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  #46  
Old 10-26-2018, 03:34 PM
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Originally Posted by Electronic M View Post
I'd like to know the tricks to finding those new door knobs. I've got a TM-21 with a dead shorted doorknob, and I suspect the somewhat unstable regulated HV level and slightly higher (than I like) H out current/temp in my 21CT55 may have something to do with bad doorknob caps.
I typed MuRata 1000pf 20kv, 2000pf 40kv into Mousers search and they came right up. Unfortunately many of them are now listed as End of Life: Scheduled for obsolescence and will be discontinued by the manufacturer.

https://www.mouser.com/ProductDetail...TXEZqe9w%3d%3d
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  #47  
Old 10-26-2018, 10:40 PM
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Originally Posted by Electronic M View Post
I'd like to know the tricks to finding those new door knobs. I've got a TM-21 with a dead shorted doorknob, and I suspect the somewhat unstable regulated HV level and slightly higher (than I like) H out current/temp in my 21CT55 may have something to do with bad doorknob caps.
Let me know what you're looking for and I'll see what I can find.

I replaced the reactance coil tonight. I had 3 or 4 NOS Miller or Meissner replacements but I couldn't figure out how they were supposed to work as the original had 5 terminals and these have 6. They all have one terminal painted with a green dot but the Philco had it on the opposite side. Well, I solved my problem because further digging in my box-o-coils turned up a genuine Philco "pull". It has a different suffix but my cross reference charts take it to the same replacement. I got that installed after supper and, since I could now get audio on the bench with a converter box connected, naturally I had to try it again with everything hooked up. This is when it gets to be fun! Plenty of work to do but I'm very happy with how this is turning out.
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  #48  
Old 10-26-2018, 10:58 PM
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Looking very promising.
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  #49  
Old 10-29-2018, 01:13 PM
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Already past HV repairs, video and locking in on color info, you got lucky with that part. You can see the right color differences in that screenshot on Les' Nessman's forearm, all despite the purity issue.
Keep the great progress rolling!
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Last edited by DavGoodlin; 10-29-2018 at 01:16 PM.
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  #50  
Old 10-30-2018, 02:46 PM
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Let me know what you're looking for and I'll see what I can find.
I'm looking for the following. 2500pF @ 30KV, 1200pF @ 15KV, and 1000pF @ 10KV. I'm probably going to get a 2000pF 40KV for the first one since I feel 30KV is under rated for a 25KV line that can do over 30 if the regulation fails, and Bob G has had success with that value...I think I can find the 1000 on mouser, but I'm not sure what to do about the 1200...it seems Murata does not make that value of door knob anymore according to the datasheet for that part family. If I can I'd like to go up 5-10KV on all the door knobs I order to ensure they last as long as I live (especially since they are getting discontinued). Also according to the datasheet the threaded ends only project about 1mm so I'm going to have to come up with something with the parts available at the local hardware store to match the 1" terminal projection of the originals.

If you rather we discuss this privately send me an email. My PM box is full.
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  #51  
Old 10-30-2018, 11:26 PM
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Tom, I'll try to email you soon.

I did have a setback. I finished replacing the last of the caps (all in the color circuit) and tied up some other little loose ends. The set powered up great. I was adjusting the HV to specs and it was very, very close. Then, without warning, HV went away. I was able to bring it back to some extent with an external horiz osc source but as of right now I have good voltages at the horiz. output, no red plating, no HV. Another clue: the Philco information (found at the ETF website-thanks Nick!) has you connect a meter in place of the sweep circuit fuse. It's supposed to read 2.1ma but I was getting 160ma. (Though now, on the bench, it's back to normal) I also noted excessive heat at the horizontal limiting coil. Even before this, I kept coming back to things not being right in the -25v line. So, I have it back on the bench and am slowly trying to troubleshoot. Oh, well, I went through a similar struggle with my CTC-5 many moons ago and it worked out in the end. I am anxious to get this behind me so I can start waking up the color circuit.
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  #52  
Old 12-05-2018, 10:31 PM
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I've been chasing this thing in circles for weeks now. Time to call in the calvary! Maybe some of you, who unlike me know what you're doing, can point me in the right direction? Part of the Photofact schematic is posted. To recap:

I had 26kv & a nice raster. As I was adjusting the HV I suddenly watched it fall while the HO tube cathode current jumped & the picture started to fade. I shut it down.

Where I'm at currently: HV is around 12kv with a dim raster, pulled in on the left about 1/4 of the screen. It takes perhaps 45 seconds for the HV to come up. Cathode current is on the high side. The horizontal limiter coil is getting very hot, and in short order; I put a meter on both sides of it and each is seeing over 200ma. After running a few minutes the core of the flyback is hot. There are no outward signs of distress to the flyback (no dripping wax, no cracks, no arcing). All resistance readings on the fly are correct.

The set has been recapped including the doorknobs. I didn't change C164-167 but did a quick & dirty sub with the closest thing I had on hand & nothing changed. I tried a temporary swap to a later RCA 21" yoke with no change. All tubes in the circuit have been swapped more than once with NOS. Disconnecting the HV regulator had no effect. I tried adding R268 & C239 which Philco added to later runs-no change. External sources for horiz drive made no change. Chassis voltages, last I checked, were good.

Anything I'm missing? I know the problem is right in front of me; I just can't see it.
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  #53  
Old 12-06-2018, 09:36 AM
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Could your damper have shorted? Also have you tried unhooking the doorknobs?.... I know they are new, but you can't rule out infant mortality.
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  #54  
Old 12-06-2018, 03:21 PM
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If I'm understanding you correctly, you recapped the doorknobs?

