My Christmas day 9T246 restoration! Almost.....
 

Decided to have a go at my 9T246 that's been "on display" since I picked it up over the summer. Powered it up on a variac when I got it, and while the raster was bright, the picture was a distorted mess. Today, as the wife was baking cookies, I went as far as the capacitors I had on the shelf would take me, and this is what I got!

Clicking the picture will take you to the video :)

http://i44.photobucket.com/albums/f9...h_100_2418.jpg

Weird problem though. If I leave it on the channel that was on when I turned it on, the set is fine. As soon as I change the channel, the picture loses horizontal sync. Otherwise, I just watched a full episode of Gunsmoke on the thing.....

If I turn the set off for a half hour or so, then turn it on, the channel I left it on is fine.

Ideas/thoughts? Obviously I'm going to have to order the rest of the capacitors and finish the re-cap, but this is something I haven't seen before.

Dah-Yum, Tim, for just "Foolin' Around" that's pretty dad-blame good..

I got lucky :para: :D

Yeah, maybe so, but you're also pretty GOOD, too...

there is a rather involved setup of the sync, adj the horz coil top and bottom, then the sync drive cap. Clearly you need to to all the caps and would be a good idea to replace the domino style caps in the horz circuit as well.

You are also living dangerously with original electrolytics, and, those black beauty striped capacitors. I've seen them explode.
I've seen electrolytics explode, and, do other nasty things. I had one in a 9T246 that actually shorted to another section. Result. smoke for an angry resistor, and, the set still lit picture tube, but, lost all reception, and, I couldn't turn down brightness control. That circut was shorted when the cap shorted to another section.
If a filter blows, yo'll blow your resistor bank on the back of the chassis. Then what will you do??
Bill Cahill

Good Job Tim, you're on your way to working history. Lets see more.

That's looking pretty good.:thmbsp: There's a good chance that replacing the rest of the caps will help the sync lock in better, then make the horizontal waveform adjustments as Dave mentions.

Yup. And make sure you replace the molded paper caps along with all the tubulars and electrolytics.

I would also replace the silver micas in the horizontal sweep section, as those seem to be failing nowadays.

Then, check the tubes and high value resistors, and tweak the set with a Test Pattern.:smoke:

http://i268.photobucket.com/albums/j...ssembly018.jpg

So, basically, I just need to finish the job :) . Kinda figured that was the case, it's just that I've never seen something like that happen before. Left on channel, I had it playing for about a half hour with no issues. Change the channel at any point, and all of a sudden, bye bye horizontal sync.

Time to order capacitors :)

I am still amazed that everyone in this forum insists on always replacing the electrolytics. The original electrolytics used in the RCA sets of the period will probably outlast the ones being stuffed into the cans!

It is a simple process reforming the dielectric and testing the things. I have replaced some electrolytics if they do not reform properly. The test is to ensure the leakage current remains below 100uA at full rated voltage.

Paper capacitors do leak and need to be replaced. When I get a set and before powering it up, I will test a few of the paper capacitors. If any show leakage (as they generally will) I will replace all of the. However, the electrolytics and micas are generally okay.

Hmmmm....No. I disagree.

You can get 105 centigrade rated electrolytic caps from Mouser that are light years ahead of anything they made in 1946. Cheap money, too.

Were the 'lytics that RCA used in '46 good? You bet. Are they any good now? Do you really want to roll the dice and worry about it? Plus, the micas in the hor sweep circuits are starting to fail. I habitually replace those now, too.:smoke:

http://i268.photobucket.com/albums/j...inished003.jpg

http://i268.photobucket.com/albums/j...edto25K002.jpg

Have you ever cut any of them open?
Most electrolytic caps from 1950 and earlier that I restuffed were dried out and crumbling, the foil was deteriorated and rotted not to mention the leakage between sections.

Occasionally I will find some that still work but knowing what they probably look like inside there's no way I'd feel comfortable using them.

Yah, the innards of 1940s electrolytics are usually nasty. The photo shows a can from my 1948 Capehart-Farnsworth 661-P.

