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Old 07-13-2017, 03:03 PM
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Philco 7053 CRT Checkers

I have two Philco 7053 CRT checkers, in which I’ve replaced the usual passive components, cleaned the pots and switches, and provided good NE45 indicator bulbs. They should work.

I’ve used both instruments to check a 7JP4 and a 12LP4. The cathode-heater and cathode-grid short tests show “no short” as expected for both CRTS.

However, the “beam current test” (I have no clue how this works) gives a zero result--no neon glow at all--for both instruments on both CRTs. So, there are four possibilities:
(1) Both CRTs don’t work or
(2) Both test instruments don’t work or
(3) Both CRTs and both test instruments don't work or
(4)These old tubes, even with some life left in them, shouldn’t be expected to register any result.

What do you think?
Thanks,
Henry
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Old 07-13-2017, 03:37 PM
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Perhaps you should look for a working 50's TV so you have a known good tube to test your tester....Another option would be to take a known good 6BK4 and wire it up to the tester and see what it does.

6BK4 tubes have similar characteristics to the average electron gun so they might be a good sanity check in this case.
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Old 07-13-2017, 04:32 PM
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The 7JP4 was working when the set was fully assembled several years ago. The next time I order tubes I'll look for a 6BK4--the CRT checker does have an octal socket.
Thanks.
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Old 07-15-2017, 12:57 AM
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Perhaps try a micro ammeter in series with the anode or cathode connection from the tester to see if you can measure any current at all.

jr
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Old 07-17-2017, 12:24 AM
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Adapting the 7053 to a 6BK4

I now have some idea about what “beam current” is and how the CRT checker measures it. The Beltron 808A instructions say that .85 mA is the minimum for an acceptable CRT. I assume that the Philco 7053 “weakest” reading would be similar to the Beltron’s minimum performance level. When I tested the 12LP4 previously with the Beltron, the reading was in the neighborhood of .45 mA. At the 7053’s “weakest” setting, the 12LP4 may be producing only half of the beam current needed to get the neon lamp glowing.

Of the three suggestions for checking the 7053 beam current test function, two are impractical. I’m not going to look for a working TV, and my multimeter’s limitations preclude a reliable current reading at the needed level.

The third suggestion was to test a 6BK4 in place of a CRT. I can get a 6BK4 and adapt the 7053’s Octal socket to its base. I thought that would be straightforward, but I am confused about the 7053 instructions.




The heater, grid, and cathode connections are straightforward, but which 7053 pin is used for the anode, and does it connect to the 6BK4 cap?
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Old 07-17-2017, 01:02 AM
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I would connect pin 4 from the tester to the plate cap of the 6bk4.

What multimeter are you using that can't measure currents in the few hundred micro amp range?

jr

Last edited by jr_tech; 07-17-2017 at 01:09 AM. Reason: add question
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Old 07-17-2017, 02:02 AM
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Thanks. My trusty Radio Shack 22-811 and a Klein Tools meter both state a lower limit of 0.4 mA. I don't get consistent capacitance readings when I'm close to the lower limits, and I didn't expect more reliability from the ammeter. Other than that, it's a bit awkward to get the meter in series with one pin of a plug.
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Old 07-17-2017, 08:54 AM
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You're going through a lot of work to test the 7JP4. The 7JP4 CRTs are well known for testing good on a tester, but not having enough brightness in actual use. This is the reason why testing a 7JP4 in a working set is the oft recommended method.

More info here:

http://www.videokarma.org/showthread.php?t=265455

Quote:
Originally Posted by bandersen View Post
I've tested 20 or so 7JP4s and all had very good emissions on the CR70, but definitely vary in brightness when actually used.

.
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Old 07-17-2017, 10:27 PM
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This is Not "Work"

This is for fun. It's experimentation for the sake of learning and the joy of discovery. I already know the condition of the CRT. The set has been out of service for several years, but this is what it was like before I "fixed" it.

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Old 07-17-2017, 11:58 PM
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There are not too many 7 inch electrostatic sets with a "double d" display format... is it an Emerson?

jr
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Old 07-18-2017, 12:18 AM
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Admiral 17T12.
I set up the 6BK4 on the 7053 CRT checker. Got the expected result on the shorts tests, but nothing on the beam current test. I put the multimeter in series with the anode and got about 45 volts. In the heater-cathode and grid-cathode positions I got 0.8 mA, but no current in the beam current test.

I'd like to try your suggestion for checking current with a CRT, but am I doing this right? I simply put the meter between the plug and socket in the anode pin position?
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Old 07-18-2017, 12:48 AM
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Ahhhh! I have never seen a 17t12 in the flesh!

Yep, that is how I would connect it.

jr
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Old 07-18-2017, 02:38 AM
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It's a 17T12 Chinese!
Here are some photos:
https://flic.kr/s/aHsm4JasR6

Here's a thread from five years ago:
http://www.videokarma.org/showthread.php?t=255581

I'll play with the CRT Checker tomorrow.
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Old 07-22-2017, 06:25 PM
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I had a dream last night. Actually I had several dreams, but one interesting dream had me fiddling with the Philco 7053 CRT checkers again. The instrument was connected to the 12LP4, set on “beam current test,” and (as with all previous tests) the indicator lamp would not light. Then suddenly, for no apparent reason, the neon lamp flickered on. Then I woke up and felt disappointed that it was only a dream.

This morning I went back to the CRT checker connected to the 12LP4, trying to measure current from the cathode. I was reading 0.15 mA and the indicator stayed dark. I spent the next 30 minutes aimlessly checking voltage and current between every conceivable point at each test setting. Finally, I had the meter connected across the indicator lamp. Suddenly, for no apparent reason, the neon lamp flickered on--and the instrument happened to be set for beam current! I disconnected the multimeter, and shut everything down. Then I powered up again, let it warm up, and repeated the beam current test, and it worked again. Then I connected the other 7053, and it worked, too.

Go figure.

I guess I finally had the cathode hot long enough to wake up the CRT. Maybe I’ll remember this next time.
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