Testing a 15GP22
 

Does anyone have any tips on testing a 15GP22? I have a Sencore CR70 I haven’t used before and a bk 465. Any tips or specific things I should do would greatly be appreciated!

Might want to confirm the sencor is good on a more common tube first... if for example your heater supply or its control is not.working right you could end up putting 12v into a 6v heater and damaging a rare CRT.

If the 465 is known good and assuming use of a universal adapter and similarly to my 466 testing is straight forward. Check pinout of the tube in datasheet and socket wiring if it is installed in a set to be confident in set up before powering up the tester. Start at 6.3v for the heater use the same settings you would for a 10bp4 and give it plenty of time to reach proper emission levels. If the CRT is asleep it may take in the neighborhood of an hour to wake up at 6.3v....best not.up the heater voltage till you've given it plenty of time to wake up...if it has taken over an hour and it has not climbed into the good range you can up the heater voltage to as much as 1.4x the normal value and let it sit some more. If after hours of gentle wake up it is still not good try the mildest rejuve the cr70 can do, and work your way up some if needed. If the cutoff test acts wierd your tube may be too gassy to use.

The Sencore will work fine. Dave Pike and I did the final test of a 15GP22 I had, and subsequently sold, on a Sencore CR-70.

Note however, that a Sencore will only tell part of the picture. It is technically possible, but very unlikely, to have a tube that tests good on the Sencore, with a good, normal cutoff response, that is too gassy to use.

First test the tube for emission, allowing time for it to wake up as Tom alluded to.

Then, test cutoff. This is critical. If turning the cutoff control moderates the cathode current normally, you have a good tube. If the tube responds normally until you reach a certain grid voltage, and then all of a sudden cathode current runs away uncontrollably, the tube is gassy.

Also look in the neck of the tube while checking. A faint blue glow on the inside surface of the neck glass is possible, and actually a good sign. (In very high vacuums, the surface of glass is actually slightly conductive. This is why some 6L6s, 6W6s, 6Y6s, 6V6s, etc have graphite coatings in them... it's there to collect stray electrons that would otherwise light up the inside of the glass slightly.)

A purple, pink, or indigo glow BETWEEN elements of the gun assembly is bad and a sure sign your tube is too gassy to use. Getters are also sometimes indicative, but can not be relied upon. Anything white is clearly a gassy dud. Good looking getters could be a good or bad tube. Faint looking getters, even nearly invisible to the naked eye, are often a bad sign, but aren't necessarily so. I've seen one 21AXP22 with NO visible getter material produce gorgeous color pictures over the past 5 years, so it's possible.

The best check of gas is a nice, strong tesla coil. They can be purchased or built for reasonable cost. A gassy 15GP22 will light up like a Geissler tube...

I took off the purity ring and shield and cleaned off the crt neck. The getters look shiny still, so I guess it’s still under vacuum?

They look pretty rough (and white) around the edges. Assume the tube is bad until further testing proves otherwise...

My gut says the tube is a leaker.

I concur with Ben. The getter on that tube is what you would expect it to look like if it was a gasser. Later tubes that I have seen, which were likely rebuilds done at RCA, have had HUGE getters. The getter on this tube is indicitive of those found in the initial production runs. All those getters were very small, almost insignificant little getters. I will never understand why they used such tiny little getters for such a large tube volume, because as later examples have shown, there was plenty of room to flash a much larger getter in the same location.

I currently have a NOS RCA rebuilt tube for a Westinghouse chassis that I am working on for a client. It has a production date in the early 1960's. The getter flashes on that NOS rebuild tube are about the size of a silver dollar. I also have a gassy tube with the same large getters, so the size of the getters is no guarantee that the tube is good. This proves that even after RCA rebuilt a worn out low emission tube that was known to be under vacuum, the process of rebuilding the previously "under vacuum" tube could cause the newly rebuilt tube to spring a leak where there was no leak before.

I have seen only a small number of 15Gs with these huge getter flashes. But of those tubes with the large getter flashes, I have only seen one that was gassy. It seems the original early production 15Gs with the tiny little getter flashes have a higher failure rate. It is possible by the time RCA started rebuilding 15G's, maybe they had revised their production process so that they had a better probability if producing a rebuilt tube with large getters that would hold vacuum.

Too bad we will never know the real truth about what RCA may have done in late production rebuild tubes to increase the reliability of those bottles.

I've had two good 15GP22s pass through my hands with unusually large getters, consistent with Bob's observations. A dud that had a pair of small type getters where normal early 15GP22s just had one, for six total as opposed to three.

A second one that had the extremely large "silver dollar" getters Bob referred to.

One had a small label marking it as a circa 1960 rebuild, the other had an extremely obvious and poorly done neck weld, so I assume that it too was likely a late 50s or early 60s rebuild.

Well it sounds like I’ll be waiting for the etf to ramp up their crt rebuilding production then....

Inquiring minds would like to know... what set? CT-100, 15 inch Westy? Something even more interesting?

It ain't over till the fat lady sings... throw a tester on it and see what it does... I've seen monochrome metal cone CRTs with whiteish ghosts of getters make a decent picture...

If it is a ct100 you could bring it here and I could slide my working chassis into your cabinet and check it the surest way.... with a working chassis.

Tom, thanks for offering to do that, but I don’t live that close to you! I have a sencore cr70, but the universal adaptor hook kinda confuses me. Unless I hooked it up wrong on a 10BP4, it didn’t seem to work. I need to try it again. I also have a bk 465, but need help on how to use that on this crt.