That one came out mostly in one piece. Some come out with a bunch of dust and crumbly chunks.

I don't care if anyone else replaces electrolytics -- it's your TV, do what you like -- but I'm not comfortable running with that kind of component onboard.

Phil Nelson

http://www.antiqueradio.org/art/Cape...1-PPart912.jpg

Yikes! Did I read what I think I read? Sorry, I have to respectfully disagree with this as others have...

Double Yikes!!:eek::jawdrop: I read it too, and dunno what to say. So I guess just don't say nuthin'.

I'm gonna go through and replace them. That was my intention from the beginning. Leaving them alone is okay if you want to just off the set as "working", but if you want to actually USE the set, you might as well just leave the chassis sitting on the bench, because chances are they're gonna fail anyway.

Parts are on order :)

Horizontal sync that locks as the set warms up, but won't relock after a channel change is a relatively common problem on the early RCA sets using this and similar horizontal circuits.

The cause is misadjustment of the multiple controls in horizontal sync.

I don't have a factory schematic on this set, so take look at the Sams 74, fol 8:

http://www.earlytelevision.org/pdf/R...-Sams-74-8.pdf

If the .01 Mfd cap on the exposed end of T3 Horizontal Oscillator coil under the chassis is original, you can bet that this set was taken out of service before it was 10 years old. But, you say, this cap is paralleled by a 22K resistor, how could a little leakage hurt? Well it can cause some well-intended person to mess up the other horizontal sync adjustments!

After you have finished recapping the set, follow the alignment procedure on page 18 of that Sams. If you are lucky, you won't have to use a scope.

But if you have (or can borrow) a scope with a low cap probe, and you make the final adjustment and then repeat the full page 18 procedure to even things up, you will find that these early RCA sets were some of the most stable sweep sets made during that era.

Today we take for granted that the TV signal will be stable. Remember when this set was made, when ever the station switched from network to local, there was a slight time-shift in the sync. On the smaller stations, often the film chain would also be slightly off with the studio cameras, and location footage would be even more off. These circuits kept the RCA sets from rolling on scene changes, unlike the sets from many of their competitors.

Re: Mica caps

Try to avoid bending the leads of the old ones. This seems to start problems.


Re: Electrolytic caps

If you decide to keep the original electrolytics, add fuses ahead of them to kill the power when they fail.

I won't join the argument on replacing electrolytics, but I am more inclined to leave a pre-1960 one in for set testing (only after disconnecting it and reforming) than a post-1970 one in any circuit. Either way, restuff or replace, carries a definite risk unless you can find relatively new industrial or military grade electrolytics. I am unimpressed by the quality of currently available electrolytics for tube-era voltages. They seem to be made to last the length of the warranty.

James

James, thanks a TON for that useful information. The project will resume as soon as the parts arrive :) .

For the capacitors, this is what I plan to do. I did this work on a '52 Motorola as seen in this picture. While it won't be popular to the purist, I intend to use the snot out of this set when I'm done, and to me, serviceability is the key. I have no intention of restuffing them, and letting loose caps dangle on the underside isn't really appealing......there's no real room to do an under-chassis mount in these areas.

http://i44.photobucket.com/albums/f9...d/100_5093.jpg

Another shot of the '52 Motorola. See how it cleaned things up under the chassis?

http://i44.photobucket.com/albums/f9...d/100_5094.jpg

Thank you for the replies! I respect your disagreements. The philosophy of simply replacing a component because everyone does it seems odd to me. I have seen my share of bad electrolytics. I just want to point out you can easily test and measure whether an electrolytic will hold up and whether it is good or bad.

The test is simple: reform the dielectric and measure the leakage current and capacitance. The reforming of a capacitor takes a few hours and I will put the full rated DC across it for a few days. If the leakage is more than 200uA, then it must be replaced. 200uA is far below the point of creating any heat dissapation from the capacitor. If you detect a 450v capacitor getting warm, then the leakage will more like 10000uA or above.

