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 Post subject: B&K 747 Tube tester
PostPosted: Mar Sun 21, 2010 3:40 pm 
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Is the 747 a good one ?
Does it compare to the king TV7 ?
I've read that it is a mutual Conductance, not emission type.
Any good or bad points ?

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PostPosted: Mar Sun 21, 2010 4:01 pm 
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The B&K is a nice tester. It's no secret I have a love/love relationship with them, since I own every B&K tube tester ever made. I would tell myslef the benefits over the TV-7 start with size (portability) and weight. Then go onto easier set up, and an established factory calibration procedure. The 0-120 scale still bugs me, but the TV-7 is saddled with that as well.
The only downside to the TV-7 is the 5VAC Grid signal that some low current tubes don't want to see. Other than that, the TV-7 is a great tester as well. I mean, it's a Hickok. The rotary switches make set up a pain sometimes, but if the tube isn't listed on a B&K you're screwed. At least with a TV-7 you can figure out a setting with some trial and error. If the 747 socket isn't wired for that tube, you can't test it (not for gm, anyway). :cry:
Oh, the B&K should be a lot cheaper, so if your wallet is skinny, you should appreciate that aspect.

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PostPosted: Mar Sun 21, 2010 4:51 pm 
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The last three B&K 747 sold for over $300 to $350 + shipping lately on eBay, good luck. So they are popular lately. Tone Lizard list this with many other units and their attributes, pros and cons. If you are working on old radios with 4 pin tubes, no this will not work. For later radios and guitar amps or stereo amps it is fine. They are solid state which is a plus. Here is a secret, tube testers share much of the same circuitry. For the ones that are truly desirable, Hickok and Triplett, the prices have got silly, into the +$1000 range. Are they that much better? Not for me, I just want to check for shorts, gas and how relatively strong it is. There are many good testers, brands and models. Do you have to have a dynamic mutual conductance tester? An emission tester can be had for under $100. It will do most of what you need, thumbs up or down on a tube. I have a dynamic tester, a Mercury 1000, similar to the Mercury 1200. They are excellent (dynamic) testers and similar to the B&K 707 (tube version of the B&K 747), They share basically similar circuits. The problem with my tube tester and the B&K 747, is it always test tubes like a 12AX7 as low, due to lack a variable test signal (as most testers don't have either). You have to get fancy to measure that. Do you care? The manual for the B&K just has a note and says of the 12AX7, 'Tube good if it reads 22 or more'. This is all in this link below. To me getting a tube tester is easy, but learning how they work is fun and educational. They all do similar things but are all compromises, and the tester is dependant on your budget.

www.tone-lizard.com/Tube_Testers.html

"The purpose of the tube tester today is make money for the person selling the tester on eBay." tone-lizard

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PostPosted: Mar Sun 21, 2010 11:06 pm 
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Tone Lizard is Randy's site.

Hi Rand - 'scoin?

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PostPosted: Mar Mon 22, 2010 1:09 am 
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I like the small size of my TV-7 but other than that it seems like an average gm tester. The later B&Ks - 700, 707, 747 are all fine for later radios, TV, and audio. They won't test the tubes from early radios. If you can find a nice one for a good price, get it.

Denis, was it you that was working on an upgrade for the B&K/12AX7 settings?

I found another one of those weird B&K 675 punchcard testers. I wonder if it does anything better than the standard B&K.

-Steve W.


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 Post subject:
PostPosted: Mar Tue 23, 2010 12:00 am 
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Location: Stafford, Texas USA
Adamc

The B&K 747 is a good tester. Does it compare to the king TV7? The TV7 is just the Hickok circuit used by the government to make Tube tester for the military, only the TV7-B was made by Hickok. TV7 King only because of the numbers made and the spending of large amounts of TAX dollars. Each copy of the TV7-D/U is said to have cost over $800.00?.

The B&K 747 can test about 96% of all tubes used in radios and TV’s, by using the programmed sockets no. 22 thru 30 and adapters. The B&K 747 tube tester is easy to make an adapter for.
By making an adapter, using Octal socket 24 on the 747, a tube manual, and Read pages 20 to 23 in the Instruction manual. You can test all most any tube.

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. 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. Set switches 1 to 6 for tube part being connected to. Switches 7 thru 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.
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. So tubes with identical sections can be checked for balance between sections.

jimmie


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 Post subject:
PostPosted: Mar Tue 23, 2010 4:03 am 
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BPlus wrote:
I like the small size of my TV-7 but other than that it seems like an average gm tester. The later B&Ks - 700, 707, 747 are all fine for later radios, TV, and audio. They won't test the tubes from early radios. If you can find a nice one for a good price, get it.

Denis, was it you that was working on an upgrade for the B&K/12AX7 settings?

I found another one of those weird B&K 675 punchcard testers. I wonder if it does anything better than the standard B&K.

-Steve W.


Hi Steve,

I did a mod that optimizes bias and signal for 12AX7 testing. It also requires a meter port for a digital meter since the B&K has not enough meter sensitivity. I used a regulated DC filament supply. It came out beauty. It splits hairs too. That Gm bridge is just amazing!

However after testing hundreds of 12AX7 from many sources with a few kinds of testers, and on my Super 707, I will tell you what you already know - that the corelation between tester Gm reading and what the tube actually does in a normal 400 volt audio circuit stinks. There's no telling if the tube will be stronger or weaker than indicated - a dual-triode could be both!

So I have this precision low-level test that is nice, but still not real.

Now I test them all on the bench at 400 volts in a circuit that will give me 10 vac out with 169.5 mvac in. I call the X59 tester. It don't lie. Chuck helped with some SPICE modeling. The basic circuit came from Amperex as their standard.

The B&K is still used on all tubes to find shorts and such, because it has that great grid-emissions detection circuit, and to test Gm on everything except the 12AX7 types :roll: This tube is sensitive to every parameter.

I wasted allot of time building that Super 707, but boy did I learn allot.

As you said - just test them in the amp!

Thanks for asking, Steve. Hope you are well.

Oh yeah - to be on the thread - the 747 has an improved 12AX7 test over the 700 and 707.

Denis

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Last edited by dsbk on Aug Fri 26, 2011 12:13 pm, edited 1 time in total.

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 Post subject:
PostPosted: Mar Tue 23, 2010 2:33 pm 
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Location: Erie, PA
I used to work on a lot of tube preamps and integrated amps like Dyna, Scott, H/K, etc. And you are right, there is no tube tester that will reliably predict what 12AX or AU7's will sound like in an an amplifier circuit, or the level of distortion they might produce. I always did trial and error with a big box full of them until I found the best sound and balance on whatever I was working on.

Mark


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 Post subject: Re: B&K 747 Tube tester
PostPosted: Aug Fri 26, 2011 2:26 am 
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Joined: Aug Fri 26, 2011 2:21 am
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Hi new here. I know this thread is old but I found it informative.

I'd like to see a schematic of the super 707!

I use a little EMC 213 to test 12ax7 and 12au7 tubes. Gives a nice quick test of quality/shorts and seems to prove it's results in my Fender amps. My 707 does all the rest very well.


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 Post subject: Re: B&K 747 Tube tester
PostPosted: Aug Fri 26, 2011 12:04 pm 
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Location: Norwalk, CT
Welcome aboard bcutter.

Thanks for the interest. The print is not available. I do have several Super 707 units operating in various parts of the world, but the results are just a slightly better illusion.

Build a bench jig, or an actual tester, from the specs in the back of the RCA manual for tube setups, and you will have a real life gain test that correlates to actual performance. It easier than modifying a tester and you can spec gain fast.

You can be the local 12AX7 king!

ds


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