the Sams is very very confusing

https://imgur.com/YseSmi3
those dots mean voltage mesured from 95v line.

https://imgur.com/Ev1QkEu


r56 is 1/2 watt, (or so it says ) here om sams, that is a lot of power to be pulling through that resistor for that line esp when the alt version Volt source R, which is not in this set, is seems, uses 2 watt resistors :/

nothing here seems to make any sense...
there should be a alt high power source for the 95v but not sure what it it.

i spent the night replacing a lot of paper caps, 90% were quite bad, after which i was able to get a full screen raster, but still could not tune in anything...

then I remembered :yikes:

the horrid problems with contacts the drum tuners have, so i opened it and looked...
https://imgur.com/ZhqjAHK
:eek::yuck:
black as night.

so i scrubbed off chan 3 with an eraser, and.
https://imgur.com/Heff2BR

:yippy:

great progress for such a short time!
I still got caps to replace, and I'm sure that there are bad resistors in there too.
but it's going OK so far.

https://imgur.com/fEsFhYK

here it is today

tuner is still giving problems.
works sometimes then stops

this is with direct video input

still have vert lin problems
will prob have to pull all tubes and scrub pins and sockets.
and replace even the caps that were replaced before, and not assume that they are OK even though they are not paper ( film type ) who knows how long they were in there...
https://i.imgur.com/HrEK6JY.jpg
you can see one of the old replaced caps in the top left. although, it could also be resistors causing the problem.

vert linearity looking much better.
https://imgur.com/gcteUfS

found bad resistors.

https://imgur.com/5c1EP28
r58 r59
way WAY off, they had been replaced before, but are still no good.
had 1/2 watt ones in there, put in 1 watts

https://imgur.com/jduVGCo
REALLY BAD :o

will prob find other very bad resistors too :/

All tubes have green krud on the pins like my FADA did, so I'm guessing the sockets are dirty too, rather than trying to clean the RF/ IF tubes, I will just replace them, they are old enough, example, when I removed the 4th IF, this was not easy because the tube shield was rusted on, ALL of them are rusty :( , the tube under was an original stromberg carlson tube ( 6cb6 ) though I could not find any trace of that number on the tube, I don't know if it came off, or if was never on or what :o

I'm still debating on taking apart the tuner to try t clean it, the SAMS clearly shows a pic with the drum removed , showing the contacts, but I'm not sure how it comes out, if it comes out w/o much trouble, then it would make easy access to the contacts for cleaning.

I always took out 3-4 of the individual strips and that was enough to gain access to the stationary contacts. No need to remove the whole drum.

Yes, I see that now, I just found a site that shows that they can be removed for cleaning.
https://www.rfcafe.com/references/po...march-1967.htm

This is my first time ever trying to clean this type of tuner, have seen mostly rotary switch type before.
Though the contacts ARE dirty and black in this tuner, I'm still not sure what is going on with the front end, by video injection, I have proven that all after video detector diode is OK and stable but tuner input is intermittent, which may or may not be due to contacts or dirty tube pins, (new clean tubes on the way) , or, it could also be out of tol resistors in the tuner/IF/AFC area.
Not really sure at this point, will have to see how it behaves with known good clean tubes in and cleaned sockets.
How it is behaving is a bit unusual something I have not seen before anyway, when the front end works, it works rather well, stable and solid for quite some time, but when it acts up, the screen goes to a blank raster, but only if it's being fed a signal on a given channel (rf mod into 3) , if I change away from chan 3, or shut off the rf modulator, the screen goes to snow, and back to raster when turned back on.
AGC problem? Noise cancel error? Flaky video detector? Or just a weird symptom contact problems perhaps?

this may be what I have been looking for!
https://imgur.com/1NfY1AN

not on the 12BY7 video output tube, but on the 12AU7 sync phase inv,
it has the 1w 3.9k resistors on the plate and cathode, and is most likely the source of the 95v in this version of the set, which I have been looking and looking for, so I could replace those resistors to stabilize the 95v line. :o

