The sams with the pictorials also makes it easy to verify you have the right value on those black color band caps.

Well, my "by Christmas" goal will not come to pass.:no: I finally plugged it in. First with a 100watt bulb in the line for about one hour. Everything seemed OK. The light slowly dimmed, so I knew my SUPER SHORT days were over. The bad thing about the bulb method is that the voltage is so reduced that the DC never gets pumping enough (or at all?) to slow charge and reform the paper caps. I think it works this way.:scratch2:

Needless to say after a couple minutes of operation with no sound or raster I heard a sizzle:tears:and quickly disconnected the line.:sigh: Low and behold one of those stupid black stripped paper caps had gotten hot. A .018mfd 1000v damper filter. I unsoldered one end of the thing and it measured like .15mfd.:no: So until I get my hands on the 7 or 8 1000v caps that I will purchase to cover everything needed I am at a standstill. I have enough orange drops to keep me busy with the soldering iron. Just no 1000v jobs.

I feel good even though I still have a dead set. I started off with something that could not safely even be plugged in. I may not be as far away from success as it seems. This cap is probably why I never got a raster. Then I can look into getting sound. I didnt expect a much better result. I just wanted to make sure that there were no screw ups with the power supply re-vamp.

IF you get those caps in time, you could set a new goal of "by New Year's" and possibly have a good enough picture to watch the ball drop for 2007. :yes:

...

Correct. When you "warm start" a piece of tube equipment by variac or series light bulbs, the transformer is operated at reduced voltages. This means the 5V supply to the 5U4 filament is reduced as well. At reduced voltages (especially at the low end of the variac sequence), the 5U4 filament isn't hot enough to "boil" any electrons, the electron cloud is not present, the plates do not conduct at all (no emission). You'll measure little or no B+ until a significant percentage of "full throttle" is reached. I believe it's just a threshhold where, when reached, the 5U4 suddenly fires and a sudden, near-full jolt goes to your vintage caps. This is why most in-circuit "reform" attempts fail.

Build a couple of these (see photo). It is a solid-state 5U4 that uses a pair of 1N5408 diodes as the rectification method. They work at all AC input voltages from 0 to 1000, incrementally and/or smoothly, to avoid this problem.

You'll want to have two of them in your toolbox, one I call left-handed and one I call right-handed. The unbanded side of the diodes go to pins 4 and 6 of the tube base (salvaged from bad metal radio tubes such as 12SA7). The banded side of the diodes, connect together, then connect the joint to pin 2 for a left-handed unit, or pin 8 for a right-handed unit.

It will be up to your specific application as to which unit to use. Either pin 8 or pin 2 will be connected to your B+ supply and power filters. The other will go thru the 5V windings of the power transformer. I don't know that it matters if the high(er) voltage runs thru the 5V windings or not, but I prefer not to do so. So use the unit that corresponds to the pin going to your power filters (i.e. a choke or the 1st electrolytic). 5U4 pins 2 and 8 are symmetrically interchangeable in practice, so don't necessarily trust the Sams schematic. Look at the wiring. I have at least one example where the sams is wrong (my 1949 Magnavox).

This all having been said, I agree that reforming 50-year-old can caps is a risky business. I just use the solid-state 5U4's for slow-starting to avoid smoke-and-flames until I'm sure everything's wired up correctly. After putting in new capacitors.

Somewhere here I read about what the deal is with the 500mfd 15,000 volt cap. It is the HV Filter. I guess I'm wondering if it is more like a ceramic and likely is not bad due to age like the paper caps. Also if it needs replacing I wonder what the trick is to finding a replacemet for that thing. Those are some really large values and I have never seen anything like that for sale at State Electronics (local store).

It looks as if RCA made it easily replacable on purpose. Maybe it was expected to be a weak link that turned out to be really reliable. Who knows? Maybe I'll do a search on the thread concerning this.

Its funny how this whole cap thing works. I tend to be stubborn because I have seen many radios dating back to the thirties that do fine with all or nearly all original caps. Then there is my beloved 56 Philco TV that will and always has come to life like the day it was built. I have a neat Sparton that is the same. There is one difference thought. I bought these sets back in the early 80's as second hand, daily users. Thus they have never been idle for more than 3 or 4 years straight during their life with me. Also I know that at least the Sparton was regularly used by the previous owner. An older gentleman would watch that thing all day on the weekends at an indoor flea market when I was a kid.

