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  #46  
Old 01-13-2015, 01:26 PM
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miniman82 miniman82 is offline
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If you mean .93ma with a dark screen and HV set to max, that's your problem. Most of the Sams I've read for roundies specify .8ma with a dark screen, HV set to whatever the schematic calls for. If you're pulling any more than that, chances are you're getting close to melting the 6BK4 as you're likely exceeding it's dissipation. You see HV schematic information has more to to with the regulator tube than it does the chassis.

For example, the 6BK4B (which is what most will have in their chassis) is rated at 40 maximum plate watts. Taking into account a 20% tolerance, this tube can be expected to dissipate somewhere around 32 watts continuously. Typically it comes to around 25 watts though, RCA designed the shunt circuit conservatively to maximize the shunt tube's life.

So for your example with a dark screen and the HV pot at 'low' and drawing 1.64ma (assuming a 23kv anode), that comes to 37.7 watts- easily above what RCA would have designed it to do, and dangerously close to the tube's maximum dissipation. I strongly suspect that if you look at the tube's structure under those conditions with a darkened room, you'll see the plate glowing which can be seen reflected off the bottom part of its structure (the part containing the grid and cathode, it's usually shiny so you can see stuff in it).

For the other example: .93ma@23kv=21 watts which is much better but again, outside what I would consider normal for a shunt tube which should be closer to .8ma. Obviously whenever you have something on screen, shunt current should drop as the CRT beam current picks up where the regulator left off. You should check to make sure the shunt tube's cathode current drops as brightness increases, if not the regulator circuit is suspect. Also take a look at your B+boost voltages, as that's where your regulator is taking its reference voltage from. If B+boost is jacked, so will regulator cathode current as the grid receives it's marching orders from whatever B+boost is doing.
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  #47  
Old 01-13-2015, 01:49 PM
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Yah, miniman hit it with what I was looking for, the bias in the tube is pretty high....
Quote:
For the other example: .93ma@23kv=21 watts which is much better but
again, outside what I would consider normal for a shunt tube which should be
closer to .8ma. Obviously whenever you have something on screen, shunt
current should drop as the CRT beam current picks up where the regulator left
off. You should check to make sure the shunt tube's cathode current drops as
brightness increases, if not the regulator circuit is suspect. Also take a look at
your B+boost voltages, as that's where your regulator is taking its reference
voltage from. If B+boost is jacked, so will regulator cathode current as the
grid receives it's marching orders from whatever B+boost is doing.
I was going to ask about those current readings, are they ma. and how accurate
do you think your meter is...?
Also that voltage I asked about B+ Boost, you did not post a number...?
You need to measure these things today, not look up your old posts, we need
to clarify exactly what is happening.... Your B+ Boost could be too high, this could
be why the voltages at the reg. are higher than the schematic says they should be...

.
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Last edited by Username1; 01-13-2015 at 01:59 PM.
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  #48  
Old 01-13-2015, 03:13 PM
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Quote:
Originally Posted by miniman82 View Post
If you mean .93ma with a dark screen and HV set to max, that's your problem. Most of the Sams I've read for roundies specify .8ma with a dark screen, HV set to whatever the schematic calls for. If you're pulling any more than that, chances are you're getting close to melting the 6BK4 as you're likely exceeding it's dissipation. You see HV schematic information has more to to with the regulator tube than it does the chassis.

For example, the 6BK4B (which is what most will have in their chassis) is rated at 40 maximum plate watts. Taking into account a 20% tolerance, this tube can be expected to dissipate somewhere around 32 watts continuously. Typically it comes to around 25 watts though, RCA designed the shunt circuit conservatively to maximize the shunt tube's life.

So for your example with a dark screen and the HV pot at 'low' and drawing 1.64ma (assuming a 23kv anode), that comes to 37.7 watts- easily above what RCA would have designed it to do, and dangerously close to the tube's maximum dissipation. I strongly suspect that if you look at the tube's structure under those conditions with a darkened room, you'll see the plate glowing which can be seen reflected off the bottom part of its structure (the part containing the grid and cathode, it's usually shiny so you can see stuff in it).

