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  #31  
Old 09-02-2014, 09:16 AM
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NoPegs NoPegs is offline
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Quote:
Originally Posted by bandersen View Post
Here's a closer look at one of the oddball resistors in this set. It's a Rosenthal which I think is German.

Rosenthal, "Ja, Deutschland!"


They're now part of the glorious Vishay empire.

http://www.vishay.com/landingpage/50year/draloric.html

Last edited by NoPegs; 09-02-2014 at 09:27 AM.
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  #32  
Old 09-03-2014, 02:33 PM
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I found a couple fried dogbones in parallel. Enough paint remained for me to identify them as 47K which matches one version of the schematic. Together they should measure 23.5K but I got about 5K.


Underneath them was an even crispier resistor which I can't make out. Again, the schematics for this circuit vary widely, but I'm fairly certain it should be 33K - not 7K.

I wonder hat caused the failures ? I'll replace them and keep my fingers crossed.
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Last edited by bandersen; 09-04-2014 at 01:36 PM.
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  #33  
Old 09-05-2014, 09:10 AM
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That sure is an interesting(strange) set. It's neat watching it slowly come back to life. Outside of the Farnsworth in the ETF museum I have only ever seen one other Capeheart-Farnsworth product and that was at an antique store years ago and they wanted $500 for it!

As for all the differences, maybe undocumented production runs but also far be it for Sams to be flat out wrong!

Matt
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  #34  
Old 09-08-2014, 03:01 PM
azbigsam azbigsam is offline
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Bob, I found a similar set on craigslist. Too bad it is in Texas.
http://dallas.craigslist.org/mdf/atq/4628868624.html
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  #35  
Old 09-08-2014, 03:20 PM
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I stayed up late list night I finally tried to power it up The 8XP4 test CRT is at add odd angle because of the stiff spring around the HV lead.

As soon as I tuned in channel 6, I god strong clear sound No picture though and no HV.


I discovered the 1/4 amp flyback fuse was open and tacked a new one across it.
013

Yay! A blurry raster


After some more control twiddling, I got a blurry but stable image.


I figured the image was blurry because of the focus coil messing up the auto focus CRT. It's part of the power supply so can't be disconnected but I was able to unmount it.


Ah, much better


Next up, I'll test all the tubes and do some more tweaking.
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Last edited by bandersen; 09-08-2014 at 03:28 PM.
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  #36  
Old 09-08-2014, 09:38 PM
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Well I found and replaced some weak tubes and the set was playing better. Then while making some control adjustments I hear a faint pop and saw a brief spark near the HV rectifier and the picture went dim

I sure hope it's something simple like the HV rectifier died or fuse blew.
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  #37  
Old 09-08-2014, 09:43 PM
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Yep, fuse blew. Now to determine why...
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  #38  
Old 09-08-2014, 10:33 PM
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Yep, fuse blew. Now to determine why...
sounds like the 6W4 damper tube failed with a fil to cathode short. the best thing to do is just replace the 6W4 with a 6AX4. also chect to see if that disk capacitor underneath the damper tube shorted out. i have seen these short out before.

Last edited by robert1; 09-08-2014 at 10:36 PM.
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  #39  
Old 09-09-2014, 12:11 AM
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The 6W4 tested OK but I replaced with a NOS 6AX4 anyway. Replaced the fuse too. That got HV back until I tweak the drive control when I got a flash and the fuse blew again. Still not sure exactly where the flash came from. Might have been the fuse itself.

Before it died I managed to test the HV and it was only 6.5 kV - should be closer to 11 kV. Something sure isn't right in that circuit.
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  #40  
Old 09-09-2014, 08:15 PM
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The 6W4 tested OK but I replaced with a NOS 6AX4 anyway. Replaced the fuse too. That got HV back until I tweak the drive control when I got a flash and the fuse blew again. Still not sure exactly where the flash came from. Might have been the fuse itself.

