General Electric Model 810 Television (1949)

              

              

This General Electric Model 810 television is a classic 10-inch set from 1949. The styling is dramatic, with a brass control panel and outsized fabric grille.

Finding a GE 810

I spotted this TV in a local craigslist ad in Spring, 2018. The TV was listed for $75, but the listing disappeared before I got around to contacting the seller. Next week, the ad reappeared, and the price was reduced to an irresistible $25! Here's the 810 when I got it the next day:

  

The cabinet is in decent condition and it includes the often-absent back cover. We'll get a peek at the internals soon.

Description

GE was a major radio company by the late 1940s, but their entry to the TV market was tentative, with only four models in 1947 and one more in 1948. That changed in 1949, when GE released more than twenty new sets, including this one.

In this catalog pic from the TV History website, the 810 tabletop appears in the upper right:

For a tabletop TV of this vintage, the GE 810 is a middleweight. It's larger than 7-inch sets like my Admiral 19A12 (left), but more compact than my 10-inch RCA 630TS (right), which can live on a tabletop or a stand:

  

The model 810 television uses 22 tubes:

Tube Type Function
V1 6AU6 RF Amplifier
V2 12AT7 Converter/Oscillator
V3 6AU6 1st Video IF Amplifier
V4 6AU6 2nd Video IF Amplifier
V5 6AU6 3rd Video IF Amplifier
V6 6AL5 Video Detector/Clipper Rectifier
V7 12AU7 Video Amplifier/Limiter
V8 10FP4 Picture Tube
V9 6SN7GT Vertical Sweep Generator
V10 6V6GT Vertical Sweep Output
V11 6SN7GT Phase Inverter/Clipper
V12 6SN7GT Horizontal AFC/Sweep Gen.
V13 6BG6G Horizontal Sweep Output
V14 1B3GT High Voltage Rectifier
V15 5V4G Horizontal Damping
V16 5U4G Low Voltage Rectifier
V17 6AU6 Audio IF Amplifier
V18 6SH7 Audio IF Limiter
V19 6AQ7GT Audio Discriminator/Amplifier
V20 6K6GT/G Audio Output
V21 5Y3GT Low Voltage Rectifier
V22 6AU6 Audio IF Amplifier

Here is the Riders service manual for this set. To download it, right-click on the icon and choose Save Target As:

(This manual, along with many others, is hosted at the Early Television Foundation website.)

First Look

Before investing too much time in this set, I need to test the picture tube; if it's a dud, replacing it might cost $100 or more. This TV uses a 10FP4 tube, an aluminized jug that produces a bright picture if in good shape.

I slid the socket off the end of the CRT and connected my Sencore CR70 tester:

As often happens with long-unused picture tubes, this one looked nearly dead at first. But the emission needle crept upward when I let the tester run for a while, and it ended up in very respectable territory. If I can get the rest of the TV working, I expect it to make an image with good brightness and contrast.

  

That's an encouraging sign. Let's pull the chassis and get started! Here are photos of the unrestored chassis from above and below:

  

Yes, you can stand this chassis sideways on the workbench (power transformer down), but it's rather tippy with that heavy CRT in place. During parts of this project where the big tube isn't important, I'll pull it and substitute my smaller 5AXP4 test CRT.

The next step is to test and clean the TV's 21 small tubes. As described in my first restoration steps article, it's convenient to clean the chassis as you go along.

Of those 21 tubes, only one was bad. Our chassis looks better after this initial cleanup.

Using DeOxit, I cleaned all the TV's potentiometers and the contacts in the tuner.

First Power

Like every 1940s TV, this one is full of old paper and electrolytic capacitors that should be replaced for safe and reliable service. (For more information about capacitor replacement, see my recapping article.) My workshop stash didn't have all the needed caps, so I compiled a list and made an online order.

Meanwhile, I'm curious whether I can coax any signs of life from the unrestored set. I don't often do this, but I decided to try powering it up without even replacing the electrolytics in the power supply. Being an optimist, I turned the channel selector to channel 10, the one I use to broadcast throughout the house with my home TV transmitter.

I didn't just turn the set on, however. It's prudent to power an unrestored TV using a variac, gradually increasing the line voltage, and keeping a close eye on the TV's current consumption. If the draw is excessive (suggesting a short circuit somewhere), you can quickly power down before damaging a power transformer or other component.

For this first trial, I left the big 10-inch CRT in the chassis. Things sounded good at first. I gradually turned up the line voltage and heard nothing but a few faint crackles, until the audio kicked in, at around 90 volts AC. It sounded good enough to understand dialogue in the program on channel 10.

When the voltage reached about 100 volts AC, I could faintly hear the sweep circuits starting to run. But the CRT remained completely dark, and a peek at the CRT's base revealed the reason: the picture tube's filament was not glowing, possibly due to a loose filament pin in the base.

Bummer! This picture tube looked great before, but now it's conking out. Perhaps all is not lost, though. Loose filament pins can often be cured.

I pulled the big CRT and set it aside for future investigation, installing the little 5AXP4 tube in its place. Here's the setup, with my metered variac on the left and a test speaker connected to the audio output. I tuned the GE to channel 10, the same channel playing on another TV in the background.

I increased the voltage slowly, giving the 71-year old electrolytic capacitors a chance to re-form if they're able. When I reached around 100 volts, I was rewarded with some light on the screen. Hooray!

Okay—it's not the greatest picture in the world. But remember, this TV is completely unrestored, except for replacing one dead tube. And we can tell a lot from this brief trial, even though the screen looks like blobs.