I feel blessed in a way to be at least old enough (37) to remember some of these sets still in regular use. The TV repair shops were full of them (junk) and the Goodwill always had a good deal on a nice old black and white, 50's set that someone finally discarded in favor of color. I have had kids come in my house who can not even identify an old set as a television set. They will ask what it is...can you believe it?

Anyway, my point is that the sets that have been idle for say 30 years are going to be very different to revive and can't be compared to something that has been at least in periodic use through the years.

My RCA has several of what look to be factory tubes which tells me that the set may have not been used a WHOLE lot. However, the CRT is a replacement, so it WAS used enough to burn up one CRT. On a guess by just looking at the replaced tubes that the set was not serviced after the sixties. It could have been idle for 40 years.

The HV filter cap is a ceramic type and is not too likely to be bad...it is 500 mmfd (micro-microfarads, or picofarads) not 500 mfd.
Here is a source I have found of these type caps:
http://www.rfparts.com/caps_ceramicdoor.html
If you search for "doorknob capacitors" you will probably find others too.

Regular use does seem to help old electrolytics stay in better shape...I would still replace them myself but if you are going to keep them in it would be a good idea to use an ESR meter and/or capacitance meter after the caps are properly discharged to evaluate the status of the caps, as they do continue to degrade over time.

I highly disagree on both use of solid state rectifiers, and the point of when tube starts conducting. I find that it averages, with a known good rectifier, that it starts producing a low voltage at about 35 volts input on variac.
By 50 volts, you are surging at over 140 volts dc. Mind you, that's surge. As set warms up, this voltage quickly drops. By 85 volats on variac, you are putting out over 200-250 volts dc. At full line voltage, you should get the full dc rated voltage. Note: Back then, the full rated voltage was 117 voolts AC. At least here, in Fl. today's line voltage averages around 124 volts ac.

Further notes, According to John Foltsom to get the correct dc voltages, negative lead of your meter must be connected to chassis.Not to the negative supply lead. RCA was putting in a negative bias supply on this series of chassis. That is why you find the positive terminal of one filter connected to chassis.

Further warning: Remove the black caps going from both sides of line to chassis, as well. You can put in new ones if you wish. I believe the original value on these earlier sets was .01 600volts dc. I personally leave that, and the sometimes installed 270K resistor out of circuit. These two caps were line filters intended to filter out car engine generator noise, medical devices, etc. I find that leaving these two caps out has had NO detrimental affect on the operation of the set. In Fact, with out them, the set is electrically slightly safer on the chassis, making it less of a shock hazzard. Mind you, I'm not saying NO Shock hazzard. I'm saying less.

Please take every precaution on measuring voltages, and handling this set. I'd reccommend one hand behind your back, use clip leads for positive connection, and, have your shoes, and socks on. A rubber matt can also add further protection.

:yes: :yes: :thmbsp: Bill Cahill

This is what I love about AudioKarma. Lots of real knowledgeable, and kind folks.
I forgot to note the footnote on the Sams capacitor list for my set. The cap is ceramic (which I didnt know) and it plainly says that Electrolytic and Paper Capacitors are rated in mfd. and ceramic and mica are listed in mmfd. Thanks Chad! If I were not straightened out on this I may have spent a lot of time looking for something that would be wrong.

This has been a real informative thread and hopefully will help others in the future. However, sometimes we get into debates on particular things and its hard to really know what is correct. Like the question of weather or not a tube rectifier is producing DC at 50 volts. If not, well my theory is right, and you are not doing anything but the power supply filters any good as far as a "slow warm" goes. The tube is not conducting, so you are not getting DC to any of the paper caps. If the other theory is right then the tube is conducting at reduced voltage we do not need to build a solid state rectifier in order to try slow warming. Hopefully this thread will go on to a conclusion on this matter. All old TV people NEED to know this.

This is not a complaint. I love the debate. It helps to better understand what is going on. Without some debate I doubt the learning process would be as effective as I think it is. Great stuff!! :thmbsp:

Bill -

I'll trust your experience. My Capehart was my first TV restoration (after about 50 radios from circa 1935 to 1950). The mentor who walked me thru the restoration was a lifer TV repairman, and he made me build the Solid-State rectifier for the project. For our capacitor re-form experiment, instead of using a variac, we used a Lionel train transformer, and for the first six or eight hours the line-input voltage was less than ten volts. The first half-hour or so, the measured voltages at the positive-side of the filter caps being under a volt. The output of the 5V transformer secondary at that point would have been something less than half a volt. I don't believe a 5U4 vacuum tube will conduct at all under those circumstances. My understanding is that a very vintage cap, to be reformed, needs to be handled very delicately at first, and the Solid-state rectifier was the proper solution. But I'm new to the game and will happily admit being wrong, if wrong, and hope I didn't misadvise anyone. Thanks for your input.