I've never seen one fail, but to each their own I guess.

One of your diode couplers likely isn't working, or the filament windings have shorted to ground. Did you restring them yet? I always do, wiring doesn't last forever...

If that's not it, I bet one of your new doorknobs went bad. Measure the voltage at each point in the doubler circuit, you'll probably find a loss somewhere.

I have a bunch of doorknobs ere if you need.
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  #55  
Old 12-06-2018, 10:16 PM
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1) The doorknobs. I had an early b/w set with a bad doorknob once; easy enough to repair. I have an assortment of "pulls". From what was on the webpage that Dave had for his TV123, he had to replace them due to a rectifier that was red-plating. I had a no-HV condition earlier in the resurrection process that was cured by changing them...I'm not sure which was bad. The 3 higher value caps were replaced with new production Murata units ($$$) while the one in the focus circuit is the same rating typically seen in early b/w stuff so I swapped in another I had on hand. Tonight I disconnected or swapped around the replacements with no change. While I was at it I also replaced the 4.7 ohm resistor in the base of the diode coupler.

2) I never thought about restringing the filament windings. I can't see anything obvious but its hard to tell what might be hidden where it wraps around. I have plenty of replacement HV wire so maybe I'll give it a try. This raises a question: is there any polarity that has to be observed? (I don't see how it could matter)

3) The damper-Nick included a NOS tube when I got it, plus I bought a spare. Swapping brought no change.

I need to reexamine the stack of 68mmf/5kv caps in the width coil/yoke circuit. I previously loosened one end and subbed something halfway close to see what would happen but nothing changed. Now that I have the HV cage all torn apart, my access is as good as it will ever be. I should just order some and be done, whether they're good or bad. I'm not sure how failure prone they are-I guess they're ceramic.
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  #56  
Old 12-07-2018, 01:36 PM
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No polarity, it's heaters.

The wiring doesn't typically go 'bad' per se, but rather begins to leak HV the older it gets. Thus you won't typically have a direct short in the filament windings (which usually results in an audible hiss and the smell of ozone), but you will sometimes have quite a lot of leakage which tends to drag down the power supply wholesale. Remember that any current lost in the HV circuit is also current which is unavailable to drive the CRT, which is one reason I pay so much attention to the horizontal section. The other being unobtanium flybacks.

This problem is exacerbated by the attractive properties of HV, leading to the accumulation of potentially conductive dust and in turn more leakage. The cure for this is of course cleaning, but if you're gonna go that far you may as well just restring it anyway. I keep a spool of Belden 40kv stuff around for precisely this purpose. Don't forget to look for tin whiskers on the HV tube sockets either, those took my Hoffman out of service for a little bit and the length of them can be really surprising. If you see any, clean with fine grit sandpaper. A rag will just move them around, and they really need to be broken up to be rid of them. Protect bare metal from corrosion with WD-40, or other light water displacing oil. Do not paint!

Your problem happened all of the sudden though, which makes me think a doorknob failed on you.

Let's get systematic about this: Set the chassis up so that you can read horizontal cathode current, and take a reading with the whole circuit in play. Next see what happens if you pull V24 and V25, if cathode current is in a more or less normal range and you have good focus voltage, reinstall V24 and see what happens. Isolate the problem by process of elimination. You should expect to see a slight bump in cathode current with each tube that is reinstalled because of the heater, but if it jumps significantly it may point to a problem.

Don't forget to rule out the CRT either, if it suddenly went gassy it would cause these problems. I hope not, but something to look for. Your shunt tube grid circuit is another area to investigate, the 6BK4 will drag HV down real fast if something went wonky with it. Could be tin whiskers in the HV pot as well, just gotta get to eleiminating each part in turn.
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Last edited by miniman82; 12-07-2018 at 01:40 PM.
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  #57  
Old 12-07-2018, 11:10 PM
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Tonight I checked cathode current with V24/V25 out of circuit & saw no significant change. I disconnected the 68mmf caps previously mentioned and saw a noticeable boost in hv, maybe 1-2kv. Pulling the cap off the 6BK4 didn'[t change the HV. Next I'm going to sub another pot for the HV reg control. In-circuit it measured fine but I know that can lie. 2 things are pointing me in that direction: under some circumstances I can adjust the HV with it to a certain point but after roughly the halfway point there is no further increase. Then there was the fact that I was adjusting that pot when things went south. There are no signs of trouble from the pot by looking at it.

One thing i know-that horiz limiting coil is really putting off some heat! Anyway...excellent advice, miniman. Just the kind of stuff I'm looking for.
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  #58  
Old 12-08-2018, 08:56 PM
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Quote:
Originally Posted by bgadow View Post
1) The doorknobs. I had an early b/w set with a bad doorknob once
Yeah, not a high-failure item, but I ran across a bad doorknob cap while restoring my Dumont RA-102:

https://antiqueradio.org/DuMontRA-10...n.htm#doorknob

At first, the doorknob created subtle horizontal blips -- maybe leaking a little -- and then it failed dramatically.

Phil Nelson
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  #59  
Old 12-08-2018, 09:44 PM
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Hot coil implies dissipation- power should not be dissipated in the linearity coil. Switch from reading HOT cathode current to reading total input power to the horizontal circuit- put your ammeter where the fuse normally is and see what you get. Power is going somewhere it’s not supposed to go, either you lost drive or something is shorted somewhere. Either way you have to track it down before you burn something out, I don’t think you’ll find a LIN coil for this thing if it goes bad...
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