#46
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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
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Yah, miniman hit it with what I was looking for, the bias in the tube is pretty high....
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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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Yes you can call me "Squirrel boy" Last edited by Username1; 01-13-2015 at 01:59 PM. |
#48
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#49
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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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Yes you can call me "Squirrel boy" Last edited by Username1; 01-13-2015 at 03:32 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
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#53
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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
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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
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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
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the pic of the crt is on page 6 under gassy 21fbp22
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#58
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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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Yes you can call me "Squirrel boy" |
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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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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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