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 Post subject: 7JP4 question
PostPosted: May Sat 05, 2018 7:21 pm 
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Location: Madison, wisconsin 53718
I have this 7JP4 that I got with a Batch of NOS Tubes from an Engineer who passed away, I have had this in a closet since last November and am afraid of it getting broken so it has to go.
this Tube is not but maybe new, but was in a box of various CRT's that came with the Tube lot.
I modified an old Tube Scope that used a 5UP1 CRT so that I could drive this Tube shown, the HV Driving it is only like 1.5 kv, and not close to what the rated Voltages are for the 7JP4.
I did this to make sure there were no Ion Burns and to see actual brightness, and to find out if its a healthy tube for someone to use, I will never use it, so I placed it on CL for sale locally
because I don't want to ship as I know the Gun supports can break.

so my question is for you who know this Tube and based on my pictures and test do you think it would be a decent tube?
I just want to make sure the new owner does not have buyers remorse,
or sour feelings against me, this is most important.
it test Excellent on both CR-70 and CR-7000 testers
I know a true test is at full rated voltage but i only have a admiral that i converted to a scope clock years ago and dont want to tear it apart for testing this.
would you says its going to be a decent Tube?
I am Recovering from a Root Canal right now so hope I am not confusing :(

Thanks
Terry


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Last edited by wiseguy on Jul Fri 26, 2019 11:08 pm, edited 2 times in total.
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 Post subject: Re: 7JP4 question
PostPosted: May Sat 05, 2018 10:41 pm 
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Location: Montvale NJ, 07645
Looks like a good tube to me.
The only test I give these is a set test, and this looks like it would pass that no problem.

Too bad you won't ship as I would take it off your hands.


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 Post subject: Re: 7JP4 question
PostPosted: May Sun 06, 2018 12:45 am 
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If it NOS there should be no ion burns, so your good to go.


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 Post subject: Re: 7JP4 question
PostPosted: May Tue 08, 2018 9:49 am 
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Location: British Columbia
From what many have said a CRT tester is pretty close to useless in testing an electrostatic CRT, even a well worn one will test with good emissions, the only way to test one is by trying it in a working piece of equipment like an old scope or something. I believe that they can be shipped, if packed correctly, people have vintage TVs like Motorola VT-71s shipped with the tubes in place so they can't be that fragile. They used to have special cartons for packing CRTs, they had a sort of cradle on the inside constructed in the form of an X where the bell would rest on the X portion and the neck would slip down between. Local pickup is always the safest of course, but shipping can be done, I would use the bus if possible, and don't even think about UPS.
Regards
Arran


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 Post subject: Re: 7JP4 question
PostPosted: May Tue 08, 2018 1:44 pm 
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After experiencing a couple of broken necks in shipping CRTs, I developed this method in shipping my CRTs and I've never had one break using the below method. I've been wanting to make a YouTube video of this procedure, just haven't had the excess time to do so.

1) I wrapped the entire CRT in cellophane (the good kind)

2) Purchase or make a box a little bigger than the CRT

3) place a few foam pellets on the bottom of the box where the screen will rest

4) Spray foam (3 large cans for a 12LP4) around the pellets and place CRT screen on the foam and pellets. Then continue spraying foam around the entire CRT in the box with copious amounts around the neck ensuring a tight fit and tape the box shut, wait over night

5) Trim excess foam from the box seams

6) Double box with foam pellets


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 Post subject: Re: 7JP4 question
PostPosted: May Wed 09, 2018 1:55 am 
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Location: Belrose, NSW, Australia
Instead of wrapping the CRT in cello and having to cut the foam to get the CRT out, consider this method which we have used in my business to ship large numbers of pieces of delicate equipment forward and back.

1. Get a box about 50% bigger all around than the CRT (or other delicate item).
2. Get 2 plastic garbage (trash) bin liner bags
3. Fill one with a suitable qty. of foam and put into the box.
4. Place the CRT onto the foam before it sets to make a nest.
5. Let the nest set.
6. Place CRT in the nest.
7. Fill 2nd bag with foam and place over the CRT.
8. Close the box.
9. Let the top foam in the bag expand and set, making a tight fit in the box.

You now have a reusable packing box with custom made foam fillers. Urethane foam is a very effective shock absorber.

Foam chips in my experience (very extensive) wiggle out of the way in transit allowing the object to contact the box directly - not good.

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 Post subject: Re: 7JP4 question
PostPosted: May Wed 09, 2018 3:29 am 
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Joined: Sep Fri 07, 2007 2:27 am
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Location: Grand Chute, Wisconsin
Or you could avoid shipping altogether by pricing it for sale, pickup only, and let one of the many Wisconsin TV collectors purchase it.

Place it on the VideoKarma classifieds, or the ARF classifieds.

.