Look at the revised circuit in the SAMS which you show in your last post. In the revised circuit the 12AU7 isn't even connected to the 95V line. R96 goes to ground, not the 95V bus in the revised circuit. The voltage dropping function is typically handled by the audio output tube.

that's what i dislike about this SAMS. you do not know what is really in this set until you track it down.
i did a quick look, and the cathode is indeed tied to the 95v line and not ground in this set.
https://imgur.com/mVtjfmc

that being the white wire...
r96 checked as 4.7k in circuit, i got to replace both! :(

the voltage divider you mention on the audio output is on another version of the set, tied to a 110v line, and can be seen in sams 0258-13n.pdf , the one for this set is, 0314_11n.pdf


I'm really not sure why they chose to create the 95v in such an odd way in this version :o

I'm defiantly going have to go go over this set for bad resistors, I tried again to bring in a signal in the tuner and it was still unstable, worked sometimes, and then blanking out to raster again, but only when there is RF input, 95v line is also unstable at this point, dropping to 82v when there is a pic locked in, and when it seems IF section collapses, it goes up to 109v, then when I remove the RF input, and the snow comes back to the screen, it goes back up to 95v.

And no sound at all from RF input.

But oddly enough, with direct AV input, the 95v is stable, and the picture is fine for a long time, I have had it on for 40 min or more.

https://www.youtube.com/watch?v=L7ypgEFao8s

the speaker was also moisture damaged so it also hardly works.

I'm sure I will find a lot of bad resistors :(

I think i may have found the problem.... and it's not good... :thumbsdn::no::tears:

https://i.imgur.com/lIhTLGp.jpg ( ignore my finger in the pic again :O )

after looking around for bad resistors , and finding just a few.
I poked around some caps...
there are many of these 3 leggers in the IF section.

they SHOULD be 4000pf, but the 3 i checked were at 5.0 5.1 5.2 and leaky at low voltage. they are rated at 400, I don't have the means to test them at 400 :(
seems to me that this will throw the IF all out of wack.

now I am debating, replace them and most likely face IF alignment? or stick with AV input?

Apparently, this TV is getting weirder and weirder, for it seems that the 95v line is not sourced from just v15 12AU7 or v8 12BY7 , but both... to me this just seems very problematic, and just asking for trouble to happen sooner or later, and have no idea why the hell they would do it like this, because it just seems like they are begging for things to fluctuate and oscillate, which is basically what I am seeing when I try to use RF input.

with v15 removed, 95v line drops to 82v , and with v8 removed, 95v line drops to 60v, with both removed, it's 13v.

Symptoms
direct a/v input,
95v line stable, picture is stable, no jitter or sync problems horz or vert.

RF input, tuned,
95v line unstable, fluctuating, 95v with video on screen or snow, over 100+ when IF fails to blank raster with rf input, horz & vert freq fluctuating, and horz & vert waviness seen in video on screen ( not seen at all with direct input )

Suspect bad caps in IF section may be causing problem, should be 4000pf but most testing over 5k (tried more than 1 tester, same result)
however, the original dual caps can't be found, nor can new 4000pf, but 3900pf seem to be all over the place, so I will guess they will be the ones to try, esp since 810-FG24C0G2W392JNT6 are much higher tol and more stable than what was in there in the first place.

It's actually not that uncommon a power supply design. Every design needs multiple voltages. Typically the main B+ for the tuner, horizontal and audio output stages, Boosted B+ for the vertical output and a lower B+ for the IF.

You have a few choices for the lower B+, power resistor voltage divider, separate secondary power transformer winding, rectifier and filter or do what this design did. Use tubes as voltage dividers. I really don't think the fluctuation is any big deal. It's going to vary as the tubes draw more or less current in response to the incoming signal.

Tube circuits are designed with a wide tolerance. I wouldn't be concerning if readings differ +/- 20% from what the service info shows.

Those caps are ceramic and very reliable. I'd be surprised if they are bad. 3,900 is more than close enough. They are just RF bypass caps.

If you want to hurt your brain some more try to wrap it around the Motorola VT-71s voltage divider. They basically had 2 voltage rails and the lower was basically many different stages (the majority of the set) in series/parallel all collectively acting as a B+ voltage divider. It did its job well though.