- Kirk

Tubejunke -

Sorry if we got off on the wrong foot again. I agree we need consensus. Are you saying you think the paper caps need to be brought up slowly too? I've only understood re-forming to apply to electrolytics. Please clarify, and others please add consensus-building comments. Thanks.

- Kirk

When we get an old radio/jukebox/amp etc in for repair we don't even try it till all paper caps and electrolytics are replaced. Having repaired and used tube type equipment for 20 years I can say old caps are just bad news.

Using a silicon diode would work for slowly applying voltage to a cap whereas a 5U4 would not: however I would not trust such a cap to work reliably for an extended period. The old electrolyte just dries out. Paper caps are just bad all the way around! They can not be rejuvenated by any means.

Kirk, I think you get me wrong. No "wrong foot" at all. There really shouldnt be one as long as we are all use tact. I was describing the beauty of the debate with no punn or sarcasm. Again I think it is benificial to those of us climbing the ladder of learning things that they don't teach in school anymore. I am one of those people. Always learning. When that stops I will probably lose interest...I have seen debates where there never is a conclusion, so I was hoping to sort that out. I think we have.

Plus we have learned a neat new experiment that we can try in building solid state rectifiers. Save your old octal tube bases when they go bad. I think you could use them for mounting the diodes and a resistor.

About caps, I thought that the Electrolytics and Paper caps were similar in operation. I also thought that the whole theory of "slow warm" was to slowly charge all of the caps as opposed to throwing a shock to a very dormant system.

I think if we knew for sure that a rectifier tube is in fact conducting at say 70vac on the plates and 2.5 volts on the heater. That is what should be going on with the 100 watt bulb in the line. The power to the transformer is reduced to around half of line voltage. I have not taken a measurement but everything is proportional. (I was told half) If you cut the line voltage in half, everything else will be cut in half, such as the power transformer scondary output to the rectifier.

So, if Bill is right (and my money says he is) then everything is good to go for any of us doing the light bulb slow warm. The 5u4 is conducting at reduced voltage. I guess any of us with a good working set could take some measurements and then we could be more precise. I dont have room to tear apart one of my working sets. I may try to get some measurements from the set this thread is based on. That will only happen when I get more caps......

Any volunteers?

:rant:

I definately can get a 5U4 to conduct at only 30 v AC input on variac. Not alot, but, it will conduct.
Now, as for paper vs electrolytics. Paper is NOT the same, and, I agree that it can NOT be reformed, or rejuved in any way.
I further agree that it it far safer to replace the electrolytics.Evn if you do rejuvenate the old ones, it is not likely to last.

I now understand what you were getting at with the solid state rectifiers. However, they aren't less harmfull to the filters. They put more voltage out even quicker than a tube would be able to do, and can cause more harm, alot quicker.

Hope this helps. Thanks. Bill Cahill :yes:

I agree with Chad, replace, do not try to re-form. I tried re-forming on some filter caps used in a couple of AC/DC radios that I have. They re-formed and sounded ok at first. However, after a short time, the radios begain humming as if they had bad filters-they did. I have not had an issue when I re-placed the filter caps.

I also agree that paper caps are bad news all around and should always be replaced.

Took some voltage readings and this is what I found.
The tv chassis is a admiral 24d1 with one 5u4 on top of the power transformer.
With the variac set to 35 vac the power supply voltage was 6.36 vdc
Variac set to 50 vac the power supply voltage was 41.22 vdc.
Variac set to 100 vac the power supply voltage was 289. vdc
All of the electrolytics and paper caps have been replaced in this chassis.
What I have been finding is the sets I did leave the old working electrolytics in, Go bad when I fire up the set after sitting idle. Elcheapo {me} was trying to save money by not replacing the caps the first time around.

I hang a DVM on b+ and bring up the voltage slowly with a variac, using the B+ as a guide rather than the line voltage.

John

Lots of good info. Thanks all.

My Capehart's restoration effort was mentored by the original owner's son, remotely over the internet from about 800 miles away. An interesting mix of frustration and enthusiasm. The set was put away, almost working, in an upstairs New Jersey home's closet in mint condition in 1970. We had a very strong desire to see his dad's set work without any aftermarket tampering whatsoever, which is one pretty good reason to at least try a re-form. In hindsight I could probably have left it alone and have donated it to a nearby Farnsworth museum as-is (which was sort of the original plan). After replacing all the caps, it ceased to be "pristine", and therefore not so much museumworthy. But it works now and I like it.