Before it died I managed to test the HV and it was only 6.5 kV - should be closer to 11 kV. Something sure isn't right in that circuit.
since i don't have a diagram to look at for that chassis, i could only ask a couple of things. is the horizontal drive control a adjustable coil?, or a variable capacitor? or a pot? if it is a coil type, usually, those have a capacitor across it. it might be leaky. the coil itself, may have shorted windings.

have you checked the current on the cathode of the 6BG6?

i still suspect that red disk capacitor underneath the damper tube socket.
it appears to me that something is drawing too much current in the output stage. it might be that the flyback xfmr may a a few shorted turns or any of the above mentioned things, it also could be caused by a problem in a different circuit protected by that fuse.
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  #41  
Old 09-09-2014, 09:54 PM
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Nice to see you making progress, even though there's been a couple of bumps along the way. When you get the bugs worked out, shoot me a PM and I'll get those knobs and the nameplate/control cover out to you.
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  #42  
Old 09-09-2014, 10:24 PM
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Hi Bob,

I have a question about the small test CRT tubes you use. After you get a set to work with a test tube, do you need to readjust the set again when the full sized tube is installed?

Also, I am thinking these tubes do not use an ion trap, true?

Is the focus coil a problem?

Steve
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  #43  
Old 09-10-2014, 10:56 AM
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Quote:
Originally Posted by robert1 View Post
since i don't have a diagram to look at for that chassis, i could only ask a couple of things. is the horizontal drive control a adjustable coil?, or a variable capacitor? or a pot? if it is a coil type, usually, those have a capacitor across it. it might be leaky. the coil itself, may have shorted windings.

have you checked the current on the cathode of the 6BG6?

i still suspect that red disk capacitor underneath the damper tube socket.
it appears to me that something is drawing too much current in the output stage. it might be that the flyback xfmr may a a few shorted turns or any of the above mentioned things, it also could be caused by a problem in a different circuit protected by that fuse.
You can download a copy of the Sams here: http://www.earlytelevision.org/pdf/C...Sams_160-2.pdf

The drive control is a pot. I'll try replacing the cap and measure all the voltages and waveforms in the horizontal circuits..


Quote:
Originally Posted by truetone36 View Post
Nice to see you making progress, even though there's been a couple of bumps along the way. When you get the bugs worked out, shoot me a PM and I'll get those knobs and the nameplate/control cover out to you.
Thanks, I sure will!

Quote:
Originally Posted by HighHopes View Post
Hi Bob,

I have a question about the small test CRT tubes you use. After you get a set to work with a test tube, do you need to readjust the set again when the full sized tube is installed?

Also, I am thinking these tubes do not use an ion trap, true?

Is the focus coil a problem?

Steve
Yes, you need to readjust, the height, width, linearity etc. They do not use an ion trap and are self focusing.

Leaving the focus coil in place does produce a blurry image. That's why when I unmounted it in the photos above the picture improved.
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  #44  
Old 09-10-2014, 01:20 PM
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You can download a copy of the Sams here: http://www.earlytelevision.org/pdf/C...Sams_160-2.pdf
Thanks!, Bob

Quote:
Originally Posted by bandersen View Post
The drive control is a pot. I'll try replacing the cap and measure all the voltages and waveforms in the horizontal circuits..
Acording to the diagram, that .25 amp fuse protects the screen grid on the 6BG6. it also supplies voltage to the horizontal drive control as well as the damper circuit. the first thing i would do is place a milliameter between the cathode of the 6BG6 & the -100 volt source that is currently connected to the cathode of the H.O.tube. power the set up & monitor the meter reading. if it is rising & starting to go over 250Ma, it is possible that the 6BG6, itself, has developed grid leakage that does not appear when it is cold. you can also sub another 6BG6 to see if it does the same thing.

about anything could be causing the fuse to blow, however the most obvious things would be the H.O.tube, the horizontal drive pot that has "whiskers" in it, the Screen resistor (r88 22k) that has lowererd it's resistance.
i would check these things first.
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  #45  
Old 09-11-2014, 12:54 AM
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A bit off topic but perhaps one of these is your set.
In any case there's a fair chance it passed through that guys hands at some point.

Capehart assembly line circa 1951.

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