For the other example: .93ma@23kv=21 watts which is much better but again, outside what I would consider normal for a shunt tube which should be closer to .8ma. Obviously whenever you have something on screen, shunt current should drop as the CRT beam current picks up where the regulator left off. You should check to make sure the shunt tube's cathode current drops as brightness increases, if not the regulator circuit is suspect. Also take a look at your B+boost voltages, as that's where your regulator is taking its reference voltage from. If B+boost is jacked, so will regulator cathode current as the grid receives it's marching orders from whatever B+boost is doing.
dark screen brightness down hv pot set to min, ma is 1.64 hv pot max , 0.93 brightness up hv pot set to min 1.16 hv pot set to max 0.20 and the dvom i use i do trust it i did compare with another meter to be certain. the 6bk4 dont even get all that hot to the point of melting, no where near. i cannot get 23kv even to stay for a moment. i will have to check the exact b+ voltage under a load, where would the best place be to take this reading at this point ? and yes this is milli amps. the sams show the voltages and they are not far off it seems to me unless 5-10 volts would make a world of difference, i dont know.
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  #49  
Old 01-13-2015, 03:29 PM
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The current seems high as miniman explained. And since the reg is working off b+boost
we will have to figure it out... We're trying with the clues we have.... I got one
of the rca schematics off the internet, it says 390v and 376v to grid of 6bk4, you
have 402, and 390V grid I believe.... So lets look at your B+ voltages.....
Check them right off the caps in the PS.... 405V-c125 160mfd.,
386V - c120A 80mfd, and I think the last was 276V c-120b 50mfd.

Does your schematic have a total current for the HV output...?
as in picture tube plus HV reg....? and an acceptable way to
determine total....? As per sams.... to be accurate...



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Last edited by Username1; 01-13-2015 at 03:32 PM.
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  #50  
Old 01-13-2015, 03:37 PM
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Sure would be easier to follow this thread if there were some daggone punctuation...


From what I gather, the regulator seems to be working as it should. You said you put a new fly in it? You probably wired it wrong, there's no reason for HV to be drooping like this.
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  #51  
Old 01-13-2015, 03:45 PM
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Quote:
Originally Posted by Username1 View Post
The current seems high as miniman explained. And since the reg is working off b+boost
we will have to figure it out... We're trying with the clues we have.... I got one
of the rca schematics off the internet, it says 390v and 376v to grid of 6bk4, you
have 402, and 390V grid I believe.... So lets look at your B+ voltages.....
Check them right off the caps in the PS.... 405V-c125 160mfd.,
386V - c120A 80mfd, and I think the last was 276V c-120b 50mfd.

Does your schematic have a total current for the HV output...?
as in picture tube plus HV reg....? and an acceptable way to
determine total....? As per sams.... to be accurate...


ok this chassis is a clone and i have the sams for it and i show 370 and 385 and yes the voltages i posted have not changed and they are kind off high, i think around 15 volts. and the highest on the b+ is 400 volts and 390 volts and i knmow it was right but i will check it again to be certain this time and i will write everything down. the sams shows that the hv regulator current should not be less then 850 microamperes . it says to adjust to 23kv but i cannot get it there. he suggested in the first paragraph that the hv pot was maxed but it was not it was counter clock so thats why i put the specs up again. other then the voltages the other is ma.
.
omg this set
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  #52  
Old 01-13-2015, 03:50 PM
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Quote:
Originally Posted by miniman82 View Post
Sure would be easier to follow this thread if there were some daggone punctuation...


