gassy 21fbp22 ?

[timmy]

hey guys is there any fool proof way to tell if a crt like a 21fbp22 is gassy. i have my 63 silvertone roundie and at the anode button there is blue marks stretching away from the button towards the dag and the blue marks are clearly in the glass, is this any indication of a problem with this 21fb. this set still has hv issues that im still trying to narrow down when maybe the crt is infact gassy to be giving me false indications of a flyback or anything else in the hv section when it may be the crt all all along.

[timmy]

this pic is the blue burn that is in the glass itself and it extends all the way down to the dag so i wonder if this is where the hv is going, to dag, ground. it also extends up to the other end of the dag but its not close as the bottom one is and it looks as if it is infact grounding and with hv present i dont know how it could not being pretty much right at the dag. or better yet how does this happen and what does it effect, looks to me that it would effect hv, starve the crt for the proper hv.

[zeno]

Ive never seen glass turn blue. If you think its loading down the
HV pull the anode & hook a HV probe on it. If its beam
current loading it pull the CRT socket & see if the HV comes up.
What ever the blue is it dont belong there.......

73 Zeno

[Username1]

Unless you can get others to agree, I think it's unlikely any arcing made the glass blue.
Unless it's some contamination. Does it scrape off....? If it's "in" the glass, then it was
there from day 1, I can't see arcing doing anything to glass....

You should be able to measure cathode current on the tube, it's the low voltage end of
the tube, and you should be able to measure each gun, I think current is listed on
the schematics.....? If there is HV issues, just turn the brightness up and down, and
check the HV, does it fluctuate more than 3-5KV ?? Is it near where it should be 20KV ?

[timmy]

did that already without the anode connected the hv will be low because the crt acts like a capacitor, and with the wire off it was low.

[timmy]

the blue is in the glass for sure but close to the surface. cannot be scraped. you can actually see where it originated from right at the hv button and worked out from there. the pic dont show but the blue on the bottom of the button goes right to where the dag starts, almost like hv seeks a ground and here it found it.

[Username1]

Yah, without connecting the tube, the HV lead most likely will not be accurate.
You need to do a current check, then you need to check Horiz output tube cathode current.
And be sure the other elements are ok, Regulator tube, rectifier, B+, b Boost, Focus, Horiz
yoke circuit.....

[timmy]

Originally Posted by Username1

Unless you can get others to agree, I think it's unlikely any arcing made the glass blue.
Unless it's some contamination. Does it scrape off....? If it's "in" the glass, then it was
there from day 1, I can't see arcing doing anything to glass....

You should be able to measure cathode current on the tube, it's the low voltage end of
the tube, and you should be able to measure each gun, I think current is listed on
the schematics.....? If there is HV issues, just turn the brightness up and down, and
check the HV, does it fluctuate more than 3-5KV ?? Is it near where it should be 20KV ?

the hv has never been where it should be bright up certain scenes will lower to 19kv.reg circuit seems to be working but hv is not high enough to go into regulation to begin with.

[timmy]

Originally Posted by Username1

Yah, without connecting the tube, the HV lead most likely will not be accurate.
You need to do a current check, then you need to check Horiz output tube cathode current.
And be sure the other elements are ok, Regulator tube, rectifier, B+, b Boost, Focus, Horiz
yoke circuit.....

did all of this, cathode currant is at 190 and it can swing up or down. reg tube and others, whats odd is on the side of this blue i am having problems with centering on that side. focus volts seem to be ok at about 4500kv sams shows.

[Username1]

You may need to check wave shapes around the horiz osc. Did you replace all the caps?

[Username1]

Is that 190 current agree with the schematic?

[timmy]

yup lots of caps and those caps and resistors in and around the horiz.

[timmy]

sams says 200ma but i set it for 190 but at 200ma makes no difference with hv.

[Username1]

What is that centering problem ?

[timmy]

the screen is to much to one side and dont have enough room on the pot to center it as its maxed. screen is full but not right. to much weird stuff going on since i got this set.