Step by Step Restoration: GE T-106C, Let's go for it!

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Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 9:45 pm

Alright Ladies and Gentleman, as promised, here is a nice 'follow-along' for your viewing and learning pleasure on the basics of restoring an old tube radio. Today's "patient" in the radio hospital is a General Electric model T-106C. This is a miniature tube All-American Five table radio in a plastic case boasting dual speakers and "spotlight tuning" as well as anodized aluminum trim.

We'll go step-by-step. Don't be afraid to ask questions or throw your hat into the ring with suggestions or feedback. I thought this simple circa 1957 set would make a nice "intro" for those starting the hobby or starting back up where they left off many years ago.

We'll take a radio that looks like it was ready for the trash can and turn it into a presentable working piece of history that anyone would gladly have playing in their kitchen or den.

So let the fun? cheers Challenge? Smile Frustration? Embarassed Learning? cheers begin......
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The GE model T-106C is typical of baby-boom era radio cabinet and electronic design. The radio utilizes 5 miniature tubes on a printed circuit board assembly and is a superheterodyne AM broadcast receiver that is AC line powered.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 9:59 pm


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Okay, let's start at the beginning. If you bring a treasure home from a garage sale, swap meet, eBay or estate sale, the first thing to do is look for any kind of identification for the radio itself. What make? What model? What tube line-up? Finding this information will greatly increase your likelihood of finding needed data and schematics to bring things back to life (not to mention helps out your Tube Radio Forum friends trying to HELP YOU).

Luckily the model tag pasted to the back of this radio was still intact. Everything was legible from the model number to the tube location guide.

Shall we dig in???

Whoa! Not yet....Let's go over the basics. Any good technician, tradesman, mechanic, whatever needs to proper tools of the trade to do a successful job. I tried to picture the the main ones.
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A) Schematic--the electronic "map" for you to find your way through the various circuits and identify unknown or damaged components.
B) A good reliable and accurate multimeter. We'll be measuring both AC and DC voltages, both high and low.
C)An absolute must for AC/DC radios like the one that will be restored. This is an isolation transformer. This breaks the dangerous path of current between the hot leg of the wall outlet and a ground reference (the cement floor, a water pipe, a piece of test equipment, YOU or anything else that would make a complete circuit from one prong of the AC wall outlet (the "hot" side") and an electrical ground. We'll discuss more on this later.
D) A good reliable soldering iron. I like my 100 watt "gun" style unit. This allows you to heat up solder joints quickly to avoid permanent damage to the equipment you're working on.
E)Typical tools of the trade. The quarter inch nut driver will be used A LOT. This radio is no exception. You also want some miniature side cutters, needle nose pliers, various screw drivers and anything else used to disassemble without destroying.

Remember you can't do the job without proper tools!
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 10:06 pm

Another nice item to have on the bench is a Variac. This device allows you to slowly bring up the line voltage to the radio you are servicing. If there are any issues or you see (or smell!) a problem, you can quickly down-power the unit. This comes in handy for older units that have power transformers. Since this is a series-string radio (each tube is wired in series with each other like lights on a XMAS tree, there is no power transformer. The full 120 volt AC line voltage comes to light the tube heaters and get converted to DC (direct current) to run the radio circuits.



Important! A variac does NOT substitute for an isolation transformer! Some variacs have an isolation transformer built in, most do not. The variac will not prevent you from a "hot" chassis in which the AC line comes into the radio and you can risk getting shocked if you are grounded by chance as discussed above.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 10:24 pm

Okay, hopefully everyone isn't scared off on the safety issues with electrical current. As with any job with electricity, you just need to watch what you are doing and have respect for the equipment, the electrical current and yourself!

So let's look at the radio and start to dig in!
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First step is to NOT plug in the radio. In fact we can't on this one...there seems to be a small detail item missing--the cord! Was this done because there was a problem with the radio?
Was this done as someone took out their frustration on the radio?
Was this done as someone got into the radio and realized they were over their head?

