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?ViewItem&item=2219132272&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.

Originally posted by dewickt
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....

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.

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...

Originally posted by jshorva65
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).
1. The 10BP4 and 10BP4-A require a double field ion trap.

2. The 10BP4-C and 10BP4-D require a SINGLE FIELD ion trap, even though they are aluminized.

3. There is no telling what a rebuilder might have done, but if straight guns were used for rebuilding, they most likely would have been used on the C and D versions, since these already had aluminized screens. Rebuilders usually do not replace the phosphor screen, so the A and B versions should have been rebuilt with bent guns requiring an ion trap (unless the screen was replaced, but this would make it a C or D version).
:dunno:

Wow! More great information on this lost subject. I am so glad I set this project to the side instead of believing my tube needed no trap at all. No telling what damage I would have done trying to operate this set with a single field trap or no trap at all. Yes my set produces a non linear raster with no trap. I take it that the rule of thumb about no ion trap no raster does not apply to the less common double field requirement. I hope my trap gets here soon. Any thoughts on getting a double d screen border anyone?

RCA 8T-243

Tubejunke,

Were you able to see the "flags" on the gun in your tube?

If by "flags" you mean the small metal rods that stick out of the cylinder (2 on each side) that mount it to the glass electron gun support than yes I see them. There is nothing else connected to the second cylinder. With the gun supports paralell to the chassis my HV connection will not be 12:00 but more lile 2:30. I have not got a trap yet so I am still at a standstill and working on that God awfull 58 Zenith Space Command that I have posted plenty about. Just dropped another $10 in that catastrophe. I wanted the correct 5au4 instead of 5u4. Still the same set I carried through the door. I kind of got stuck into basically a complete rebuild of this set chasing problem components with an ohm meter. By now I would have come out cheaper sending the thing to a shop and having the original problems tracked down and then brought it home and replaced things. Something on this set is above my knowledge base I guess. Maybe some transformer or disc cap. Who knows?:dunno:

Here's a little sumpthin sumpthin that y'all may find interesting: D'OH! (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3638&item=3287301821)

Anthony

Anthony, are you sure you are on the right topic? That is cool if you have NOS crts. Do you sell them? We have been talking about the lost art of the double field ion trap magnets and 10BP4 tubes and variations of the type. Is that a 10BP4 in the box. You mentioned Christmas early. You can send it to me if you want. As long as its not newer than 1966. Tell us what it is......:dunno:

Nah, I don't have that bottle.....click on the "D'OH!" link above and you'll see what I'm talking about.....plus you'll smack yourself in the forehead and exclaim loudly D'OH!!!

Anthony

Looks like Tony D is the current high bidder on that 10BP4. I bought the 721TS that's currently in my display room from him and I'm extremely pleased with it. I thought I was hallucinating when I won that auction for a fully-recapped set with an excellent 10BP4 with a bid of only $200. The only peculiarity with that set is that the vertical hold takes longer to stabilize at warm-up than I expected, but after warm-up it's rock solid. Considering that the winning bid for the recapped 721TS I sold on eBay in '02 was over $1,000 I almost felt like I'd stolen that 721 at $200. The CRT in the one I sold 2 years ago was "pretty good for its age" but not "like new" although it produced an amazing picture. I had some serious bench hours in optimizing the alignment on that one.

Once I find time for a "break" to work on my own stuff, I'll check out why the picture rolls for about 2 minutes after it first appears on that set and probably take the time to optimize the IF response.

At the moment, I've just uncrated a Motorola 19CT1 with the factory 21" upgrade that was shipped here for a full recap. That one will keep me busy until the Dumont RA-104 gets here for its turn on the bench, then there's an RCA CTC5 scheduled after that.

Yep! Your right. Smack... D'oh... Brain fart...