21fb j p22

[timmy]

Well at least I know I have a good tube in this Motorola because the RGB adjustments are all even alittle less then half up and have a nice white screen.

[Yamamaya42]

Another thing that tells the health of your tube is how far up you must set the crt bias adjustment to get a balance on the grayscale setup, the lower the better, or "master G1" as they call in on your set.

[timmy]

Originally Posted by Yamamaya42

Another thing that tells the health of your tube is how far up you must set the crt bias adjustment to get a balance on the grayscale setup, the lower the better, or "master G1" as they call in on your set.

The G1 is set like a 1/4 up very low.

[timmy]

I have a spare 21fb and testing it on 2 different bk440 testers shows the red gun is weak but when I check the tube in the moto it shows all 3 guns are good on the 440 testers but I have a bk tester from 1978 and both tubes show good all 3 guns I don’t get why the newer bk shows the tube with the weak red gun as good. I know 2 different testers but all work fine it’s odd. Which one do I believe.

[Yamamaya42]

Before you believe what the tester is telling you, hook a DVM to the heaters as you are doing the testing, to be sure that the heater voltage is not dropping below 6.3 VAC, that's the problem my tester has, b&k model 490b, it does NOT have the power to light up a color roundie, and drops below 5 VAC, I have to rig up a separate 3 amp 6.3 VAC source to test them correctly.

[timmy]

Originally Posted by Yamamaya42

Before you believe what the tester is telling you, hook a DVM to the heaters as you are doing the testing, to be sure that the heater voltage is not dropping below 6.3 VAC, that's the problem my tester has, b&k model 490b, it does NOT have the power to light up a color roundie, and drops below 5 VAC, I have to rig up a separate 3 amp 6.3 VAC source to test them correctly.

These 440 testers I have had for awhile now and all my other tubes in my sets tested good the heaters lit good only this one tube so I don’t think it would be the power that supply’s the heaters. The 440 testers on color is 7 vac

[Yamamaya42]

Well, it won't hurt to have that added insurance of sticking the DVM in ac mode on there to be sure when you test, I was in panic mode for a week before I worked it on on mine that it was over a volt too low. And if it's OK, you can look for other reasons.

[timmy]

Originally Posted by Yamamaya42

Well, it won't hurt to have that added insurance of sticking the DVM in ac mode on there to be sure when you test, I was in panic mode for a week before I worked it on on mine that it was over a volt too low. And if it's OK, you can look for other reasons.

Well there’s not much to look for so maybe that red gun heater is drawing more then the other 2 and not heating to the right level but then again the newer tester may put more current out to overcome that.

[Yamamaya42]

Or, (speculation), red is the weakest, and if... I mean IF the heater voltage is a tad low on the tester vs running at full power on a TV, or any other known good state, it could be the equivalent to a “life test” where the heater voltage is deliberately lowered to see which tired gun drops of first, not saying that this IS what is happening, but a simple DVM test will make sure, cause you never know what the voltage is at the tube test socket for sure.

[timmy]

Originally Posted by Yamamaya42

Or, (speculation), red is the weakest, and if... I mean IF the heater voltage is a tad low on the tester vs running at full power on a TV, or any other known good state, it could be the equivalent to a “life test” where the heater voltage is deliberately lowered to see which tired gun drops of first, not saying that this IS what is happening, but a simple DVM test will make sure, cause you never know what the voltage is at the tube test socket for sure.

I’ll have to check the voltage but if all 3 are good then it’s a mystery

[timmy]

I there any focus gain in using 3 22 meg resistors in series to make 66 meg or would it be the same as using a single 66 meg stick resistor.

[Yamamaya42]

Not really, other than improved HV creepage and clearance handling perhaps, the specialty 66m 6kv resistor will do fine as it was made for just that application, the only reason that early color sets had 3 22m resistors was that they had not created the specialty 66m one at the time and was not in mass production as it was later.

[timmy]

Originally Posted by Yamamaya42

Not really, other than improved HV creepage and clearance handling perhaps, the specialty 66m 6kv resistor will do fine as it was made for just that application, the only reason that early color sets had 3 22m resistors was that they had not created the specialty 66m one at the time and was not in mass production as it was later.

the 1963 silvertone I had with the ctc12 clone had the stick resistor unless Motorola decided to keep using 3 resistors maybe they didn’t trust the new stick resistor.

[Yamamaya42]

did you ever do the heater voltage tests?

[Yamamaya42]

Originally Posted by timmy

the 1963 silvertone I had with the ctc12 clone had the stick resistor unless Motorola decided to keep using 3 resistors maybe they didn’t trust the new stick resistor.

Or they just had a HUGE stock of 22m 6k resistors on hand!