The possibilities are endless. Always approach with caution. Even if the cord was there (see the circled area?), never a good idea just to "blindly" plug in electronics that are 50, 60, 70+ years old.

This radio is pretty typical. It would have had a safety interlock plug. This is a cord with a molded plug attached to the radios back. In order to remove the back, the plug gets disconnected. This way there was no power to circuits when you or anyone else was "inside". Pretty clever huh? They had to do this as back then, radio were "user serviceable", meaning Mr. John Doe radio owner could open his own radio up to replace tubes as they burned out or failed.

As they say, you can make anything fool-proof, but you can't make anything idiot-proof!

So our 1/4" nut driver comes into play to remove the bottom attaching hex-head screws. Once those are removed, the back slides down out of the top retainers and then simply out. Had the cord still been attached, you'd have to slowly pull until the prongs disconnected from the interlock cord.


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Well whaddaya know? Guess what was rattling around inside...the missing cord....Here's the inside scoop. I purchased this radio online back in the 1990s. I honestly can't remember if it was completely missing it's cord, or came with a cord that wasn't connected. So, I placed this cord inside for future use. Since I am unsure of the history of the radio, we will treat it like any other--with caution.........

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These style of cords are also referred to as "cheater cords" as you can "cheat" and connect them without having them attached to anything restrictive like the back of the radio. This allows for you to power up the radio, albeit dangerously if you don't know what you are doing?

So shall we plug it in? We have an isolation transformer, right? WRONG. Again, we are going to take this step by step. We'll do a total tear-down and properly investigate things. More importantly we will replace the electrolytic filter capacitor to begin with before we even attempt to power it up. More on this troublesome filter capacitor later.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 10:39 pm

Here's another reason for the complete tear-down and rebuild---yuck! When something sits around for decades you know what happens when the average user has no way to clean dust and dirt out of it......


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This is pretty typical. This radio actually isn't too bad, I've seen much much worse! Shocked

This is why I always "bag and tag" radios I bring home until I get a chance to work on them. You never know what nasties are lurking inside and you don't want them in your house! Lucky for us, there were not bugs or rodents in this one, just a lot of soot, dirt, grime and dust!

Also, nothing looks out of the ordinary. No black tape splices, damage or "creative modifications". It's always nice to work on an unmolested radio as opposed to having to un-do someone's genius handy-work Evil or Very Mad

Okay, so first thing's first...completely disassembly means removing things that will only hold up progress...Pull the knobs right?


The volume knob pulls straight off the ribbed control shaft, but wait, the tuning knobs doesn't seem to want to budge.....

STOP! Like many other radios, this radio uses what is referred to as a "captive" knob. The tuning knob can NOT be removed by simply pulling on it....More on this later. Since this is the case, we'll start back on the inside....


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I've taken the time to show what needs to be done. You must identify all the hex-head screws to be removed to pull the circuit board out of the radio housing. Don't forget to desolder the leads that link the chassis to the speaker! There are (5) 1/4" hex head screws holding the circuit board in place. There is a 3/16" hex-head holding the neon pilot/dial light in place. Don't forget the screw holding the interlock prongs in place--bottom right of picture!

I use desolder braid to unsolder connections. I only worry about the black and green wires for now, they need to be removed so we can continue on.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Fri Feb 01, 2013 11:08 pm

Okay, time for a quick visual. Everything that currently "can" be removed has been removed.....Speaker leads from chassis desoldered, circuit board screws removed. Pilot light assembly screw removed. Volume knob removed. No other apparent trim or components in the way.

Here's a helpful hint*******Many times the schematic or service literature will indicate what you have to do to disassemble a radio. These are always great especially if you aren't familiar with what "captive knobs" are and other pitfalls!