I'm still a bit stumped by the odd behavior of rf input vs direct video feed, and the way when there IS video via rf in, its very unstable and wavy on the screen and 95v is all over the place.

Granted, all the IF tubes are original and I have new ( tested good ) ones on the way, also the AGC KEYING, and tuner tubes, I also intend to replace cathode and plate resistors on both source tubes for the 95v line, not done it yet. Right now, there is only 1 filter electrolytic capacitor on the line , as original design, 40uf, I may add another 5uf in there.

What would be really helpful is to use a 1077 B&K TV Analyst (or equivalent) and inject an IF signal directly after the tuner. Note the stability of the picture and the 95V bus reading. That would tell you whether the problem is in the tuner or in the IF section of the set. A problem in the AGC can also cause a TV to shut down as you have described.

BAnderson is right. These ceramic caps rarely fail. They are typically used for bypass and therefore their value is not critical. No IF alignment should be required after you replace them.

I intend to re-do the AGC KEYING area as well, especially C54, the .001 1kv that carries horz pulse to the AGC circuit from the fbt, even though it looks like it was replaced before, I do not trust it, this set spent countless years in a damp dirty barn, it had rust, cobwebs and roach castings in it, so far, 95% of every cap paper/ electrolytic, even some film ones replaced before, have been bad, but luckily it seems that only 10 to 15% of resistors are bad, mostly 1watt and above.

To give an example, at first, some of the pots were so rusty, that they would not turn before being sprayed down with deoxit before I could get them to turn :o

I have the 3900pf npo 5% caps ordered, should be here tomorrow, prob won't hurt much just to replace the bypass caps, & the “new” tubes mentioned are already on the way.
Will just have to see how it behaves.

Replaced a few more marginal parts last night, caps / resistors, found that the dual pot R9 for AGC/NOISE CANCEL is in sad shape, even after taking it apart and cleaning, replacing it is proving very hard, because, where as dual concentric 500K audio taper pots seem to be very easy to find all over the place, linear taper ones are about as easy to find as a goldfish in a desert at high noon.
Dare I use audio taper?

Most tubes ordered will be arriving today, so I will be able to try will known good (tested ) RF/IF tubes soon.

Audio tapers are logarithmic. They will work, but the adjustment will not be uniform like a linear taper. The adjustment range of the audio taper will be "bunched" at one end.

I think it's Mark Oppat who has the parts to recreate most vintage radio potentiometers.

If you're feeling adventurous you could try finding a new dual audio taper pot mechanically identical to individual linear pots from the same maker and swap the resistance elements between the three.

There is yet another option,
https://i.imgur.com/VwqCuEK.jpg

You can see just how ugly that pot looked before I tried to clean it. :(
There is no reason both adjustments MUST be on the same shaft, the HOR LIN , option is not installed in this set, so, if I can't get the original pot to behave, and find a suitable dual concentric replacement that's linear, I can just split it and put it in 2 locations.

Another thing I have noticed while poking around under this thing, the yolk has been replaced before, splices in all 4 wires underside.

IF tubes replaced, new bypass caps, and new AGC tube,

https://i.imgur.com/Zipl6L3.jpg

now much more stable with RF input, but still has a tenancy to oscillate on the 95v line, gonna add one more electrolytic cap.

sound was still weak, after replacing the old caps in the sound area, did find a bad 86 ohm resistor on the plate of the audio output,( checked at 105 ohm ) that did help a bit, but still not very loud, it may just be the crappy speaker.

I WILL have to change the AGC pot, It's unstable.

To clarify, what I mean by oscillation is, some weird harmonics in the 95v line, that tend to show with RF input as unstable picture and sync, it can be fine for some time and then just go nuts, and I can get it to stop by briefly shutting off the RF modulator and turning it back on.

As mentioned before, the source for 95v is a bit odd in this set, v8 & v15 with one filter c2b.
https://i.imgur.com/YseSmi3.jpg

C2 b 40uf the only filter on the 95v line, is on the front of chassis, focus socket is at the back, (95v is being used,)
v8 1/2 the source of 95v is on the left side, v15 the other half is on the right.
I'm hoping that adding another filter cap at the focus socket may help things run more stable.

