO TO VHF FREQUENCY DRIVER SWITCH

The Q2 is supposed to be a 2N5818 (Q2 is an NPN Silicon.)
,however, whilst the one in its place is a 2SB370. ( it was a PNP Germanium .)
I did test Q2 but have no definite conclusion as to why it was a replacement. Strange replacement to say the least.

I will post further as things develop and post a few pictures.

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PostSubject: B&K 747 common problem   March 14th 2014, 4:27 am

Found some info on the web:
from old postings back in 2011 on ARF.
I consolidated them to make for easier reading.
Spell check used to correct most errors.

B&K 747 Tube Tester-Calibration step problem

Author Message
ss1965  I have a B&K 747 tube tester & went to do a calibration following the direction's in the instruction manual for the tube tester.  All adjustments work great except setting the bias voltage. After replacing electrolytic cap's & checking the resistor's & diode's for the bias circuit and transformer voltage and all checking o.k. I have the voltage down to -38 volts from - 44 volts, according to the instruction manual it should be 2.5 volt's!! I am new at doing my own electronics' repair but determined to fix this...
I will appreciate suggestion's on this problem!! Thanks' Steve Smile
--------------
jcmjmp   Make sure that your ground connections are nice and solid around the bias circuit. A lot of the connections to ground on these things aren't the best it seems.
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jcmjmp    Another thing to check out is the actual resistance values. On my tester (707),some of the resistors were out by 20% in some cases. The carbon comp resistors are particularly prone to drift up in value over time.
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ss1965     Thank you! I did not think to check the ground connections because the other adjustment worked o.k.!! but I will check that possibility!!
All the resistor's checked close to value's listed on the schematic..I removed each one from the circuit to test them & real surprised that with the age of them they have been good so far...
I guess maybe best approach would be to actually clean the ground at the first tube socket since that is were the measurement for the bias voltage is taken and go from there...
Once again Thank you for the help!!
Steve
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Alan Douglas   It sure sounds as if the bottom of the voltage divider is open.
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ss1965    Like I mentioned I am just starting to try get into electronics' at least do more than just read about electronics'! Could you give me some idea's how to go about checking voltage divider? I am pretty much learning by doing & asking lot's of question's...so I would appreciate all input... Thanks'!
Steve
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jcmjmp  
Do you have a copy of the schematic?
A voltage divider is basically two resistors in series and voltage is taken between the two, referenced to ground.
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dsbk  
 There is a 470 ohm bias-string resistor on the end of the lever switches that goes open on the 747. Use same of higher wattage rating. B&K went to lower wattage resistors at that time, they don't tolerate setup mistakes and shorts as well.
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ss1965
I do have the schematic for the 747
I will look for the two resistor's for the voltage divider, hopefully I will recognize it?(hee hee)
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ss1965  Thanks' dsbk!
I will locate the resistor and check it!
So far I have checked the resistor's on the p.c. board that is in the bias circuit & they were good! changed the electrolytics on the board plus changed diode 8 and 9 because they each had a spot that visually had sign's they had been hot. Even though they checked good on digital meter??
Steve
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dsbk     Going over that PCB with a iron is mandatory. Many bad connections are found there. Look at everything with a lens.
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ss1965   Hello everyone! I am still working on the 747 tube tester as time permit's.
I have taken every component off the p.c. board and tested all are good! getting 120 volts from the transformer.. schematic say's 110 volt's. checked every solder joint, all resistor's checked with in spec... the variable resistor for the bias adjustment I have had of the board twice and checked with ohm meter & is o.k.!! and have not found any shorts but the bias voltage is still way high! using a variac to make sure I have 110 volt's from a.c. power..I still get 38 volt's at lowest setting from variable bias resistor & calibration instruction's say 2.5 volt's d.c.??
And still all other calibration adjust in just fine!!!
This is driving me NUT'S!!
How important is the bias voltage for correctly testing tube's??
Should I add a resistor from the transformer to get the bias down to the 2.5 volt's??
I will welcome all advice!!
Steve
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Alan Douglas   It's been years since I looked inside my 747, but, there ought to be a string of resistors across the bias source, used as a voltage divider. The resistors may be scattered around various tube sockets, but in the end, they're all in series across the bias supply. There has to be zero volts at one end and full voltage at the other. Find that string, measure the voltages, and you'll find the broken connection or switch contact that's the source of the problem.
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dsbk   The 470 ohm on the end of the switch bank goes open often. Bias makes its way back to common thru the signal ballast.
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ss1965    Thanks' Allen & dsbk!
I have replaced the 470 ohm resistor already from a suggestion to check it from one of the earlier post's...there is a wire directly from transformer soldered to variable bias pot on the p.c. board...unhooking the wire and checking voltage from the transformer is close proper out put voltage...but voltage just high at the first tube socket where it should be low?? I have checked all resistor's on the schematic and every thing on the board there is two wire wound resistor's off the board I am going to check still and that will make every resistor in the unit checked...