From what I gather, the regulator seems to be working as it should. You said you put a new fly in it? You probably wired it wrong, there's no reason for HV to be drooping like this.
yes it is a new flyback and this set always had a hv issue but i thought i had found the problem when i changed the fly i discovered the 1v2 was wired wrong and since correcting that the focus voltage and the overall focus had much improved. i found the mistake and corrected it and checked other areas for other mistakes and having the sams i was able to check areas and fix the wiring mistake. i also double checked all the work i had done by the sams and found none.
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  #53  
Old 01-13-2015, 03:58 PM
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Quote:
Originally Posted by miniman82 View Post
Sure would be easier to follow this thread if there were some daggone punctuation...


From what I gather, the regulator seems to be working as it should. You said you put a new fly in it? You probably wired it wrong, there's no reason for HV to be drooping like this.
Yes, he said new fly, and he rewired the focus circuit because something was wrong...
I thought something may be wired wrong too, that is why I asked the questions
about Horiz. Centering, and focus the other day... I figure if they work, and have
some reasonable range, then maybe there is no mistake...... In one of the
earlier threads I also asked about the new fly, and if all the contact points
were correct, or if there were mods on any install note sheet....

It would be cool if someone with recent experience on this chassis takes the point....

That reg. circuit is too simple to be causing all this trouble....

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  #54  
Old 01-13-2015, 04:05 PM
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Quote:
Originally Posted by Username1 View Post
Yes, he said new fly, and he rewired the focus circuit because something was wrong...
I thought something may be wired wrong too, that is why I asked the questions
about Horiz. Centering, and focus the other day... I figure if they work, and have
some reasonable range, then maybe there is no mistake...... In one of the
earlier threads I also asked about the new fly, and if all the contact points
were correct, or if there were mods on any install note sheet....

It would be cool if someone with recent experience on this chassis takes the point....

That reg. circuit is too simple to be causing all this trouble....

.
well there were no mods or special notes in this set. the hv reg does look simple but i have this set for 2 years plus and was never able to find whats going on with it . so i might just as well try the crt from my other set because of the mark on the inside of the glass on the crt thats in the set now was not there when i first got it but over a small amount of time this set has on it since i have the mark appeared so maybe the interior dag somehow is damaged and causing all of this i dont know but ill have to rule it out once and for all.
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  #55  
Old 01-13-2015, 04:28 PM
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Can you post a picture.....? I'm gunna say I don't think you have any inside tube
coating problem.... You would have arcing, or some other problems.... Just not sure....

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  #56  
Old 01-13-2015, 04:31 PM
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Quote:
Originally Posted by Username1 View Post
Can you post a picture.....? I'm gunna say I don't think you have any inside tube
coating problem.... You would have arcing, or some other problems.... Just not sure....

.
my computer that has the pic of the mark on the inside of the crt i cant use it at this moment but it is here on karma under 21fbp22 crt there is a good pic of it. let me know if you cant find it.
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  #57  
Old 01-13-2015, 04:33 PM
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the pic of the crt is on page 6 under gassy 21fbp22
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  #58  
Old 01-13-2015, 05:02 PM
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I remember it now..... I'm not concerned about it.... Don't think it's a problem...

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  #59  
Old 01-13-2015, 05:07 PM
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well i dont know at this point, but i do really appreciate the help from all the members here and i do try but at the same time i was never a tv tech and i really im sorry for driving everyone here crazy with this nutty silvertone.
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  #60  
Old 01-13-2015, 06:50 PM
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Well, since you got this set with HV problems, and found some wiring mistakes in the
focus area, you should take a few steps to ensure that no problems were introduced
be work done by someone else..... I think you should get, or borrow a good camera,
take pictures of the flyback, the wiring, and under the chassis, post good clear picts, and
some the focus wiring you found and repaired.... There are people here who have
recently worked on and own several of them.....

You might also find that if both of your sets are identical, as far as the chassis goes,
that visual comparison might be a very good idea.... I'm confident the problem can
be found, there are lots of people here who know this chassis inside out....

By the way, which Silvertone is this one.... 63, or 65...? And are they the same.....


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