Beginners guide to Vintage TV Restoration?

[Steve K]

The set that you are starting on has a power transformer and therefore does not have a hot chassis. A set with a hot chassis is one were one side of the power line goes directly to ground.

Steve

[RetroHacker]

As Steve K. said, that set you have has a power transformer - so no hot chassis. But the radio you're starting on (5 tube RCA) is most likely a "hot chassis" set. Let me guess, the five tubes are 35W4, 50C5, 12BE6, 12BA6, 12AV6? In order to save the cost of a power transformer (the single most expensive and heaviest part of a small radio), the radio and tube manufacturers came up with a set of tubes that, when strung in series, equaled roughly the power line voltage - 50+35+12+12+12=121 volts. Close enough to the power line to work well. All the tube heaters draw .15 amps, so in series the voltage drops work out. To generate the B+ the tubes need, they rectified the line voltage with the 35W4, and smoothed it with a couple of electroltyics, yielding something on the order of 150v. It works well, but it also means that the set's "ground" is essentially one side of the power line. And this was in the days before polarized plugs and grounding prongs. You have a 50-50 chance that the chassis will be connected to the "hot" line, so if you were to, say, touch the chassis while leaning on a radiator (grounded), you'd get a nasty shock.

To make matters worse, a lot of the earlier sets (espeically when they were the octal series of tubes - 50L6, 35Z5, etc) had metal screws that connected to the chassis and were exposed on the bottom. In later years, they got creative. The metal chassis was no longer "ground" but connected through a resistor and a capacitor. This works pretty good, and is safe - at least until the cap shorts. In some of the even later sets, the knobs can't even be pulled off the front - the chassis must be pulled out the back, off the knobs. This is because by making it so that the knob can't be pulled off (metal retaining clip inside), the metal shafts can't be exposed, which would potentially be line connected. They didn't care about lost knobs. Only lawsuits.

Now, that doesn't mean these radios are unsafe to use, just be careful and use common sense. And once in the cabinet, the radio will be fine. But when working on it, either use an isolation transformer, or simply be careful to only touch plastic knobs when the radio is plugged in. I always put some knobs (any random junk knob will do, if you're worried about them getting damaged) on the chassis when I'm working on it, regardless of wether it's a hot chassis set or not. It makes it easier to turn the shafts when testing, and of course, on those transformerless sets, it's a safety measure.

And don't be shocked (pun not intended) if you get a tingle from a transformer type TV or radio chassis. There's typically a bypass cap that's connected between the AC line and the chassis to reduce noise. These were originally regular paper type capacitors. When they're bad, they start to leak, and then you get voltage on the chassis. Another reason to replace capacitors.

And you're not going to find the parts you need at Radio Shack. The electrolytics you need are 160 volt rated, and the normal caps you need are at _least_ 200 volt rated. They don't carry stuff like this anymore. You need to go to an electronics store, or order parts online. Justradios.com has a great price on a kit of 240/230 common capacitors (non-electrolytic). It's $70, but the shipping is free, and it's much cheaper in the long run over buying them one at a time. I use these caps and I'm very happy with them. If you get the little yellow ones, be sure to pick up .047's too, they're not in that kit, but you're going to need/want them for five tube sets. They carry electrolytics too.

-Ian

[bgadow]

A quick and usually reliable way to tell if a set is "hot" chassis: look at the tube numbers. If they all (or almost all) start with a 6 then it should be okay. (that means all the tube filaments are wired in parallel) In a hot chassis they are wired in series, like Christmas tree lights, and they will not all be the same voltage (don't ask me to explain why!) You can have tubes starting with all sorts of numbers and if they are jumbled up like that you can bet it's hot. The vast majority of 5 tube radios are hot chassis, known as the All-American Five. Most common used 3-12 volt tubes plus a single 35v and a single 50v. Probably what your RCA is. You just need a little extra respect when working on them while plugged in. (Touch the chassis while warming your feet on the baseboard heat, as I did at age 12, and suddenly YOU will be plugged in! This did not kill me but it also did not encourage me to do it again!)