I will look for voltage divider again dsbk! if I ever figure this out it will probably be something simple! but hard for a newbie like me! Smile
Thanks' again!! I will be on here & let you know if me or tube tester is winning!
Steve
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ss1965   Sorry
I meant I will check for voltage divider suggestion Allen!! I mixed you and dsbk up!!
Steve
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dsbk    ss1965, are you pressing one of the Test buttons while doing your string voltage measurements?
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ss1965   No instruction's said to put voltage meter between pin's 1 & 7 (pin 7 being ground) and adjust bias voltage to 2.5 volt's dc.. but voltage is 38 volt's at lowest setting on pot....i have not checked switch contacts closely but I will...recheck more component's not to many left to check though :)I've been unhooking about every thing an checking trying to find a bad something to fix this tester.. Steve
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ss1965   sorry last post not complete!! meant pin's 1& 7 at 1st tube socket...
--------  
Retired Radio Man  Try the adjustment with test button 1 depressed as suggested by dsbk. The 707 requires this. There may be a goof in the 747 manual. RRM
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It's worth a try! you could be right pressing the button may have been left out of instruction's... Thanks' for the response &suggestion retired radio man... Steve
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dsbk    "Press test button 1" is an item in the procedure. Does your instruction not say that? It should. Look in the back of your owners' manual. No wonder...
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ss1965   I am sorry but I gave you people wrong information! yes I have pressed test button #1 when I was setting bias voltage...and as I said with pot at lowest point it's at 38 volt's.... I answered totally wrong earlier do not know where my thought's were at!!!!
And I am using original owner's manual following calibration procedure...
Steve
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dsbk     OK, when a "Test" button is pressed it measures like this on a calibrated tester (you won't get print voltages):
Point "Z" white bus -19.5vdc, then thru 2.4K to blue bus -7.5 Vdc, then thru 1K to green bus -2.5vdc, then to ballast .07vdc. on a gray/violet wire. These are print colors, occasionally B&K may have used a different color in the build.
The bias string has its' source of -volts at point "Z" (hi bias) and the - of your 10 mfd bias filter is also tied to that point. The + side of that cap is at the ballast point (lo bias).
When testing, the AC drive signal comes from the ballast, and the ballast acts as the return to common for the dc bias voltage divider. The AC signal level is unaffected by the divider and will be 1.5vac everywhere on the string.
You can use a jumper to connect the lo bias (gray/violet) to chassis, and see if the divider is working to give different -dc levels. Do not push any buttons with jumper in place.
You will occasionally find a no-solder on a socket or switch with these testers. A lens helps.
----------  
ss1965   Thank you so much for detailed explanation dsbk! that help's a lot
I will check what you described...I will be working on it this weekend I hope for the last time!! hee hee!
i have to unhook a diode from the circuit and check it out it show's a voltage both direction's it's by Transistor Q2 (2n404) then I will have checked each component singly...
Then I will follow your direction's...and hopefully cure this thing!!!
Thank you very much for your help!!
I will post later this weekend on if the tester or me is winning the battle....
have a great labor day weekend... Steve
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dsbk   That FET Q1 often goes bad too. NTE457. Good luck.
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ss1965   I have to check voltage's that you posted still..... and I understand your instruction's.... but looking at the schematic (more like staring at it) I am not seeing any of the resistor's in the bias showing where they are going to ground!!the schematic is showing ground at the transformer & following the schematic the only ground shown is at c-6 & c-7 electrolytics, but none of the resistor's from the transformer through the bias circuit to the buss is shown being grounded like a voltage divider...how is bias referenced to ground?
My schematic is the original factory schematic ..but dose not show any grounded resistor's???
Steve
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dsbk   Feed at the high bias end. Return to chassis through the signal ballast at the lo bias end.
The 10mfd filter is across those two points. The string is floating when not making a tube test.
Voltages are divided only when a "Test" button is pushed and the lo end gets connected to the ballast. The same -dc will appear at every point on the divider when a "Test" button is NOT pushed. That is why you can use a jumper to chassis at the lo end, thereby freeing your hands for diagnostics. Don't push a button with the jumper in place.
-------------  
Retired Radio Man   The 707 has a 10 meg resistor that is in series with the bias divider. It is part of the gas test circuitry. This resistor is shorted and the low end of the divider connected when a Gm. test button is pressed. The schematic I have for the 747 shows a 3.3 meg and an 18 meg in the same general position. Both of these have to be shorted and the low end connected for the bias to be correct. Open switch contacts in either place will cause the bias to be way off and unadjustable. My schematic doesn't have numbers for the switches but the shorting set is part of the Hi Bias line and the low end set part of the Lo Bias line that goes back to the 1.5 volt signal source. RRM
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dsbk    Thanks RRM, I glossed-over that, and you are right, it may have been a source of confusion.
