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 Post subject: Short light on B&K 747b don’t work.
PostPosted: Jan Mon 06, 2020 10:25 pm 
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Ok guys I am trying to take the easy way out. I just finished calibrating my B&K 747b tube tester. I changed all capacitors 1st. All went well except for the setting of the short light. I was able to calibrate the grid emissions which is after the short calibration. I can turn R20 all the way both ways and can not get the short light to light. Any thoughts?


Last edited by oldtvsandtoys on Jan Mon 06, 2020 10:55 pm, edited 1 time in total.

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 Post subject: Re: Short light on B&K 747b bong work.
PostPosted: Jan Mon 06, 2020 10:37 pm 
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is the lamp/light good? NE-1 neon lamp

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 Post subject: Re: Short light on B&K 747b bong work.
PostPosted: Jan Mon 06, 2020 10:47 pm 
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for those who want the manual.

http://bama.edebris.com/download/b&k/747(2)/747.pdf

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 Post subject: Re: Short light on B&K 747b bong work.
PostPosted: Jan Mon 06, 2020 10:56 pm 
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Do you have 100 volts on one side of the neon? Is the shorts switch making contact? Is your 1 meg resistor good?
Attachment:
747.jpg
747.jpg [ 194.42 KiB | Viewed 2067 times ]


DM


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 Post subject: Re: Short light on B&K 747b bong work.
PostPosted: Jan Mon 06, 2020 10:57 pm 
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glue_ru wrote:
is the lamp/light good? NE-1 neon lamp


That’s would be a good question, but I have been told it’s rare they go bad.


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 Post subject: Re: Short light on B&K 747b bong work.
PostPosted: Jan Mon 06, 2020 11:00 pm 
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Location: Detroit, michigan
devilsmist wrote:
Do you have 100 volts on one side of the neon? Is the shorts switch making contact? Is your 1 meg resistor good?
Attachment:
747.jpg


DM


Good place to start. I will check in the morning. Thanks


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Mon 06, 2020 11:09 pm 
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cool, check the lamp, check the circuit. We'll be here :)

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Tue 07, 2020 4:52 pm 
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Ok found the problem I need a new NE-1 neon lamp. One wire broke off. Part number 401-002-9-003
Anyone have a new one or used on to sell?


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Tue 07, 2020 7:28 pm 
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I found this: https://www.interlightus.com/light-bulb/NE-1

Still, that's a rare bulb. I might convert that to use a different bulb if it were mine. I found some pictures in another thread here. Is that a bayonet base? Yoy might be able to find an incandescent that will fit.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 1:00 am 
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An incandescent lamp will not work. The circuit depends on the firing voltage of a neon lamp.
There is a possibility that NE-1 is a typo or just refers to the ID in the parts list (like R1, C1).
I think the actual neon lamp numbers start with NE-2 and there are variations of NE -2.
Can you see any marking on the bulb? Sometimes there are letters imprinted in the glass at the pinch were the wires exit.
Glow lamp data.
https://static1.squarespace.com/static/ ... ations.pdf

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 1:14 am 
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How did you determine the neon lamp is defective, you cannot check it with an ohmeter.

DM


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 1:17 am 
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It is the "NE-1 lamp", a thread covering the replacement exists. Does look like a NE-2 with resistor, Sal sells cheap, ad to right
viewtopic.php?f=8&t=205856

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 1:48 am 
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To end all this confusion PM me with your address and I will drop a couple of these bulbs in the mail for you.

DM


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 1:54 am 
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wow, solved, way to go DM !! woo hoo

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 5:11 pm 
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devilsmist may have "solved" the problem but I think some of you are still in the dark.
There are two versions of that B&K tube tester, 747 and 747B. That combined thread glue_ru linked to
confuses the two. The main differences between the two is the pilot light system. The shorts circuit is the same however. The original 747 used a neon lamp and a resistor across the primary of the power transformer, which is the usual set up for a pilot light, it has two neon lamps in total. The 747B has the pilot light as part of the tube filament supply, it serves two purposes, one a power indicator, the other is filament current draw. That pilot lamp is a low voltage incandescent and is driven by a transistor circuit that indicates that the tube filament is drawing current.
The original 747 has a fuse inside on the filament circuit. The 747B has a circuit breaker on the panel for the filament circuit.
Neon lamps, incandescents and LEDs have very different electrical characteristics.
https://www.giangrandi.org/electronics/neon/neon.shtml

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 10:54 pm 
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ugh

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Last edited by glue_ru on Jan Wed 08, 2020 11:10 pm, edited 1 time in total.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 11:06 pm 
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Joined: Jun Thu 12, 2008 1:05 am
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Location: Detroit, michigan
devilsmist wrote:
How did you determine the neon lamp is defective, you cannot check it with an ohmeter.

DM

When checking r20 I looked at the bulb and could see a broken wire on the bulb. The wire broke at the glass so I can’t fix it.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 11:12 pm 
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Location: Detroit, michigan
glue_ru wrote:
I don't believe it is solved that easily or by someone barging into every thread acting like THE expert, not buying DM's BS

DM didn’t solve the problem, I found the broken wire when I was checking other parts of the circuit. All DM did was offer me a new bulb and I thank him for that.
Let’s all just get along and not turn this into Videokarma.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Wed 08, 2020 11:24 pm 
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glue_ru wrote:
It is the "NE-1 lamp", a thread covering the replacement exists. Does look like a NE-2 with resistor, Sal sells cheap, ad to right
https://www.antiqueradios.com/forums/vi ... 8&t=205856

Ok who is Sal?


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Thu 09, 2020 12:24 am 
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Location: Dallas, TX
I believe he means "Sal's Capacitor Corner" which advertises on the right border of the pages here.
He is selling NE-2 lamps with and without resistors. Less than a dollar.
I just wanted to point out that neon bulbs may not being as simple as they look.
It is possible that a standard NE-2 will work. You could try it and see if the adjustment range of the
calibration pot will let it work OK.
With an application like a pilot lamp across the 120 VAC line the breakdown (firing) is not very critical,
the voltage present is way over the breakdown just about any of the neon lamps.
With a tester circuit like in this tester (very similar to any tube tester shorts circuit) the voltage might be more special.
If you can't see any markings on the bulb, I could open up my 747 and see if I can tell what it might be.

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