The RCA set capacitors used from the KCS28 chassis upwards are extremely good. Of the six sets of the late forties and early fifties vintage I have restored over the last 40 years, I have replaced two electrolytics. And the ones replaced never shorted, they became open. I have never had an old electrolytic explode as a result of the precautions I have taken. I have however seen newer capacitors explode.

The measure of pulling one apart and it looking crumbly and bad is no judge of its condition. Dry electrolytics use a dry paste and even a good one will crumble upon taking it apart.

Then again if you feel uncomfortable about this, by all means pull the old capacitor apart and stick in newer replacements. Also, if someone has been foolhardy to plug in the set after it has remained doment for 40 years, then you should expect explosions and fireworks. By my monitoring procedure I will find if a capacitor has been stressed.

I would just like to reitterate that I find it unfortunate that the assumption is that a component must be replaced without even testing the component to see if it is bad.

When I replace electrolytics, I use the good 105 degree C Nichicon and Panasonic caps, and exceed the origional voltage ratings by wide margins. I usually double a 25v rated 'lytic with a 50v, and for 250v I always use 450v, etc.

I like overbuilding these TVs when I restore them. The last thing I want to do is open them up again when I'm finished tweaking them.:smoke:

Amen.

Well that seems weird, for me, the opening of them up is the fun part. :D It's at least way more interesting than changing the oil on the daily driver.

You guys might find this webpage from Illinois Capacitors interesting. It has capacitor Life Calculators for electrolytic, film and ceramic capacitors.

It quantifies the advice we've seen nicely. Voltage derating does indeed increase the life span. Using 105C rate caps extends them considerably more though.

Typical general purpose caps have a 1,000-2,000 hour life at maximum temp and voltage.

Nichicon has a new line out of high ripple, long life caps rated for 450 volts, 105C and 10,000 hours. They also have a very small diameter and great for restuffing cans.
http://www.mouser.com/images/nichicon/lrg/pzcs.jpg

Use one of those at 300 volts, keep the temp down to 50C (122 F) and it should last about 675,000 hours or 77 years of continuous operation :)
Using a cap with the same ratings except 85C should last about 169,706 hours or 19 years of continuous operation.

Well I have owned a set with esentially the same chassis as the 9T246 since 1969. I have since replaced all the paper capacitors, the AGC and sound discriminatorelectrolytics, a few resistors and a number of vacuum tubes since 1969. But all the power electrolytics still function as originally designed.

To each his own. I prefer to keep the sets as original as possible and I can assure you that I do not have to pull the chassis because of electrolytics.

I suggest you prove it for yourself. Take an old electroltyic from a 40's or 50's era RCA TV, reform the dielectric as I suggest and measure the leakage current. You will find that rarely do these capacitors go bad.

And consider this: if after 50 years the above test shows that a capacitor is still good, would this not suggest that the new capacitors that are currently used for replacement, may not last as long?

I have tried it myself on sets from the 40s - many times. Easily 75% are open due to a deteriorated electrolyte and cannot be reformed. I also find many original electrolytics have already been replaced back in the 50s.

But one would have to assume the odds would have been much better had you gotten into the hobby back in 1969. I think the longer they sit idle, the less likely they are to recover.

I've hacksawed off old can electrolytics near the base, the location just above the fat part at the base. That fat part holds a rubber gasket, which holds the terminals down below the chassis, and has wires passing thru to go to the actual cap guts. Clean off the top of this rubber gasket, and then either mount new caps to the terminals below the chassis, or drill small holes to pass new cap leads so you can mount the new caps topside and have the leads connect to the appropriate terminals below. If you're lucky you can slip the empty can over the new caps on the topside. Put one or more caps down below if they don't all fit. One advantage is that you don't have to undo the wiring on the terminals.

since we are talking about caps, I decided to test out reforming a NOS 3 section.

150 @450v
100@400v
100@50v

I started out at 25v, the eye quickly opened, I jumped up to 150 pretty quick and again it opened pretty fast. I have it sitting at 250v now and its about .2ma of leakage (have a DMM in series with the cap eye tester). I will leave it there overnite and jump up to 350v tomorrow and the 450v later in the day.