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ss1965    I have not a chance to check any voltage's to spend any time with the 747 but will since this is a long weekend for me. Following the post you gentlemen have sent( I appreciate your help very much)
1)I need to clip a jumper from the + side of the 10 mfd. cap to chassis for ground. And with out pressing any buttons...have volt meter from chassis ground check voltages at blue buss/ green buss /& at gray / violet wire. And if voltage divider is working voltage's will be at or lower than -7.5 v at blue buss &-2.5 v & .07 v at gray/violet wire...
Am I correct?? I am wanting to make sure I am correct so I do not check voltages incorrectly and mess up 747..worse...
Thank you guy's for help & patience!!
Steve
------------  
dsbk    That sounds right, but as RRM said above, you still have other resistors in circuit that would be jumped-out when using the test button. This is just a fast diagnostic step to see if the divider is working with the jumper.
You may have to look at switch contacts or elsewhere if that test works, and the button test still does not give division.
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mescalero   When evaluating switch contacts, I prefer to do it "live."
This allows me to better determine contact resistance under load. So, instead of powering down and using an Ohm meter, I will put a Volt meter across the contacts, either AC or DC (depending upon circuit properties) and measure the voltage across contacts when the switch is supposed to be opened and closed. Hypothetically, and depending on circuit properties, there should be two dramatically different readings. However, the voltage reading across contacts in the closed state should typically be very, very close to zero.
This works for relay contacts too.
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ss1965    Hello everyone! I wanted to give you an update on my battle with the tube tester..
I have checked the voltage's to see if the voltage divider is working as was described in the earlier post's.
With jump wire from + side of 10 mfd. cap to ground..
-009.5mv at blue buss...(7.5v)
-003.0mv at green buss(2.5v)
-000.0mv at the gray/violet wire (lo bias)(.07v)
I guess I need to follow the gray/violet wire back and see what I can find at other end?
Steve
------------
dsbk    OK - you are getting close then. You have your meter and the print (and a nice chopstick is always good). If I told you anything wrong you will figure it out.
I'll look at the print again over the weekend if you need more help, or someone else will chime-in.
Good luck, ds
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ss1965    dsbk! You have been a big help!!! plus retired radio guy, and all the other's that have taken time to add a post! I am farther than i was to the source of the problem..
I have all ready replaced to 10 mfd. cap. I had the 470 ohm resistor lose checked both with meter and both were good. The low bias wire gray/violet is attached on the buss where cap & resistor are soldered to it..I resoldered the connection's when I had checked the cap & resistor...so solder joint is o.k. but I am going to have recheck it again....but I must be getting close...( I hope)
I will be looking at it over the weekend...
Steve
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ss1965  Just rechecked the 470 ohm resistor & 10 mfd cap & rehooked jumper to ground still no voltage at the low bias gray/violet wire...the 3.3m R 12 & 18m. R13 resistor's are good...
If I understand schematic there is a green /white wire between the R 12 & R 13 resistor to a closed switch? IF I understood correctly earlier post there should be a switch with closed contact's to make low bias show voltage? Am I correct on this thinking?
---------------  
ss1965   P So far the test button contact's are checking O.K. with continuity meter...a few more to check & then I don't know what to come up with?? :?
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ss1965     One more up date! Contact's on test buttons seem o.k. the 3.3meg & 18 meg resistor's are as shown in schematic...I discovered the two #55 light socket's show continuity between the center contact & socket housing with light bulb's removed! to me that is not very good...any opinion's?
Steve
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dsbk    That's OK. Looking at the print you will see the lamps come off a transformer winding through a 10 ohm pot and 16 ohm resistors. If they are glowing with equal brightness and change when you adjust the pot, you can move on. That circuit is always producing the grid drive signal and you should see it at point EE and to your test1 and test2 switches on normally-open contacts.
You are using your dc scale for the bias readings - right?
Concentrate on what should be switched in and out. Make sure the resistor string from D8/C6 to point EE is complete and correct values. If you lift the bk/wt off of point EE, you can read the entire signal string with your ohm meter if the unit is unplugged and you press test1 or test2. This way you can read ohms from -Vdc source to the point EE conductor. Lifting the end off EE will get the return off of chassis so you can see through the string sequentially resistor-by-resistor if need be.
Check D7 for approx. +16vdc. If you still have problems pull the FET Q1 or replace it and measure again bias. A bad FET could be dragging you down.
No time to look at the print right now - I'm having generator madness service calls this month, and glad to get them.
ds
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dsbk    For internet searches I'll post the conclusion here, which the OP put into a new thread.
The problem was Q1. Tester repaired.
ds

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PostSubject: Re: Tube testers    October 9th 2013, 7:34 pm

I just got my first tube tester I've ever owned. I used to bring my suspect or unknown tubes over to a friends house to use his dad's Mighty Mite, back in the day.
Finally got my own--a Superior Instruments TW-11.
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PostSubject: Re: Tube testers    June 24th 2013, 12:02 pm

Thanks Alan, That is an Awesome Tester!

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