10BP4 without Ion Trap?
 

Will someone please sell me or trade for a double field ion trap assembly suitable for a 10BP4 crt. I have posted before in confusion of what is the right trap. My tube came with a single trap and the brightest raster was with the thing pushed all the way against the tube base. The 1949 set seemed to have had crt work when I got it and a single field trap was just laying on the chassis. It looked as if my troubles are picked up where someone else left off long ago. Someone told me that if I used no trap and got any raster at all that a newer gun had been used on a rebuilt tube that does not reqire ion trap. Well I got a raster without a trap but I am still skeptical. I dont want to ruin a good tube! I know the old manuals call for a double field ion trap and there has to be a reason. I see no evidence of an aluminised screen on my crt which I think is required for tubes with no trap. I feel like I should try a correct trap. Any advice or ion traps will be highly apreciated.:dunno:

There was a guy selling a bucketfull of them recently.
Maybe the buyer would sell you one?

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=3638

Rebuilt or new tubes that have aluminized screen do not need an Ion Trap, tube number with A as a suffix should be the indicator.

Terry, my tube is a 10BP4A. If this means I need no trap than thank you so much. I will now be at ease in continuing to work with the set. This doubt has kept the whole thing at a halt. The set is an RCA 8T-243 circa 1948 and needs a set of knobs if anyone has them. If anyone within reasonable distance of Soutwest VA likes old RCA roundies I would like to trade this set for an early 50s roundie with the more circular looking crt border like the early color sets used, or even better a Zenith Porthole. May even sell straight out. I know these sets are desireable but I must admit that I just dont like the looks of the thing. Being the oldest set in my collection and the only roundie I felt like it deserved some fixing up. I would much rather look at any of my 50s sets. I have posted in regard to a 58 Zenith Space Command that I own. There is a set I plan on setting up for regular use. Nice 24" crt and remote w/beautiful cabinet and great sound. What more could a man ask for? Color maybe?? Naaaa.......

Thanks to all for the helpfull replies!

There were some 243's that had a double D (round) screen. I don't recall if they were the early production or the later.
I have two 243's and they both have the rectangular mask.
If you could find the round mask you could change it!


The 10BP4A should be an aluminized tube.

Just thinking here, someone correct me if i'm wrong...

remove the yoke and all coils and magnets from the neck of the tube, BRIGHTNESS TURNED ALL THE WAY DOWN, turn the set on and slowly bring the brightness up till you can just see the spot, it should be dead center in the screen if it's a straight gun tube.


[QUOTE]Originally posted by Tubejunke
know these sets are desireable but I must admit that I just dont like the looks of the thing.

The reverse is also true, a bent gun tube (non aluminized) will have no picture with magnets removed, only way to get brightness is to use a magnet on the early tubes. My stromberg has no magnet but uses electromagnetic focus, has burn size of silver dollar right in the middle of the tube, when you turn it off it nails the phosphor....

The Dumont 12JP4 is straight gun/non aluminized.

They used a relay to keep the tube off till the sweep circuits were operating and to cut it off when shut down to prevent burning.

Do you have part numbers for the knobs? I have a bunch of NOS RCA knobs, but believe that most are for middle 1950's sets.

I dont have any part #s for the knobs. I have noticed that RCA used the same knobs on their sets for several years. I may be able to find a usefull picture on the net unless someone on this forum knows the part #s. That trick Eric mentioned is a good idea but I think the result is the same as simply removing the trap and turning the set on. If you get a raster at all the trap must not be needed unless there is a possibility of some other magnetic force around the chassis bending the beam to a viewable position. Pretty far fetched I guess. I really wish I could find that double D mask Eric mentioned or even a non broken rectangular unit. Mine fell to the floor and broke in two. This set has been a headache from the get go.

10BP4A used the same gun as 10BP4. The only difference was a faceplate of gray filter glass instead of clear. The 10BP4C and 10BP4D (clear and gray filter respectively) versions were the ones with aluminized screens. Aluminized-screen tubes are easily identifiable by the aluminum coating being visible particularly near the front of the "funnel" at the junction of the faceplate just ahead of the front border of the outer "dag" coating and near the anode connector where the tube was masked to keep the outer "dag" away from the HV terminal. If you see a silvery coating through the glass in these areas, the tube is probably equipped with an aluminized screen (example, 10FP4).

After a lot of consideration I have drawn a conclusion. My tube is a 10BP4A. It is marked that way on the socket. It has not been rebuilt with an alumanized screen and a straight gun. It does need an ion trap, namely a double ion trap and thank God some nice person is going to send me one. Maybe after a year of delay and worry I can move on with this RCA 8T-243. I did try the tube with no trap at all and got a raster of sorts but I still didnt feel right about running the tube more than a few minutes and I think I did the best thing. Once I get the trap I will have to read up on how to set it up. I already know that one magnet is stronger than the other and it matters which faces foreward. I think I have a little more info in one of my older repair books.

This information from RCA service literature should answer your questions:

The tube should be installed with the high voltage connection approximately at the top. The final orientation of the tube will be determined by the position of the ion trap "flags".

Look at the tube gun structure. The second cylinder from the base, inside the glass, is provided with two small L shaped metal flags. The tube must be installed so that when viewed from above the neck, these flags stick out horizontally, parallel to the chassis.

Slide the ion trap magnet assembly over the neck of the tube with the large magnet toward the base of the tube, and with the arrow on the assembly on top of the neck pointed toward the screen. The front magnet is moveable on the assembly, and should be positioned so that the gap is on the left side when viewed from the rear, and even with the gap in the rear magnet. The assembly should now be positioned so that the rear magnet is directly over the "flags" on the gun. (Turn the set on, and set the brightness control fully clockwise and the contrast (picture) control counter-clockwise).

Starting from this position, adjust the assembly by moving it forward or backward, at the same time rotating it SLIGHTLY on the neck for the brightest raster. Reduce the brightness control setting until the raster is slightly above average brightness. Adjust the focus control until the line structure of of the raster is clearly visible. Readjust the ion trap assembly for maximum raster brightness. The final adjustment should be made with the brightness control set at the highest position where good line focus can be maintained.

As for that glowing spot in the center of the CRT screen after power down, some sets had a circuit that had a cap connected from the brightness circuit (feeding the grid 1 of the CRT) to B+. Idea is that when the set is turned off, the B+ will collapse quickly, and the cap will take longer to discharge. This will force the CRT tube into cutoff thus blocking the electrons that would produce the spot. Once this cap is discharged, the cathode will be cold.

Spots on the screen
 

On that last subject, last week I powered up a 12" Philco ('50 model) and after watching for awhile I turned it off, unplugged it and unhooked the cable. 2 hours later I went in the room and still had a spot on the screen. It was actually jumping around, so much so at some times that it made me wonder if vertical deflection was running. Goes to prove, I guess, just how much of a charge can be held in a tv.

Thanks a million to Bill for posting the double trap setup info. I'm certainly going to save and print that. There is plenty of info out there concerning the easy to set up single field traps but I have found none on the double. Great stuff. I'm starting to get excited about my only roundie again with this info and a very nice person who I think is sending me a trap. I really wish I could find a double D screen border. I think they look cooler...