For the most part, when tuned in and NOT oscillating, it has a pretty good picture for it's age.

Well, video via RF input is now pretty stable and OK, but I have not been able to get sound to work, still very quiet.

It is NOT the tubes, and I have been through the whole area and replaced every resistor that was less than 10% what should be, but it still is very weak sounding, tried tweaking the sound IF, that was no help.

https://i.imgur.com/c1mGoQR.png

been all over it , voltages are OK, but poor sound.
i suspect the cap hidden in L24 may be causing a problem.

a new coil can be gotten but at this point I feel it's not worth the trouble, esp since there is a easy way to feed audio into this set via an RCA input and would only take re-wiring a switch.
https://www.youtube.com/watch?v=6puItmZnQsk

this is with RF input and direct audio, ( faulty audio IF bypassed ) and a decent speaker! sounds great!

keep in mind, I have not put on the centering magnets yet, so the final screen adjustments are not done.

I am assuming this has to be a mistake...

https://i.imgur.com/sdXG704.png

VTVM to point D, common to chassis, input 4.5mhz at point C, adjust input till 1.5 volts is read, keep there for the remainder... BUT UM...

https://i.imgur.com/c1mGoQR.png

POINT D HAS A - VOLTAGE ON IT!
and is tied to a negative side of an electrolytic cap.
so, should that be, adjust generator output until -1.5 volts is seen at point D?

THEN adjust for max defection?
confusing...

Looks like a mistake to me. I would say if you connect the VTVM reversed of what they say, that should give you a positive reading. If you look at the diode conduction, it seems like the voltage at point C [EDI T - oops, point D] must be negative compared to chassis.

Then tune A11, A12, A13 for maximum while reducing the input level to keep the reading near 1.5 volts.

I may be succumbing to another geriatric grand mal brain fart:eek: since this has been over 50 years ago. But the few times I've replaced that small electrolytic in a ratio detector, the cap was always 'upside down' with the positive end to ground.

Um.. don't you mean point D? Going by direction of conduction >, the diode is gonna put an excess of electrons (negative voltage) on pt. D

Compare to diode direction if pt. D were positive.

Again, I may be all wet, so all bets are off.

Sorry for the typo, yes, point D should be negative. I don't even see point C (the input) on that clip of the schematic.

point C is tied to the far side of that 5pf cap, (c58) and goes directly to the video detector diode, before any peaking coils.
https://i.imgur.com/goeH862.jpg

I am seeing barely perceptible contrast smear on bright objects on the screen, (to the left/right ) this is seen with both RF and direct video input, not sure if this is a sign of a real problem or not, or if this is just the standard for a set this old.

looking better

replaced a peaking coil
https://youtu.be/rDpXewiOVNM

RF audio now working after new L24 coil ratio det.
Speakers that were with the set are shot, not sure what I can replace them wit, I just may use a big ext one.

:thmbsp:

Where in the world did you find the peaking coil (L24)?

Talon had it.

https://talonelectronics.com/shop/item.aspx?itemid=7720

they have a lot of hard to get parts.

It's blatantly obvious the the original yolk had a … problem and needed to be replaced, it seems to have failed rater violently, it's no wonder it did not take the CRT with it.
https://i.imgur.com/zzpbKHC.jpg
it says in the Sams to use the back of the original yolk with the centering magnets on the new yolk, which seems to be what was done, but it was so damaged, I do not think I can ever get it back on again.
The damn thing is melted to death!

I may be able to bodge some of the rings from my projector tubes on to it, don't know how well it will work , or somehow use the plastic from the projector assy with these old rusty rings, somehow...

who knows.

Your problem with the centering rings is very common. The plastic used could not withstand the repeated heat-cool cycles. There have been many posts about making a new yoke back end to accommodate the centering rings.

*yoke

All the plastic on the yokes do that over time, nothing violent about it. Bob Andersen has a couple videos showing how to rebuild them. One he did out of some PVC and as I recall the other from a yogurt container.