#31
|
||||
|
||||
Quote:
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. |
#32
|
||||
|
||||
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. Last edited by bandersen; 09-04-2014 at 01:36 PM. |
#33
|
||||
|
||||
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 |
#34
|
|||
|
|||
Bob, I found a similar set on craigslist. Too bad it is in Texas.
http://dallas.craigslist.org/mdf/atq/4628868624.html |
#35
|
||||
|
||||
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. Last edited by bandersen; 09-08-2014 at 03:28 PM. |
Audiokarma |
#36
|
||||
|
||||
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. |
#37
|
||||
|
||||
Yep, fuse blew. Now to determine why...
|
#38
|
||||
|
||||
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. |
#39
|
||||
|
||||
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. |
#40
|
||||
|
||||
Quote:
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. |
Audiokarma |
#41
|
||||
|
||||
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.
__________________
Dumont-First with the finest in television. |
#42
|
|||
|
|||
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 |
#43
|
||||
|
||||
Quote:
The drive control is a pot. I'll try replacing the cap and measure all the voltages and waveforms in the horizontal circuits.. Quote:
Quote:
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. |
#44
|
||||
|
||||
Quote:
Quote:
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. |
#45
|
||||
|
||||
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. |
Audiokarma |
|
|