Well that stupid tuning knob is the only thing keeping our circuit board from seeing the light of day! First thing to do is turn the tuning knob so the tuning capacitor's (in the middle of the board) blades are fully meshed. You don't want them sticking up as you'll be grabbing the assembly by the strongest part--the tuning capacitor and don't want to risk damaging those fragile "fins".

Now it's time to play the least favorite game of the radio servicer---tug-of-war! Razz

It seems like an impossible catch-22 as you can't pull the circuit board assembly out as the tuning knob's shaft is still on the capacitor's shaft. You can't pull the tuning knob off as it is being held captive.....

SO...you must pull a little in each direction with one hand grasping the tuning knob and the other hand grasping the circuit board by the strongest part--the tuning capacitor's frame. You'll actually pull more on the circuit board as it will have much more travel. Remember in this game, it's possible for everyone to lose! No Cracked circuit board and broken plastic tuning know if your not careful!

And...finally!



As you can see, there is a little clip assembly that has "vampire teeth" that bite into the plastic of the tuning knob's shaft. This is what keeps the darn thing captive. The board assembly then pulls straight off.

So why all the trouble? Manufacturers did this to prevent shock when a bare shaft was left from small inquiring minds that had pull a knob off, also was a way to keep important knobs from getting lost!

So now the printed circuit board assembly has been "liberated" from the cabinet. Home stretch now on disassembly! cheers

Time to pull out the dual speakers. As you can see, there was no need to desolder all of the speaker wires, only the two that fed the speaker circuit. You paid attention to where the green wire and the black wire went? Right? Always important to make notes or take pictures!

To keep things simple, we'll pull the speakers as a set.


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Same basic idea here. Hex-head screws holding the speakers on. GE used rubber spacers to hold the speakers tight and it also provided some shock absorbing qualities. Sometimes the rubber "barrels" don't want to slide off the plastic posts. Simply take needle nosed pliers and give them a good twist/pull and they'll usually pop right off.

A walk in the park in comparison to the captive knob fiasco....


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Speaking of knob fiasco, we need to get that dangling tuning knob off! No need to scratch-up the wonderfully bright anodized trim behind it as it swings freely.

I've had good luck using picks and tiny needle-nosed pliers to make the vampire lose his bite Razz

Carefully bend up where the tabs "dig in".


Don't trash it though, we'll want to re-use it!

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At last!!!! A completely stripped cabinet.



Stay tuned.....

Bath time is next!!! Razz
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Resistance is Futile on Fri Feb 01, 2013 11:37 pm

One of the things that I would bring up would be to look for the schematic when you first get home. Before you proceed with a tear down of the radio, you need to make sure that the schematic is available. And I would suggest that before going any further then the radio should be inspected to see if there's any catastrophic damage. (That way you have an idea whether the radio is worth repairing before going further.) If the radio has a schematic, you are one step ahead, in case you run into serious trouble with repairs.

You do show a very good idea in taking photographs of each step of the process. And as you said it will help when you start with the radio back together, because Murphy's law always raises its ugly head in the process of repairs.
I applaud you and you're presenting your repairs. I'm sure the newer members will gather some good information from your demonstration, thank you.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Guest on Sat Feb 02, 2013 10:13 am

Very good so far! I would suggest taking care with the removed speakers as the permanent magnet types can attract parts or other imetal objects that can damage the cones when you lay them down.

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Guest on Sat Feb 02, 2013 10:43 am

Dr. Radio you are doing a great job. I hope more of us can follow your example! Very Happy

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Sat Feb 02, 2013 9:10 pm

Excellent points. Thanks for the feedback guys.

Cliff, yes, schematic availability can be a major issue. In fact, it almost derailed this project. There actually isn't a schematic for it, specifically, that is. I wanted to feature a radio that had an exact schematic for ease of explanation-- I have some official GE literature that lists models using pictures for a few model years. It shows this radio, but lists models ending in "A" and "B". No "C". The other versions use a 12AU6 tube (which this radio doesn't) and no mention at all of a pilot lamp. I'm going to use a more generalized schematic that covers the basic printed circuit board in this radio and many, many others GE produced from the late '50s thru the early '60s. Because of a little investigative work today, I made a surprising discovery on this radio in regards to its production--more on this later.