I will check for leakage between terminals later, and then will leave it alone for a couple of weeks and see how well it performs. I have a big box full of these NOS caps, I had orig planned on using them as base donors but I like to experiment.

I personally do not replace a can cap automatically, like Pentode, I try to reform them out of circuit 1st, if they compare to like new caps I just reconnect them and then fuse the B+

I did a recent project where I did this on a 8t241 chassis, replaced all the wax paper caps and a few of the horz mica (after having some horz issues).

All the cans were reformed and tested fine, some had been replaced some were original.

I am not trying to say its wrong to replace them, but I prefer to do what it takes to get the set running and then trouble shoot issues as required. different strokes for different folks.

I spent a few hours this afternoon trying to reform a dual 40mfd @450 from the 1948 set I'm currently working on. I was able to eliminate leakage but there's another problem I've encountered before. The capacitance is a small fraction of what it should be. I figure the electrolyte has broken down and it's just not doing it's job properly.

So I'm curious - when you guys reform them are you also checking the capacitance and is it within spec ?

yes, and the power factor as well. For the most part the test well over like 50%, if it was under I would reject it outright. I like to compare them to new caps, they generally test higher value, about the same in power factor, and up to about 2 to 4 times the leakage (but its still very low). I used to have a chart that was used for acceptable leakage.

It would not be uncommon for me to take more that 24hrs for one section. Is this really needed, maybe not but it cant hurt to try and besides like I said before it appeals to my interest in experimenting.

What I would really like would be a test setup that I could program to step up the voltage based on current, say have it ramp up to try and maintain a set constant leakage current (selectable), then graph that voltage over time and set the max voltage to end the test. The resulting curves would be fun to examine.

you could do it with a constantly variable DC power supply and a current meter (analog would be easy to watch) but I dont really want to stand by the PS and work that for however long it may take.

all the sections seem to have responded well to reforming. I will set it aside and check it in a couple of weeks.

While I understand the premise behind reforming the electrolytics, if you've got a set that you actually want to watch, isn't it easier in the long run just to replace the stupid things? :dunno:

Just like WA2ISE, I have a box full of removed multi-section cans. A few weeks ago, I tested them on my EICO 950. Almost every one of them had at least one open or leaky section. While the open caps are done for, the others could be reformed. Having never heard of reforming before following VK, I have RCA 721TS and 8T241 that I could try this on when I finally get to them. I also plan to fuse them pretty tightly as well!

For sets that are not what we consider "classics" and most of my 30's radios, I generally leave the old ones in, disconnect and solder new ones under the chassis. If someone has the time to refrom or restuff them in the future. At least they look original from the top.

Now you see 'em...

http://i268.photobucket.com/albums/j...Resto011-2.jpg

Now you don't...:smoke:

http://i268.photobucket.com/albums/j...CSResto012.jpg

To further belabor the reforming of an old electrolytic capacitor discussion :boring:, the reforming takes time, especially if the capacitor has remained dorment.:scratch2:

Last year, when I restored an RCA 9TC275 (1949 with a 16AP4)) according to the original owners, the set had sat in a basement since 1964 un used. This set was a good test case as someone plugged in the set and melted one of the 5U4's literally!!

I was curious if the capacitors could be revitalized after this abuse. I found all the electrolytics almost a dead short. I left in position each electrolytic can on the chassis and isolated the connections to individually test each capacitor. I used my Sprague TO-6 to reform the dielectrics one-by-one. Each electrolytic section took about two to three hours to reform. After replacing all the paper capacitors and a few other components (mostly bad tubes and resistors) I ran the set on the bench for a couple of weeks, keeping an eye on the electrolytics. A 40ufd section of a multi-section capacitor opened and i replaced it with a new old stock multisection unit (after reforming it). I now use the set almost daily and it is reliable without any capacitor issues.:thmbsp:

What must be remembered is that even the dry electrolytics have a healing property. The crumbliness when disassembly is normal and does not necessarily mean the capacitor is bad.

