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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Thu 09, 2020 1:52 am 
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The lamps have been shipped, they are NE-5AC which is a step up from the ordinary NE-2. They come already burned in and sorted to fire a a specified voltage, these were designed for voltage regulation. These are what I always used for tube testers in the repair shop.

DM


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Thu 09, 2020 3:02 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Sounds like that might work devilsmist.
I did take a look at my tester and I can't see any marking on the bulb. The bulb measure a bit under 3/4 inch long and 0.225 inch in diameter. I think the standard NE-2 is longer at about 1 to 1 1/4 inch, which might mean it might not be as visible in this end-on application.
Just to see what I could figure out from the circuit i did a bit of reverse engineering.
I had made a note some time ago that the voltage on C-7 was about 100VDC. From C-7 the circuit goes through R-19, a 68K, then the parallel combination of NE-1 and 2M pot R-20, then to the tube elements through the switching. For calibration you put a 1M resistor to ground in effect. So if R-20 was at midpoint (1M) the neon lamp will see 50VDC (or so) when it should fire, because of the voltage division. If R-20 is at it's maximum (2M) the voltage across the lamp could be 66VDC. So it seems to me the firing voltage needs to be less than 66 VDC and would be best if it was near 50 VDC in order to allow for parts variation over time.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Thu 09, 2020 3:33 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 1214
I don't know of any neon bulbs with such a low firing voltage. I think nearly all of them fire at around 90V unless they are a special type. Once lit, they maintain about 67V if I remember correctly.

I have a book called the GE Glow Lamp Manual, I think. It may expound on this. Or maybe it's from Signalite.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Fri 10, 2020 2:37 am 
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Location: Dallas, TX
bob91343 wrote:
I don't know of any neon bulbs with such a low firing voltage. I think nearly all of them fire at around 90V unless they are a special type. Once lit, they maintain about 67V if I remember correctly.

I have a book called the GE Glow Lamp Manual, I think. It may expound on this. Or maybe it's from Signalite.

That was kind of the point, it might use a special type. Did you read the info that I linked to?
One of those links shows GE data on special neon lamps. There is a lot of variation possible for a given type, maybe they used selected ones of a given type.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Thu 16, 2020 4:37 pm 
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Joined: Jun Thu 12, 2008 1:05 am
Posts: 152
Location: Detroit, michigan
Ok looking on line to find a NE-1 neon bulb I found this. On the parts list for a bk 747 they have NE-1 B&K part # 401-002-9-003
then under the b&k 1077 tester they have NE-2 with B&K part # 401-002-9-003
two bulbs with the same part number?


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Fri 17, 2020 2:28 am 
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Location: Dallas, TX
I think you missed a point I made in a post a while back in this thread.
It is a shame your picture of the parts list doesn't show the column to the left where it calls out NE-1,
because right below that line it calls out the (OFF-ON-INDICATOR) as being a PL-1, neon bulb w/100K resistor.
PL-1 is not a part type, E-2 is not a part type, NE-1 is not a part type either. Those identify the parts on the schematic.

Please note again that you have a 747B not the original 747 model which belongs to the parts list in your picture. The 747B has a 2V-60ma lamp for PL-1 which is a (OVERLOAD-INDICATOR), that model has a circuit breaker in the filament circuit whereas the 747 has a fuse.
Those things happen to be the main differences between the two models.

The good news maybe that the neon bulb in both models (as well as the 1077) looks to be a NE-2,
although in the shorts circuit it might be one selected to have a low firing voltage.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Fri 17, 2020 6:18 am 
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Joined: Jun Thu 12, 2008 1:05 am
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Location: Detroit, michigan
Yes I agree with you. E-2 and NE-1 are schematic symbols PL-1 too. I know neon bulbs fire at different voltages and current.
With that said the b & K 1077 does list the E-2 (schematic symbol) as a NE-2 as both have the same b&k part number 401-002-9-003 and NE-2 is a part number for a neon bulb, I think I will try a NE-2 to see if it works. I will let you know. Thanks for your help


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Fri 17, 2020 6:44 am 
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Joined: Jan Tue 10, 2012 8:39 am
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Neon lamps fail with age. The atmosphere infiltrates the charge space and causes an increase in striking voltage. The only cure is a new lamp.