Also good point on the speakers. Been there, done that, when it comes to the "oops" when a cone gets punctured or ripped.

Shall we continue on?
Smile

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Sat Feb 02, 2013 9:46 pm

Time to start cleaning things up...I hate letting dirty pieces and parts just linger around the bench. Normally I would say focus on the electronics first, but since there is relatively low-risk in this radio (even if there was a catastrophic fault in the electronics), the availability of parts are almost literally a click away thanks to eBay, electronic want-ads, etc. Besides, I have many parts sets as well I could "rob" from if need be.

Now, this would be a totally different story if this was a high-end console radio with a bad power transformer or other major component that was faulty and difficult to find a replacement. You'd definitely want to focus your energies on the chassis before you worry about the cabinetry. No need to spend time and money getting something "beautiful", only to have sit in the corner not working with a paper-weight for a chassis due to major issues or parts made of "un-obtanium". Embarassed

We won't worry about the detailing and polishing yet, let's just get it cleaned-up for now. This radio's case will be a breeze to clean now that we have stripped out all of the electronics and there is no model/schematic label pasted to the cabinet that we have to worry about ruining with water and cleaning solutions.

In another area of this forum I posted my favorite cleaning supplies. I'll be using just two to start with--regular warm tap water and some Simple Green cleaner I've diluted in a spray bottle. I start by spraying some of the cleaner at the bottom where all of the dirt and grime has settled. Rinse and repeat Razz

Don't forget the radio's "ceiling". The top of the cabinet is usually just as filthy with "soot". This "soot" is basically the result of dust getting heated and burned from the heat of the tubes. It rises with the heat and collects on the top of the cabinet. A little scrubbing with nothing more then my rubber gloves got the vast majority of it off.


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It's always amazing to see the results of a little water, a little cleaner, a little TLC and sometimes a LOT of elbow grease. Very Happy
Although the pictures are a bit misleading (there is still a lot of grime and residue in the louvers that make up the speaker mounting areas, it is still a long way from where we started from!

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The only word of caution is be careful if the radio has any special trim that could easily be marred, rusted, damaged or destroyed by the cleaning process. This radio uses "bright work" that is basically nothing more then thin anodized aluminum trim that is painted to give an eye-catching two-tone effect and glued into place. I was careful not to use any harsh cleaners that could damage this on the front of the radio.
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Again, as we get closer to completion, we'll worry about the detailing (getting the grime out of all the louvers, nooks and crannies).

Okay, as a teaser, here's a before and after shot of the clean-up on the tuning knob. Not bad eh? cheers


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Up next will be the careful cleaning of the printed circuit board assembly--so we can investigate what we have and identify the trouble areas....

Stay tuned....... Smile


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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by jerryhawthorne on Mon Feb 04, 2013 6:57 pm

Nice thread and thanks for posting. Even those of us that have done a lot of radios always have something to learn. Great effort and very helpful.

Jerry

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Resistance is Futile on Tue Feb 05, 2013 5:57 am

Yes I noticed after you did the cleaning, your fingers even took on a different patina. LOL
Seriously though when I do that step on cleaning, I always use a toothbrush on the grillwork using 409 as it is a little stronger in my opinion. But simple green is a good cleaner.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Wildcat445 on Tue Feb 05, 2013 1:40 pm

I cover any labels with clear shipping tape, then stick the plastic cabinet into the dishwasher. I turn off the drying features and use the "energy saver" setting that only allows warm, not hot, water into the dishwasher. They come out sparkling. No scrubbing. No dirt left in the corners. Clean inside and outside. I have several of those cheap GE radios and I kinda like them. There are practically no parts in them, they clean up easily, the wife thinks they are cute, and they perform surprisingly well for what they are. They usually have a couplet somewhere, but they don't normally cause problems. The filter caps can be tricky to change until you get the hang of how to do them.