Oops! I stepped on you a little, Retro!

[RetroHacker]

One more thing I forgot to mention. On your five tube radio, make sure that the pilot lamp is good (if it uses one). If it burns out, then the rectifier tube will be run too hard, and burn out more quickly. The rectifier tube actually has a tapped filament, so that a pilot lamp can be connected to it without needing a dropping resistor. The way some sets are wired, the plate of the rectifier is connected to the lamp tap as well - this makes the light brighter, but if the light burns out, then the rectifier filament at this tap has to bear the extra load of the B+ current. It'll burn out faster. So replace the pilot lamp if it's burned out, or rewire the set so that this isn't going to happen.

Doesn't apply to all radios. But it applies to many.

-Ian

[cdmarion]

In some of the even later sets, the knobs can't even be pulled off the front - the chassis must be pulled out the back, off the knobs.

Thats exactly the way this RCA is built, I couldn't get the tuner knob off until i pulled from the chassis side.

Let me guess, the five tubes are 35W4, 50C5, 12BE6, 12BA6, 12AV6?

Yep

No power transformer, the power cord is connected to 35W4 tube socket and then to the on/off volume control.

You just need a little extra respect when working on them while plugged in. (Touch the chassis while warming your feet on the baseboard heat, as I did at age 12, and suddenly YOU will be plugged in!

I'm glad i asked.

[Dave S]

Originally Posted by RetroHacker

There's only what, like three dozen of us wordwide...

'Bout a hundred of us show up at the Early Television Convention every year!

Originally Posted by Chad Hauris

We have never had any problems with using the old capacitor leads to attach the new one to.

Here's a present-day version of an old radio repair kink: http://tinyurl.com/39jzga

[kbmuri]

Originally Posted by Dave S

Here's a present-day version of an old radio repair link: http://tinyurl.com/39jzga

These are exactly the tight spirals I make. I must have seen an original "quig" sometime in the long-lost past.

Note the comments about "Original Craftsmanship". My point exactly.

Thanks, Dave for the link.

[cdmarion]

My capacitor kit came in from Just Radios yesterday afternoon, and after a couple of hours my first radio project was complete. And guess what??? It worked. Imagine that. It amazed me how much louder and crisp the little RCA became after a re-capping. I've got a few more radios to do and then it's off to the Admiral TV.

[RetroHacker]

Way to go cdmarion! You're well on your way! Glad to hear things are going well. It's really satisfying to spend time replacing components and then have your radio/television work - and work better than it did when you first got it. So, how was the first project? Run into any problems? What kind of set was it - the chassis type or circuit board type?

See - and now you have something to listen to while you work on future projects

-Ian

[cdmarion]

The radio is a RCA model X-551 1952. Everything went great, i had to dig for a couple of paper caps but i just took some pic's and notes to make sure i got things back where they belong.

The only problem i had was when i first turned it on all i got was a low hum and i noticed that tube 12BE6 was not lit, i thought this is great, i get to do some real troubleshooting, i double checked the tube and even replaced it with another and still had the same problem. So i started looking under the chassis and found some solder bridging a couple tube pins, i cleaned the solder off the socket and she fired rite up and the rest is history.
Lesson learned is to be more carefull when desoldering, using the desoldering tool is all about timing and that time i was a little off.

I've been listening to this thing almost non stop and it's doing great.

Next project which i will start on when i'm done with this post is a 1951 Bendix model 526A. This one has a loud hum but distorted audio can be heard. I've got a good idea why the hum and how to fix, i'm looking forward to seeing if i'm rite.

So far i'm having having a ball!! I'll keep you guys posted.

