B&K 440 Tester and 5AXP4 CRT woes

Two of my trusty repair bench tools have developed problems. Let's take a closer look.

[@jazbell7]

CRTs had a long run from the Crookes tube of 1897 to the last xxxxP22 color tube of early 2000s. Lots of enhancements along the way, ion traps, metal cones, aluminized phosphor coatings, shadow masks, rare earth metal phosphors, Trinitron. It will be a long time winding down...

[@mikefinn2101]

Bob hope you figure it out sad to see the old tube fail. Thanks for sharing. Mike

[@12345678989814]

It's crazy that little round test CRT that you have I've got one sitting here somewhere that I got when I bought a bunch of stuff from an old TV shop

[@69Dartman]

I have a few crt testors but my favorite is the Beltron that I saw my buddy use back in the day. He told me how to use it and eventually I was given one from a TV shop and I made it work. Later I got a completely rebuilt and updated one on ebay for like 20 shipped. I had to redo some wiring but it wors great and had all the sockets and adapters. I think the last crt I did was a 36 trinitron and it worked well for a short time but they never like being rejuvenated or cleaned. Haven't used any of them in years but they certainly upped the amount of sets i could get running.

[@1McMurdoSilver]

Thanks Bob.. The 8XP4 is the small rect CRT taken out of the box..

[@ElectroRestore]

So sad to hear your test CRT has failed. Hopefully, another one comes along down the pipe soon. As always, enjoyed the video even though it was on a sad note. Glad you did get the tester working though. One prized diagnostic tool going south is enough of a hit to the heart!

[@videolabguy]

I've got two 5AXP4s available. One with the yoke kit in the wooden case. The other is just the CRT. Both are tested good in my 5AXP4 project (part 2) . See my web site for the video and electronics projects and contact info, link is on my YT home page.

[@300poundbassman]

My dad had that VTVM IN your catalogue swiveled. .

[@kevkabluebird1032]

Uh, 75 bucks would be around 760 USD today :D

[@SeekingTheLoveThatGodMeans7648]

I hope you get your CRT tester fixed ok. P.S. yeh, I hear you want it pristine. Maybe someone else will prize it for that but also actually be able to fix it, stuffing parts if necessary to keep the original look.

[@splitprissm9339]

What in heck is an "Elephant Letter", as stated in the manifest shown at 5:30 ?

[@bandersentv]

Ha, nice catch. I have no idea?!?

[@antoniosantos6442]

😊

[@zundfolge1432]

I have the sencore CR-70. Have you ever serviced or replaced caps inside of it?

[@bandersentv]

Nope. Mine is from the 90s and I don't think it needs any new caps. Is there something wrong with yours?

[@zundfolge1432]

@@bandersentv it works just never took it apart. I guess since one never powers up antique electronics like old tvs or 1920s 1930s radios without recapping to avoid damage I wasnt sure if this holds true for the cr70 tester. Same as the tv test pattern generator I have that someone suggested they have tons of tantalum caps in that that like to short.

[@bandersentv]

For sure the Leader LCG400 had a ton of tantalums. I don't think the CR70 does. There's a tightly packed circuit board with a few electrolytics.

[@williamsquires3070]

Hi Bob. One thing here doesn’t make sense: how can the CRT tester “test” for an open grid, when the grid element of the CRT - by design - isn’t supposed to be connected to anything else? Inter-electrode capacitance measurement, maybe? It doesn’t seem like the circuitry of the B&K 440 is sophisticated enough for that.

[@bandersentv]

It tests the ability of the grid to cutoff the electron flow.

[@williamsquires3070]

@@bandersentv - Wouldn’t that require HV, and a connection to the anode cap? Otherwise the electrons coming from the hot cathode will just sort of spread out with nothing to draw them towards the face of the CRT and - thus - past the grid(s).

[@bandersentv]

@@williamsquires3070 No. G2 has several 100 volts on it

[@williamsquires3070]

@@bandersentv So how do you test for G2 open, then? My understanding is that the G2 grid (metal cylinder in the neck assembly) is further away from the cathode than the G1 grid, so putting several hundred volts (+ w/respect to cathode) on G1, G2 won’t have much effect, if any. You need something beyond the G2 grid that’s positively charged w/respect to the hot cathode, then bring G2 negative w/respect to the cathode and watch for a change in the plate (anode) current.

[@bandersentv]

No cathode current if G2 is open. Think of it as the plate. It is often called the first anode and the HV the second anode. It is there to attract and get the electrons moving towards screen. It is typically around 400 volts with respect to the cathode. You do not need to put any voltage on the 2nd anode to test a picture tube. The only tester that ever did is the ill conceived Raytronic Beamer.

[@rlgrlg-oh6cc]

Could you measure capacitance of that grid with respect to some other electrode to see if it's connected? Does the data sheet for that CRT list a bunch of capacitances that you could test for?

[@SeekingTheLoveThatGodMeans7648]

If the grid was simply gone, I'd expect no picture, just a blank (or almost blank, if modulation is applied to cathode) raster. I'd wonder about the possibility of a high resistance leak from G1 to G2, positively biasing the tube. I'd do some investigative voltage measurements with this tube and a known normal good tube.

[@bandersentv]

G1 and G2 (AKA first anode) are physically quite far apart. You'll see that the 5AXP4 does actually produce an image but the grid modulation is very compromised. What I'm thinking is that it is damaged or the lead is making poor contact somewhere.

[@owenjacob5542]

i have a b&k 440 to and i hav the schematic i can scan it and emal it to you

[@bandersentv]

Thanks for the offer but I got a copy from radiomuseum.org