Regards

WC

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Bill Cahill on Fri Feb 15, 2013 6:19 am

Anything new on the radio??
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Ken g on Fri Feb 15, 2013 9:47 pm

Bill i think its a ''used radio '' so nothing new Wink

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Bill Cahill on Fri Feb 15, 2013 9:52 pm

Laughing

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by mikehall on Sun Feb 17, 2013 12:06 am

Very enjoyable thread!

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Mon Feb 18, 2013 9:35 pm

Okay then.. Surprised

Back to this little GE after getting sidetracked on some more pressing projects.

Well, it's bath time once again, but this time, we're not going to use water, as we are cleaning the electronics! It's much easier to work on something that isn't filthy with decades of grime Embarassed


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It's best to work in a logical order. Although it appears no one has done any "customization" of this radio Mad , it does appear it has been worked on in the past more then once. The evidence of this is the fact that some of the tubes are different brands. When a radio left the factory, it had that particular manufacturer's labeled tubes in it, so obviously when I found a Westinghouse and RCA brand tube, it tells me this radio isn't all factory original!

The first step is to use our factory tube chart and compare that with the tubes we find in the respective sockets. Don't assume that someone hadn't goofed in the past.

Remember we were fortunate that this model still had it's factory tube locations legible on the original model tag....
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Now it's just a matter of pulling one tube at a time, removing grime so we can verify it is the correct tube for that socket. Luckily, the tubes in place matched the tube location label and the schematic--always what you want! 3 out of the 5 tubes present appear to be the factory originals. If this radio contained all original tubes, I would have carefully cleaned the tubes to retain the original "artwork" on the tubes just for historical purposes. Miniature glass tubes were printed with paints that easily rubbed away. This was done on purpose to make it harder for people to sell used tubes as "new". Evil or Very Mad



Now that the tubes' identities have been confirmed, they get carefully put to the side--remember the rarer the tube, the more likely it will find a cement floor to shatter on! Sad

Taking advantage of some mild weather I decided to take printed circuit board assembly outside and carefully start brushing away the dust bunnies. I used a soft bristle toothbrush. That took care of most of it. For the more tricky nooks and crannies I brought it inside where I could use cotton swabs and pipe cleaners to clean out the areas that are tightly packed with components. I used some rubbing alcohol for dipping the swabs into to clean some of the dirtiest areas. The idea is to take your time and be use care. As pictured below, one fragile area is the trimmer adjustment screws on the tuning capacitor. They have mica sheets under the screws that can easily get torn. As a general rule, if you don't use harsh chemicals, compressed air or hard bristle brushes you'll be okay. Don't use anything like steel wool that could leave hundreds of little "short circuits" waiting to happen.




Well, how's that?! Now we can see what we are working on! Razz

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Mon Feb 18, 2013 10:07 pm

Time to focus on the restoration of the printed circuit board assembly. We'll be replacing the bad components and doing some "preventative maintenance" work as well.

I couldn't label every component, but labeled the the main items we'll be looking at throughout this resto.



The radio's "guts" are pretty typical of the baby-boom era. It uses the "AA5" (All-American 5) tube layout. 12BE6 (oscillator), 12BA6 (IF amp) 12AV6 (detector), 50C5 (power output), and 35W4 (rectifier) and a minimum of parts to get the job done.

The first thing we'll replace is the electrolytic filter capacitor. Electrolytic capacitors are one of the most failure prone items you'll run across in vintage radio restoration. It's the filter capacitor's job to "filter" or "smooth out" the pulsating DC that leaves the rectifier tube. Since the capacitor has a chemical paste inside, time and heat eventually cause this paste to break down. Most capacitors of this nature go "open" leaving no filtering, so you hear 'HUUUUUMMMMMMMMM' if the radio is powered-up in this condition. Sometimes the capacitor can short internally and have the potential to damage the radio's circuitry. Due to the nature of the beast, we won't even power this up until we replace this capacitor in the very least.