Incidently, I am still working on my CTC5 and it was another long time dorment set with shorted electrolytics which reformed nicely apart from two Canadian Mallorys which was part of the Canadian 25Hz modification. The US RCA original capacitors all restored fine and are healthy with leakage below 100uA at full rated voltage.

I would encourage all to consider at least testing the components before condemning them.

Saying that, I have also done my share of restuffing over the years. My method is to slice the can about half an inch higher than depicted above. That is, about 1/2" above where the can becomes larger in diameter. I then obtain short section of aluminum tube slightly larger in diameter than the electrolytic and cut a 1" length. I then carefully slice it to remove a longitudinal section to reduce its diameter just enough to ensure a force fit on the inner diameter of the old electrolytic tube. I install new internal capacitors and then press fit with a vice the capacitor back together over the prepared 1"section of tube. The result is clean and barely perceptible from the original.

easier... maybe but not by much. I just disconnect the leads and hook up the variable power supply. after that I just walk away and check on it now and then. If they check out I reconnect the wires and its good to go.

I have MANY sets that are daily drivers, examples are my predicta and portacolor, the predicta had one bad can cap, the one with a low volt high value. the other two (a doubler and a mutisecion can that lays down in the back) checked out fine. I use it daily and its fine.

the porta color has its orig caps (1972 IIRC) its on for hours everday and I have had no problems at all with it.

I have a zenith CCII same story, and many sets from the 60's same deal.

I do of course come across bad caps, and when they test bad I replace them, but I do not just wholesale replace, I just dont see the need.

Besides frankly I sometimes wonder if the new caps will last any longer. I am not saying its right or wrong but it works for me.

When I do find a bad one, I use a bone saw, cut the can off at the shoulder, use a pin vice to drill holes from the bottom up, then put tall skinny radial caps in and solder them to the existing can terminals. Takes about 5 min per section so its fast, and I leave the orig lead dress alone. if there is a cardboard cover I will just put the now empty alum can back on and use the sleeve on to hold it, if no sleeve I use a little bit of 5 min epoxy around the edge (after cleaning it up).
The down side is the epoxy is not that strong a joint, so if at some time in the future, someone grabs the can like a handle for the chassis they may be in for a big surprise when it lets go.


after reading Pentodes method of using an expanding internal sleeve I will have to give that a try.

I have tried the uncrimp method, but that just takes a bit more patience than I have. the bone saw while crude is easy and quick.


I promise no more reforming on this thread, I don't want to come across as a zealot.

I threw together what you described above from Radio Shack stuff. It uses an Arduino Uno and a pulse width modulated motor controller to drive two 12.6V to 120V filament transformers to step up to 240VAC. Then a voltage quadrupler. This results in a programmable 6-900 VDC supply, The Arduino software reads the analog inputs to raise the capacitor voltage while limiting the current and max voltage, and then monitoing the current decline to the required minimum current. Anyway, here are some plots from four capacitors. I set the current limit to 5 mA, and the voltage limit to the cap working voltage. The first cap is a 630TS 40uF 450V, the second a Sprague 16uF 450V cap added as a repair, the third a 630TS 80uF 150V cap, and the last a Nichicon 82uF 450V cap. My Sencore LC75 says the RCA caps show a lot of dielectric absorption, the Sprague is toast, and the Nichicon was the best (of course, its new) but did also show some dielectric absorption. I thought it would be interesting to plot the computed power going into the cap as well as its computed effective resistance along with the measured voltage and current. Although its now controlled through USB, it could be standalone with the addition of a small two line LCD panel and some switches. I think I could save some of my 630TS caps, but some are completely unresponsive to reforming.

interesting graphs, would like to see both graph at 200 seconds. for 1 and 4

Also if you reran the test on the old caps does the graph change (reformed) so the low current target at rated voltage is reach sooner.


I looks like the 82uf took that long to hit max voltage, perhaps for reforming you could ramp down the current to say 1ma max. Very neat project.