If your 465 is like my 466 then the main connector on the end of the CRT cable is a 10BP4 style socket...That socket plugs right onto those 10BP4s without an adapter. Mine did not come with a universal adapter so I made my own the lazy way: I took the base off a defunct oscilloscope CRT (same base as a 10BP4 but with all the pins populated, but of course the base from a dud CRT would also work) soldered leads into the red/monochrome gun and heater pins and made my own single gun universal adapter (I may expand it out to three guns someday). You can use the 10BP4 pinout or an existing adapter and ohms/beep mode of a DMM to figure out pinout of the adapter base. I color coded my wires and added some alligator clips to the ends and it workes fine anywhere I don't have an adapter but know enough about the CRT.
All you really need for the 466 to test a CRT gun is the heater leads, Cathode, G1 and G2. All the other pins of the CRT (like focus) are not really functionally connected.

Make sure your switch settings are as stated below whenever using the universal adapter.

https://c2.staticflickr.com/2/1922/4...6b6ebce1_b.jpg

On my bk 465, the socket for the 10bp4 socketbis part of a multi socket adapter. I will use the socket from a crt brightner to make this test socket. What pins should there be leads to it and do you have pictures of yours Tom? Kevin, thanks for that link to the sencore, I will double check my settings and try it again.

Kevin, I did everything the manual said and my 10bp4 that I know is good didn’t light up. Something must be wrong with the tester. So I’ll have to make the adapter Tom mentioned.

The CBS-Hytron picture tubes from same era also had a metal bell, did they hold vacuum better?

Meanwhile, the CBS Colortron was all-glass!
..as was Dr Ernest Lawrence's Chromatron!

The socket on mine is both the 10BP4 socket and the receptacle for the adapters the red gun and monochrome gun are the same switch setting on the gun select switch on mine. They mapped the monochrome gun socket pins to an additional set of pins I used at least one pin of that additional set in my adapter...Since it sounds like the 465 uses a different socket on the end of its main cord my exact pin map probably won't work for you...Never the less here is what I made to give you a general idea of what you want to make.

https://farm5.staticflickr.com/4917/...98a1ca14_z.jpg https://farm5.staticflickr.com/4906/...c4b9e98a_z.jpg https://farm2.staticflickr.com/1955/...4f670d69_z.jpg https://farm2.staticflickr.com/1936/...cdb1ed6c_z.jpg https://farm5.staticflickr.com/4805/...7128fb2c_z.jpg

A 10BP4 has the exact same amount of populated pins as your tester needs to test a tube. https://www.radiomuseum.org/tubes/tube_10bp4.html
You need the two heater pins (1 and 12) on either side of the key on the bakelite center locator 'pin', Cathode pin 11, G1 pin2, and G2 pin 10...
Those wires are color coded on any normal color CRT harness as heater (Brown or sometimes black), Cathode (yellow with stripe the same color (R,G,or B) as the gun being driven), G1 (solid color the same color as the gun being driven), and G2 (White with stripe the same color as gun being driven).

I color coded my leads to match a standard color CRT harness (with only a red gun) then added tags to the leads so I would be certain to remember what each lead is meant to go to. I actually used that crude adaptor to test my 15GP22. I had to switch off twice and swap the Cathode(K), G1 and G2 leads to the other color guns but it did the job fine.

PS: Sorry for the slow reply I've been in swapmeet mode since ~noon yesterday.

Did Flickr Go Ransom?
 

Tom............Your last photos did not share with me. Why was that?

Flickr plans to delete or ransom photos from free account s with more than 1k images.... I was at 1400 plus so I had to delete over 400 to meet their limit.... most of it was things I've sold but I had to break a few less important pics to...

I now need to delete stuff from Photobucket to make room, create a new Flickr account, or go shopping for a new free image host....:thumbsdn:

I made the adapter and crossed my fingers...

The first was the red gun. The next two are the blue then green guns!

Can you get a better photo of the neck? I see some pink, which would ordinarily be game over, but it looks like it may just be marker on the neck glass...

That pinkish red line is the line for where to set the purity ring at the back of the neck. Is that what you’re talking about?

I took the purity tube off to get better pictures of the neck...

Envy!

That blue glow I see between gun elements in the most recent pics and the seemingly abnormally bright heater glow are both very worrisome. The two unusably gassy round CRTs I have (21AXP22 and a 21FJP22) both do that when tested.

If you can get it to produce a raster in that state, run it as much as you can while it lasts to try to excite the gas molecules into hitting the getter.

Well it doesn’t seem like there’s a real definitive way to know other than to restore the chassis and see what happens...

I'm confident the tube is too gassy to use in its present state. The gassy 15GP22 I tested in a CT-100 here in the Detroit area also has that tell tale blue glow between the gun elements. Sometimes the voltage of the tester itself is enough to strike the gas and get discharge like that.

Reread my earlier post: blue glow on the inner surface of glass = harmless.

Blue glow BETWEEN elements = bad.

The blue glow would tend to suggest the gas is either argon, nitrogen, or oxygen. Nitrogen or oxygen could be cleaned up by the getter, argon, no. It just won't bind to the barium.

Well I guess I’ll just wait for the etf to rebuild this crt. Is there any progress there with it becoming reality?

I've never owned a 15GP22, but it would seem that either way you don't have too much to loose by recaping the set and give it a whirl.