Our attempt to re-form may or may not have worked. We brought it up slow to 18VAC with the train transformer, then to 95VAC with the train transformer behind a step-up transformer (I bought a variac later, works ok but it buzzes and smokes uncomfortably, in my opinion). At around 95VAC, that's when a few resistors started smoking and cooking nearby components. At this point I lost my nerve and replaced all the wax capacitors. No longer museum perfect, I did the cans too, discarding the possibly reformed cans without ever testing them for good or not. So the re-form ended up an academic exercise only.

Ok, so I just did a simple test with my Sencore tube tester. I put in a good 5U4 testing 100%. I set the filament voltage knob to 1. The meter stayed at zero, no emission whatsoever. I turned the filament knob to 2V, the needle rose to almost the "?" area indicating a weak but good tube. At the 3V setting the tube reads almost normal emission, about 95% of max. The next setting is "4-5V" and at that point the emission is 100%.

1V at the 5U4 filament would already be (roughly) 20% of full throttle, or, say, 25VAC line voltage in our re-form experiment. At this point the HV windings might be putting out 70 or 80 volts but not showing up at the electrolytics at all.

We know by the tube-test experiment that the 5U4 is conducting very well at 40% (roughly) of full-throttle, so the only question is whether or not it's a smooth rise between 20% and 40%, or a relatively sudden ramp-up. Based on some reading on how Thyratrons and other more exotic tubes "fire", I simply surmised that the cathode ions begin to boil at a specific temperature, and are then pretty much boiling. A yes or no condition. This suggests to me a rapid rise between 20% and 40% could occur. At that point there might be 100V coming out of the high(er) Voltage windings. One could imagine a significant amount of that would hit the electrolytics -- a lot more than the fraction of a volt at which you'd want to start reforming a vintage cap. So my theory is that the commencement of ions boiling in a 5U4, on a TV variac warmup, might zap some fragile can electrolytics, that otherwise might have re-formed ok with a solid-state device. That was the theory presented to me by my mentoring authority, so it was the theory I posited here.

I've read in guitar-amp builder's blogs and forums that you don't want solid-state rectifiers in operational gear, unless the amp has a "standby" setting. Something about wanting the other tubes to warm up concurrently, a cold tube with full B+ gets some exotic damage that shortens its life. But that's hearsay info, so take it for what it's worth. I wouldn't run the SS devices in a good TV on a daily basis.

- kb

I think the only problem with the silicon rectifier substitution is that the voltage drop is a lot less (less than 2 volts compared to 30-50 volts or so for the 5U4) so the DC voltage output will be higher than normal. The 5U4 warms up almost instantly so it also provides DC to the amplifier tubes before they are warmed up so on this aspect there should not be much difference.

Nothing but good news on the TC-127!! The whole power supply/transformer issue is no more. What I have now is a raster with what looks like an out of sync picture TRYING to come in. About 2" of vertical sweep is missing. There is no sound. The worst part is the fact that after about 5 minutes the nice, bright raster starts to lose focus and fade out. Thats when I pull the plug.

I still have several paper caps to replace and check resistors and tubes, so theres a lot of possibilities. ALSO, I forgot that I still had two sections of an old electrolytic in use. One is a power supply filter and the other is an output decoupling capacitor.

I say as I get more and more caps replaced these problems will likely iron themselves out. Really the set is on the edge of success as far as I'm concerned. I started with a smoker/flamer!!!

I'm almost there!! Still no sound at all. Thats getting kind of weird. The tuner is a bit goofy also, so in fooling with that I got a signal. With that I see that the horizontal frequency is way off. When I turn the hold control the raster starts to fade. It seems like there is something weird about the brightness and contrast adjustment as well. One of them kind of makes the picture go out of focus and pull in a shadow. The shadow kind of looks as if you are moving the ion trap.

With the improvement of pulling through a video signal I am still happy. Any advice on the missing sound anyone? Tonight I replaced a .01 black paper cap in the sound section. It measured like .165mfd. I hope THIS tranformer (Audio Output isnt burned up too!!

I strongly suggest that you replace all of the remaining paper capacitors before applying power again. By not doing so you are risking damage to more expensive parts. Leaky paper capacitors (and by now most/all of them are leaky) cause excessive current flow which will burn out tubes, transformers, deflection yokes, etc.