The replacement is fairly straight-forward, you just have to obey some safety rules. The filter capacitor is the easiest component to identify, it's literally one of the largest parts--ours is the large cardboard tube. The first thing to pay attention to is the orientation of the capacitor's legs. You'll notice they are lettered......


For the newbies, it's never a bad idea to either make a witness mark on the capacitor's body and the circuit board, so if there is any question later on what pin went where, you can recreate the factory placement by lining up your marks. You could also take a fine marker and literally write the letter on the board where the pin passes through.

Why's this so important? Filter capacitors have polarity. They typically have a "common" negative and a number of (+) pins. Reverse connections and you could literally be in for an explosion!

We can see "B" and "C", but "A" is obscured by it's mounting on the board. We'll get a better look when we pull it out of the board.
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Mon Feb 18, 2013 10:51 pm

Time for some more desoldering....After flipping over the circuit board to the trace side, you have to identify which pins you need to desolder. The cardboard tube has 3 "legs" that pass through the board and are slightly bent to hold the capacitor in place. Using the soldering gun and some solder wick, the solder is removed. You need to avoid excessively heating (keeping the solder gun or iron on the connections too long) the area or you risk "lifting" a trace or connection pad, not to mention the potential for damaging the board.



The key here is to try to remove enough solder to provide a hole for the pin to pull though. You may need to rock the pin with a pair of needle nosed pliers. All the connections have to be free to remove the capacitor. More experienced restorers can "rock" the hole capacitor after heating up each connection a little to break it free. Don't pry or force as you could end up with broken parts you didn't need to replace or splashes of solder everywhere Rolling Eyes (never a bad idea to wear eye protection as well when desoldering).
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And that's how it's done.... Smile

Okay, now to see what we have....(3) pins and the letters designate the capacitor's values. Like most, this is a multisection unit--meaning it actually has (2) capacitors in the same package, they just share a housing and a common negative (meaning the negative leg of each capacitor is tied together to "A").

In order to get the proper replacements, we need to know the value of the capacitors and the voltage ratings. This original has a 30 microfarad --shown as mfd, notated here as "uF" section and a 50 uF section. Each section is rated for 150 volts.


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You'll find many old electronic values have changed to new standards. For example, 50 uF is no longer a standard issue value, 47 is. Same way with 30...it's now 33. These values are very close, so we don't have to worry about the minor differences in capacity.

Voltage rating--this is VERY important. Just like the polarity, if you don't pay attention to this, you are literally setting yourself up for disaster. You can always go with a higher voltage rating, but NEVER go with a lower one. 150 volts is no longer a "standard", but 160 is. And since we're higher in rating, we're okay.

As you can see, modern technology is much smaller! Razz



As indicated, you must keep track of the proper (-) and (+) connections on the new units as well. The manufacturer of these units use a dashed stripe to indicate the negative legs on the same side. We'll have to tie these negative legs together in the original negative connection on the board (where the "A" pin" went through). We'll also have to ensure we match up the proper value of capacitor with the respective connection. In other words, make sure we don't install the 47 uF capacitor in the circuit where the 33 uF unit belongs.


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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Mon Feb 18, 2013 11:01 pm

Up next....more on filter capacitor replacement....and.....some detective work to find out something interesting about the actual year this radio was manufactured. Hint: This radio wasn't built during the Eisenhower administration!
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Sat Feb 23, 2013 8:33 pm

Okay, Let's continue on with the electrolytic filter capacitor replacements....

Not a bad time to verify the connections (if you failed to mark the original orientation of the factory capacitor OR if the radio had been previously worked on--many times the filter caps have already been changed at least once in the radio's service life due to their failure rate). Time to get out the schematic (your electronic road map) and follow the traces on the board with the electronic notations on the schematic to get your bearings.