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 Post subject: Re: 7JP4 question
PostPosted: May Wed 09, 2018 5:43 pm 
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irob2345 wrote:
Instead of wrapping the CRT in cello and having to cut the foam to get the CRT out, consider this method which we have used in my business to ship large numbers of pieces of delicate equipment forward and back.

1. Get a box about 50% bigger all around than the CRT (or other delicate item).
2. Get 2 plastic garbage (trash) bin liner bags
3. Fill one with a suitable qty. of foam and put into the box.
4. Place the CRT onto the foam before it sets to make a nest.
5. Let the nest set.
6. Place CRT in the nest.
7. Fill 2nd bag with foam and place over the CRT.
8. Close the box.
9. Let the top foam in the bag expand and set, making a tight fit in the box.

You now have a reusable packing box with custom made foam fillers. Urethane foam is a very effective shock absorber.

Foam chips in my experience (very extensive) wiggle out of the way in transit allowing the object to contact the box directly - not good.


I really like this procedure much better.....Removing the foam from the cellophane can be quite messy too.


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 Post subject: Re: 7JP4 question
PostPosted: May Wed 09, 2018 7:26 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 270
Location: Madison, wisconsin 53718
LOL
I just wanted to know thoughts on the image produced with the old tube Oscilloscope I hacked into to Drive this tube


Terry


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 Post subject: Re: 7JP4 question
PostPosted: May Thu 10, 2018 1:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: dayton oh usa
scopes use lower hv than a tv.
that looks like a good crt to me too.
last 7jp4 i shipped to a friend was loosely bubblewrapped and double boxed.
the idea is to dampen any impact.
the bubblewrap becomes a spring and absorbs impacts.
its a greater challenge to ship a 21fjp22 without a real crt carton.


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 Post subject: Re: 7JP4 question
PostPosted: May Fri 11, 2018 3:54 pm 
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Location: Seattle, WA, USA
As to the question of testing 7JP4 and similar tubes, there seems to be quite a lot of debate on the subject and I have never encountered a satisfactory explanation of why they go bad. Generally, there are two camps:

Bad Cathode (low emission):
Pros: This is how most other CRTs fail and would explain uniform loss of brightness.
Cons: Multiple people have reported dim 7JP4s that test good on CRT testers. I personally have not seen this when using a Sencore CR-70 or CR-7000, but despite my handle, I actually have not owned or tested many 7JP4s.

Ion Burned screen:
Pros: This would explain tubes with good emission and poor brightness. Also, 7JP4s are not aluminized and don't use an ion trap so they should be prone to ion burn.
Cons: Most weak 7JP4s (that I have seen anyway) are uniformly dim. If the cause was ion burn I would expect the center of the screen to be darker than the edges.

In any case, you have verified emission and reasonable screen brightness so I am pretty sure you are in the clear on this one.

-Matthew

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 Post subject: Re: 7JP4 question
PostPosted: May Fri 11, 2018 5:09 pm 
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Location: Ann Arbor, MI
7jp4-guy wrote:
Cons: Most weak 7JP4s (that I have seen anyway) are uniformly dim. If the cause was ion burn I would expect the center of the screen to be darker than the edges.

With magnetic deflection the electrons deflect more easily than the ions. So the ions hit a smaller diameter section of the screen. With electrostatic deflection, could the ions deflect the same amount as the electrons? If so then an ion burn would cover the whole screen.

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 Post subject: Re: 7JP4 question
PostPosted: May Fri 11, 2018 5:52 pm 
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Location: Chicago, IL USA
Yes, it's my understanding that the ions are deflected along with the electrons resulting in uniform screen bombardment.


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 Post subject: Re: 7JP4 question
PostPosted: May Sat 12, 2018 11:32 am 
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Location: Madison, wisconsin 53718
bandersen wrote:
Yes, it's my understanding that the ions are deflected along with the electrons resulting in uniform screen bombardment.


Thank you all, we will see what happens :)


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 Post subject: Re: 7JP4 question
PostPosted: May Tue 15, 2018 4:05 am 
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Location: Seattle, WA, USA
It is true that the ions will be deflected as much as the electrons. (If you are curious there is an excellent derivation at https://circuitglobe.com/electrostatic- ... n-crt.html). However since 7JP4s were mostly used in sets with masks where the picture would not cover the entire face of the tube, if the problem really is ion burn I would expect the far edges of the tube to be much brighter than the rest.

-Matthew D'Asaro

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 Post subject: Re: 7JP4 question
PostPosted: May Tue 15, 2018 11:05 am 
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Location: Madison, wisconsin 53718
the sharp bright edges on this tube shown above Follows the image when centered or amplitude was changed, from the scope trace and retrace, I was at one point setting my function generator to 12KHZ there was no brightness changes on the far edges, just the trace.
I had seen some of these Tube get a round half dollar sized burn in the center, but I did not see that on this one
below is an example of some that I have seen, if you look close you can see it in the center
I could not find any burns like the one in the picture below ( pic is not from my Tube )


Terry


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