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  #61  
Old 11-22-2013, 01:14 PM
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Bill Cahill Bill Cahill is offline
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I know what ohm's law is. But, I don't care. That just isn't enough wattge. Period.
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  #62  
Old 11-22-2013, 02:04 PM
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Originally Posted by Kamakiri View Post
Just to clarify, I did a soft start on a variac, but not too slowly....I took about 20 seconds to bring it up to voltage. Initially, the reading was 305 volts, and dropped to 235 on the first try, with the one resistor in place. The voltage reading was tested at the B+ point that was on the schematic on the previous page in this thread.

I then shut it down, put in a second resistor in place, then again with a quick variac power up, the reading briefly stabilized at around 253 volts. I noticed that I had a full raster, snow, and static in the audio....exactly the way it should be. Observed it only for a few seconds, then went back to the meter and noticed that it started jumping all over the board, ranging from 240-260 volts. When I caught a light odor of something, I shut the set down immediately.
I'm still trying to understand this sequence... it appears that with one 39 ohm resistor in series with the diodes to the B+ test point, there was no problem other than the B+ voltage being slightly too low? The resistor did not overheat ... correct?
Then you put a second 39 ohm resistor in parallel with the first to increase the B+, which it did, but then the voltage started jumping around and one resistor started smoking? Was the first resistor still ok? Putting the two identical resistors in parallel would have reduced the voltage drop across the resistor(s) and, therefore reduced the power dissipated by the resistors(s) as well as splitting that power between the two. Neither should have overheated. Perhaps the second resistor was defective?
If it were mine, I would try again with a fresh resistor and monitor the current in series with the resistor pair.
jr
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  #63  
Old 11-22-2013, 02:51 PM
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The first resistor is what smoked, the second was fine. Strange, but true...unless the first resistor started to crispify at the first test, and I didn't notice.

At this point, Findm-Keepm's advice had got me this far, as far as the values of the resistors, and precise directions on how to hook things up and arrive at the proper specs. Bill Cahill's advice of a 25 watt resistor to do this job right will only cost me about $5, for a good Dale chassis mount resistor with a heat sink.

That said, everyone here seems to agree that a 25 watt resistor here will certainly not hurt anything, at worst it's crazy overkill....at best, it's the proper part....so that's the way I'm going to go. I'll check back into this thread in a few days when the Mouser order arrives.

I certainly do appreciate the input and education I've been given thus far
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  #64  
Old 12-01-2013, 07:04 AM
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Finally got the resistor in from Mouser. The only bad thing is that I must not have left that prior resistor in circuit long enough.....the chassis voltage with this one in line dropped to 243V. Should be at 255

I do have to say, the 18 ohm RH series Dale resistor I put in is getting HOT. Handling the set fine, but it sure is warm.

Picture isn't fantastic, reception wise, but the tuner in this set isn't the greatest and I'm using clip leads for an antenna picking up signal from my agile modulator. I'm going to button it up for the moment and move it to cable and see where we're at. The chassis voltage is off by -12V, meaning that I'll have to probably order yet another resistor, but I want to let it play out a little where it is and see how it looks. The picture filled out nicely as opposed to where it was before.
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  #65  
Old 12-01-2013, 08:04 AM
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Here's where I'm at right now. Seems to have some slight blooming, which I assume is due to the low voltage on the chassis.

http://www.youtube.com/watch?v=_bUxH...ature=youtu.be
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  #66  
Old 12-01-2013, 12:53 PM
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IMHO you should prepare for smoke! Something is wrong, the set should not be drawing enough current to get an 18 ohm 25 watt resistor *really* hot!

Calculator:
http://www.crownaudio.com/ohms-law.htm

If you plug in 18 ohms and, say 15 watts (my estimate of what it might take to get a 25 watt resistor fairly hot), you will find a voltage drop of about 16.4 volts (too much drop) and a current of about 900 ma! Since the original rectifiers were only 340 ma or so, it would appear that the set is drawing more current than it should,
just my 2 cents,
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  #67  
Old 12-01-2013, 12:58 PM
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If that's the case, what the heck would cause that in a TV that by and large is running as it should?
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  #68  
Old 12-01-2013, 01:19 PM
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I don't know, perhaps an infant failure of one of the new electrolytics. Can you measure the current in series with the resistor?

Am I correct in assuming that the resistor is indeed, bolted to the chassis? If not, it could reach a high temperature at less than its rating.

jr
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  #69  
Old 12-01-2013, 02:10 PM
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No, at the time, I had the resistor put in with clip leads. I didn't want to hard mount it to find out I needed a different value.
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  #70  
Old 12-01-2013, 02:27 PM
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Originally Posted by Kamakiri View Post
No, at the time, I had the resistor put in with clip leads. I didn't want to hard mount it to find out I needed a different value.
OK, I don't know what the "free air" dissipation of the resistor might be, possibly it could get pretty hot if dissipating, say only 5 watts... where does that take us? Plugging in 5 watts and 18 ohms into the equation yields about 9.5 volts drop (but you say you are 12 volts too low) and about 500 ma current (but the orig rectifiers were only 350 ma or so). IMHO, something downstream is drawing more current than the original design called for.

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  #71  
Old 12-01-2013, 05:18 PM
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Add to that the blooming. There was no blooming of the picture when the seleniums were in place. Also now, if you look really hard at the video, you can see a very light line going down the center of the screen, which isn't really visible on some stations. Is that horizontal foldover?

So then we're left with the question, is the blooming caused by the low B+, or is the same component causing the blooming and low B+, dragging the chassis voltage down, and sucking current?

First thing I'm going to do is test the diodes. Not sure if another diode in series would help matters much, as I got 3 watt diodes. Next thing, I'll re-test the tubes. Beyond that, I just don't know.....
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  #72  
Old 12-01-2013, 05:25 PM
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If you connected a doubler cap backwards that could do it.
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  #73  
Old 12-01-2013, 05:33 PM
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I would first try to measure the current in series with the resistor, to see what the set is drawing off of the B+ line... that should answer the question; "is the set drawing too much current or is the power supply not working correctly?".

jr
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  #74  
Old 12-01-2013, 11:36 PM
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Bill Cahill Bill Cahill is offline
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I agree checking the current is one of the best ways to find out what's happening. But, the blooming, along with slightly short width, which he told me about, and, the white line in middle, which sounds like slight horizontal fold over, obviously, hv is low. I'm not sure if that is caused by low voltage, or, something wrong in hv section. In fact, if the screen resistor on the horizontal output, or, even the cathode resistor on same, if it uses one, which often they do, that would cause that section to draw more current, causing the power supply to drag down.
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  #75  
Old 12-02-2013, 10:43 AM
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Went to measure the current draw, but then realized that the ammeter function on my meter isn't working. Have to go pick one up today or tomorrow.
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