Chris

[bkharris]

Just found the Markus book I mentioned online at http://www.pmillett.com/technical_books_online.htm

There are some other good books there on tubes and equipment ... Enjoy

[cdmarion]

Execellent link!! I downloaded the Markus book. Looks like a great book.

Thanks

[cdmarion]

Ok, i haven't posted in a while. I've been re-capping radios and reading books. Last Sunday I decided to take the plunge and start on a TV. I ended up buying a CRT tester on Ebay and as soon as it got here I started testing crt's in the TV's I've got. I had originally planed on doing an Admiral TV that I bought for $35 but the picture tube tested bad. So I went for my other Admiral, the Tele-Bar. It took me five days working a few hours after work and Saturday. I recapped the TV and radio, tested all tubes, replaced the HV Rectifier tube and fuse and alot of cleaning. I should add that the Tele-Bar was completely dead with exception of the radio when I got it. So I brought it up slowly on the Dim-Bulb Tester.....No smoke or strange smells. Then I took her all the way and guess what.......................It worked (haven't checked the radio yet). I adjusted the picture in with the front controls. It still needs a little tweeking, and the picture seems a little dark but very watchable as is. I haven't put it in the cabinet yet, I plan on doing some cabinet touch-up before I put everything back together.

I could go on and on but I won't. I have to thank everyone in this Forum that helped me. You guys got me started when I didn't know where to start. Really, I couldn't have done it without you guys. Thanks!!

All I can say is THIS IS REALLY COOL!!!

Chris

[M3-SRT8]

Although not recommended, it is possible to begin a restoration hobby by starting with a television. I had never fixed or restored ANY electronic device, ever, before I embarked on a complete electronic & cosmetic resto on a 1947 RCA 630TS.

I didn't know a non-polar cap from an electrolytic before I began, but, with the help of friends on and off line, I learned fast.

The result was a restoration that would stand up to anybody's scrutiny. It can pass for new out of the box, right down to the Labels.

To All Beginners, Best of Luck, and don't be bashful about asking questions. There resides a veritable Brain Trust of Electronic Knowledge on this Website.

Sincerely;

LJB

[RetroHacker]

Nice work! Looks great! Congratulations on the success of your first TV project. There will be many more to come, I'm sure

With that set - does it have an aluminized picture tube? If not, it uses an ion trap. A misadjusted ion trap will result in a dim picture, even on a good tube. Basically.... the early picture tube coatings weren't too sturdy. The electron gun will, as a result of operation, emit ions. These ions are "heavier" than electrons, and if allowed to hit the phosphor coating, will wear a hole in it - resulting in a dark spot. So, to avoid this, they simply aimed the electron gun downward a bit. This way, the ions would go harmlessly into the bell of the tube, not the screen. But, then again, so do the electrons. But wait! Electrons can be redirected by a magnet. Heavier ions can't (at least not as easily). So, by using an ion trap magnet, they could bend the electrons back where they needed to be, and leave the ions to fall to the bottom. Later tubes came out with a aluminized screen, that was impervious to the ions, eliminating the need for this system entirely.

On your other Admiral - how weak did the tube test? You can get a watchable picture on even a very weak tube. Another "trick" to bring back a weak tube is to run it for a while, on just slightly higher filament voltage. Stay away from the "rejuvinate" function on the tester except for a last resort. Sometimes, a tube that's been sitting forever will come back after even just running in the set at normal voltage for a while. Something to do with the cathode coating. So, if the tube is in the red, run it at say, 7 or 8 volts (assuming a standard 6.3v filament) for a couple hours. Come back and switch it back to the normal voltage, let it run for a minute, and check the emissions, and do a life test. You might be suprised.

I have an Admiral (one of those bakelite console-ettes) with a 14" rectangular tube. When I got it, it had a brightner on it, and had a G1 to cathode short. With the tube tester, I was able to blow out the short (using remove shorts), and bring the tube back into the green by running it hot and using "clean and balance" on the tester. It's definitely watchable now. A bit dim, but watchable.

-Ian