That's what is nice about Photofacts, you can literally compare your unit to the one in print side-by-side.


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We'll look at one of the connections that lead to the (+) of one of the filter capacitors. Shown as "6", this is a reference for the power supply connection found throughout the radio. We found it literally by matching up the traces with those pictured. Now, to see it in "electronic notation", or simplified in a circuit view.

Here's the same point "6" which provides the filtered B+ 90 volt output to the various stages of the radio. This is used to see the relationship of what value capacitor ties to what point. Our 33uF capacitor's (+) lead needs to connect to this point.



*Helpful hint*, many times a schematic won't be exact due to running manufacturing changes, or encompass multiple models, this schematic is based on a clock radio, so if you were paying close attention you would have notice what looks like a discrepancy between our radio and the schematic..........Our radio uses a dual section filter capacitor, 30uF and 50uF. The schematic shows a 75uF capacitor instead of the 50.....that's not a problem, our uses the 50uF as it is not a clock radio and doesn't need the extra filtering. A good tech needs to look at the big picture. Cool

Quiz time: Do you know why a clock-radio would have a filter capacitor(s) with greater capacity (resulting in more filtering of the pulsating DC out of the rectifier tube)?? This is quite typical. Post a reply if you know and we'll see who gets it first and with the correct answer Very Happy
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Sat Feb 23, 2013 9:59 pm

Now that we know what value capacitor needs to go "where" and we are aware of the importance of making sure the polarity is correct for each capacitor so we don't have an explosion Shocked , it's time to actually mount the new components on the board. As pictured earlier, my new capacitors are MUCH smaller in size, and the leads are reflected in this smaller size. Since the "footprint" is different, this presents a new challenge.

For the newbies out there, I recommend trying to get ahold of replacement electrolytics that are different then the ones I have pictured. They are getting harder to find, but axial style electrolytics will be easier to work with, especially with printed circuit boards....

Here's why:



With axial style, you have more versatility, easier to "stretch" over to the needed connection point. Here's a picture of a different radio's circuit board. You'll notice the axial capacitors get the job done quickly. The two negative leads are tied together at the common point and the positive connection leads go to each respective circuit point. This arrangement is a bit crude, but get the job done. It also adds some strength to the mounting so the capacitors aren't just "swinging in the breeze" as they are tied down at each end.


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The ones I have in stock are radial lead where both "legs" exit the capacitor at the same end. Since this is what I have to work with, I'm going to modify my printed circuit board by drilling small holes (carefully) so the capacitors can sit correctly on the board. I consider it poor workmanship to use radial capacitors and just "bend out" the legs at extreme angles to the factory connection points. This usually leads to capacitors "swinging in the breeze" with poor mechanical connection strength and the risk of short circuits.

Here's what will basically have to be done to modify this circuit board so it becomes more "modern" to accept the radial lead capacitors.....



I start by carefully making note of the area of to work with. I don't want to accidentally drill into the wrong traces on the other side of the board. I want my new "paths" to be short in distance and provide reliable connections. I carefully drill the holes for the leads of the 33uF capacitor to pass through. Then I drill holes for the 47uF capacitor's leads to pass through. Where I need to make a connection to the appropriate trace, I scrape away the green conformal coating off of the trace so I have good clean copper area to solder to. I then "tin" the area by applying a small amount of solder over the raw copper area of the trace. This becomes my new connection "pad".


With the new "factory" set-up ready, I carefully slide the legs of the 33uF capacitor through the board. Again I make sure I have the proper polarity, the (-) connection of the capacitor is getting to the (-) aka common side of the circuit board traces



Now, after the capacitor is inserted, I bend the leads over to the new "pads" I made so they can be securely soldered in place. The excess leads sticking up are then carefully cut close to the solder points so there is no risk of short circuits.


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I now do the same thing with the 47uF capacitor. I ensure the leads are connected properly to the board.