Neon lamps generally strike at about 90V and maintain at 67V more or less. The main differences among the various types, beyond the obvious dimensional and connection variations, is electrode length, which determines the current the lamp draws. There are also versions with radioactive content to mitigate the increase in striking voltage with prolonged darkness. In some cases there is a wire added on the outside of the lamp for this purpose.

For other voltages, other gases than neon are used.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sat 18, 2020 12:12 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
I could be that a regular run of the mill NE-2 will work. Won't hurt to try it. If you can get it to calibrate correctly problem solved.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sat 18, 2020 12:30 am 
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Joined: Jun Thu 12, 2008 1:05 am
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Location: Detroit, michigan
Notimetolooz wrote:
I could be that a regular run of the mill NE-2 will work. Won't hurt to try it. If you can get it to calibrate correctly problem solved.

You don’t think it’s a NE-2?


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sat 18, 2020 2:09 am 
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Joined: Jun Sat 15, 2019 7:43 pm
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Didn't you install the neons I sent you??
The NE-5AC or also known as NE-68, are actually a "premium" NE2. They are already burned in so you don't have to go back and readjust the circuit as the neon ages, they are also treated with a radioactive material so they have a more consistent striking voltage. I have used these these in hundreds of tube testers and other pieces of test equipment over the years.

DM


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sat 18, 2020 2:20 am 
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Joined: Jun Thu 12, 2008 1:05 am
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Location: Detroit, michigan
devilsmist wrote:
Didn't you install the neons I sent you??
The NE-5AC or also known as NE-68, are actually a "premium" NE2. They are already burned in so you don't have to go back and readjust the circuit as the neon ages, they are also treated with a radioactive material so they have a more consistent striking voltage. I have used these these in hundreds of tube testers and other pieces of test equipment over the years.

DM

Going to try it in the morning. One bulb was broken the other looks ok. Thanks


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sat 18, 2020 3:11 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
oldtvsandtoys wrote:
Notimetolooz wrote:
I could be that a regular run of the mill NE-2 will work. Won't hurt to try it. If you can get it to calibrate correctly problem solved.

You don’t think it’s a NE-2?

That isn't what I meant. It is just that my analysis of the circuit pointed to a lamp with a lower breakdown voltage than a regular NE-2, but I might be off. The proof is in the pudding, so to speak.
If a NE-2 gets you to a successful calibration , it works.

Just to beat the horse some more, here is more info on neon lamps. Together with the other links we can all be experts on the subject.
https://www.tiffe.de/roehren/neon.pdf

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sun 19, 2020 4:54 pm 
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Joined: Jun Thu 12, 2008 1:05 am
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Location: Detroit, michigan
devilsmist wrote:
Didn't you install the neons I sent you??
The NE-5AC or also known as NE-68, are actually a "premium" NE2. They are already burned in so you don't have to go back and readjust the circuit as the neon ages, they are also treated with a radioactive material so they have a more consistent striking voltage. I have used these these in hundreds of tube testers and other pieces of test equipment over the years.

DM



Ok Good news and bad news the 5AC or also known as NE-68 I got to work fine. The bad news the tip is longer and sits further back. Very hard to see. Are all the tips on these bulb this long?
On a side note I could not get the NE-2 to fire.


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Jan Sun 19, 2020 8:24 pm 
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Location: Dallas, TX
It always somethin'.
One of the pdfs I linked to show the data for a NE-68 including the part outline.
Looks like they all come with the random tip. You might come up with some way of making the light more visible, maybe paint the sides of the plastic holder white, or line it with aluminum foil.

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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Apr Thu 02, 2020 3:02 am 
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Joined: Jun Thu 12, 2008 1:05 am
Posts: 152
Location: Detroit, michigan
Ok just a update. I have tried the neon bulbs that were sent to me. They would calibrate just fine. But would test all tubes as shorted. I gave up and bought a junk 747
and took the neon bulb. Put it in my 747 and it now works fine. My question is why would the others calibrate just fine but show all tubes shorted


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 Post subject: Re: Short light on B&K 747b don’t work.
PostPosted: Apr Thu 02, 2020 4:15 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
oldtvsandtoys wrote:
Ok just a update. I have tried the neon bulbs that were sent to me. They would calibrate just fine. But would test all tubes as shorted. I gave up and bought a junk 747
and took the neon bulb. Put it in my 747 and it now works fine. My question is why would the others calibrate just fine but show all tubes shorted

I am at a loss to explain that. Glad you found a solution though. I guess the originals are even more special than I thought.

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