It may seem like a tight fit, but again, I had to provide mounting in relationship to the proper electrical traces, not solely based on the space available on the top side of the board.

Here's the trace side of the board again. The (+) side of the 47uF has to "jump" over another trace, and to ensure there is no risk of a short circuit either now, or in the future, I slip over a piece of teflon wire insulation over the lead and push it down so it becomes a barrier between the capacitor's lead and the trace directly below it. All connections are soldered carefully and extra lead lengths are cut off.

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Re: Step by Step Restoration: GE T-106C, Let's go for it!

Post by Dr. Radio on Sat Feb 23, 2013 10:31 pm

We're getting ever-so-closer to powering this chassis up for a test, but there are a few more things we'll go over first....

For now, here's a little break for your education and your entertainment....Most people think electronics work would have little to do with detective work, but they often go together hand-in-hand! Rolling Eyes

Remember a few posts ago when I mentioned I had learned something interesting about this radio's date of manufacture? This brings up something I want to share. Many times people will ask or post "how do I know how old my radio is?", or "what year was this set actually manufactured?". Many times it's as simple as doing a little investigative work.....

There's a couple things to remember first in regards to those common questions. For starters just because a radio is a 1938 model, it doesn't mean it was actually made in 1938. Just like automobiles, radio manufacturers had model years. They may have started building a "new for 1938" radio in July of 1937. Automobiles are the best example of this, you might own a 1993 model year car, but I could have been actually built anytime between August of 1992 and May of 1993 for example. Another thing to remember is sometimes manufacturers "recycled" a design. Brought back a cabinet or chassis from a previous model and "updated" it to sell as the latest and greatest--this helped keep buyers coming back, but kept costs down.

I've been working on plastic post-war GE table radios for many years. I can tell you without a doubt, GE was "notorious for recycling" back in the 1950s and 1960s---reintroducing radios that used the same cases or same basic chassis that were introduced many model years ago. Most would receive minor "facelifts", different trim, clock mechanisms, color combos etc. I should of remembered this when I started this project.

As I stated earlier, I have some official GE service literature that provides actual pictures of the radios contained in the booklet as well as a date of that set. It listed T-106A and T-106B (no "C" model which is what we have) and showed 1957 as the date of this radio.

Well as I dug into this set, some things just did not seem right for a 1957 era radio. I've worked on a lot of GE plastic radios and this one definitely seemed "off".

First off, there are NO paper/wax capacitors in this set. There are ceramic disk capacitors used where typically there would have been a paper or even a plastic molded capacitor. Sure they had ceramic disks in 1957, but for this simple radio, there surely would have been at least one paper or molded plastic capacitor on the board.....

Secondly, because of the "C" suffix in the model number, this means something was changed or added. Sometimes this can be minor (such as a volume control part number change), or major, like a different cabinet color. Obviously this one used a different tube layout, the radio we are working on doesn't use a 12AU6 tube....but I was still thinking this doesn't fit the bill as a radio only having minor changes like a tube substitution.

Third, this was the biggest clue of all for someone familiar with GE consumer radios....


Remember this???

I removed it by unsoldering its leads. I didn't want it getting in the way while I worked on the chassis.... Unlike most radios that use a miniature incandescent lamp apart of the rectifier circuit, this neon pilot lamp doesn't do anything for the radio's circuitry. It's wired in series with a resistor to limit current, but it gets it's power directly from the AC wall current coming in to the radio. It's used as a power on indicator and also provides a lit "dot" on the station tuned in.

SO? Well this bugged me as a GE enthusiast---it was not until the early 1960s that GE started using miniature neon lamps in consumer radios so there was no way this radio could have been built in the 1950s!

So when was it built? That's what I'm getting to.....the best way to find out WHEN a radio was manufactured is to use the clues given by.............. bounce
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Re: Step by Step Restoration: GE T-106C, Let's go for it!

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