The screen lights up and the audio is respectable. That tells us the power supply (including high-voltage supply) is working, and every section of the TV can pass a signal and process it, from front to back. The contrast and brightness controls have an effect when I move them, as does the fine-tuning control. The image is badly out of focus, but I'm using a substitute picture tube and haven't yet adjusted the focus coil on its neck.

The horizontal hold control works normally, but the vertical sweep has big problems. I can't lock the image vertically and, as seen in the previous photo, there are two identical blobs stacked vertically, a sign that the vertical oscillator is running at roughly half the correct speed. Vertical problems are very common in old TVs, and I hope this will clear up naturally when I recap the vertical sweep circuits.

All in all, this brief initial test is encouraging. Unless some hidden problem appears, I expect this restoration to be straightforward.

Rescuing the Picture Tube

Let's try re-flowing the solder in the pins of the big 10FP4 picture tube. If that repair fails, I'll need to find a replacement CRT, which might be costly.

The next photo shows the basic idea. Using a soldering gun or iron, you heat each of the tube's pins until the solder flows inside, adding a small amount if needed to make sure the pin is full.

Don't heat the pin more than needed to re-flow the solder; excessive heat can crack the glass in the tube neck. When you're done, make sure that the end of each pin is neatly rounded, as it was before; use fine sandpaper if needed, to remove any excess solder.

I re-tested the CRT, and it looked great! Remember this simple trick, if you have a picture tube whose filament doesn't glow on the tester. Five minutes with a soldering gun may save you the cost of a new picture tube.

Replacing Paper Capacitors

Now, I'll start replacing this TV's 38 paper and electrolytic capacitors. In this photo, the two brown Chiclet-shaped caps are new, and much smaller than the old paper one that I just replaced.

The value 473 printed on the new cap denotes the value .047 mfd, functionally equivalent to the .05 mfd value printed on the old one. Its voltage rating of 630 volts slightly exceeds the original 600-volt rating. My recapping article has more details about choosing and installing replacement caps.

Here's a cap near the volume control that would be easy to overlook. Follow the green arrow to spot the tan paper cap hidden behind the little terminal strip.

In the next photo, I have replaced all three of the paper caps seen in the last shot, bringing the hidden one into the open to simplify future service.

The audio output circuitry is cramped, with one small electrolytic (C93) and two paper caps (C77, C79) in tight quarters. These photos show the area before and after replacing those three components:

  

Fast forward a few hours, and we've made progress. Here's the TV after I replaced nearly all the paper caps (but no electrolytics):

The picture looks better, but the vertical problem remains. Here, we see three stacked images. The vertical oscillator is running at roughly one-third the normal speed: about 20 cycles per second, rather than 60.

Fixing the Rolling Vertical

Vertical circuits are often easier to debug than horizontal ones. The following schematic shows the heart of the vertical section, a conventional "multivibrator:"

Recapping had eliminated some obvious suspects from this circuit: paper capacitors C30, C31, C41, and C34. I also tested the vertical output transformer (T15) with an ohmmeter and found nothing amiss. I checked all the resistors and didn't find anything wildly out of tolerance, although I did replace a few that were somewhat over the line.

After replacing those resistors, the vertical almost worked, meaning that I could sometimes get it to lock by turning the vertical hold control all the way clockwise and adjusting other controls very, very carefully. That's not how the TV should work, though.

Then I noticed the asterisk next to resistor R110 in the previous schematic. Way down in the lower right corner of the schematic is this little starred footnote:

Looking back at the schematic, we see that resistor R110 is a 24K resistor in series with R28, an 82K resistor lying between the vertical oscillator's grid and the vertical hold control. When I shorted out R110 (effectively removing it from the circuit), the vertical hold improved at once. I could easily lock the vertical and the locking point was near the center of the control's range, as it should be.

At last, we have a stable picture! The video's a bit smeary, but it's still early days.

Replacing Electrolytic Capacitors

Although the TV played safely (in short trials) with its original electrolytic capacitors, I know from experience that 70-year old electros aren't trustworthy for the long haul. Even if they seem OK, they can fail at any moment, in the worst case frying the TV's costly power transformer. Out they go!

This set has ten electrolytic capacitors, eight of which are contained in a pair of cans on the rear of the chassis. This photo shows most of the replacements; eight will go into the tall cans and two more will go under the chassis.

After removing the cans, I'll install new caps on the original bases and then put the hollowed-out cans back in place, another procedure described in my recapping article.

  

The new capacitor leads run through holes drilled in the bases, and then they are soldered underneath to the original terminals. Here are the replacements installed on their bases, ready for the cans to be glued back on.

Check Out These Flexible Resistors

While replacing an electrolytic (C102) under the chassis, I encountered this unusual component:

This is a flexible resistor (R105) with a very low, and very precise, value of 1.0 ohms. It is labeled R102 in this unusual circuit, which supplies filament voltage to a single tube:

In the words of the service manual:

To prevent hum modulation by the local oscillator when operating on the high
frequency channels, the filament supply to (converter/oscillator tube) V2A is
rectified by the selenium rectifier SR1 and filtered by C102:

Hum is a bad thing, but I haven't seen a circuit like this in other TVs. I wonder if GE added it to cure a hum problem unique to this design?

Flexible resistors are thin coils of resistive wire in flexible "stockings," usually with low resistance values. You can read more about them in my Stewart Warner 1865 article.

A second flexible resistor with even lower resistance (0.65 ohms) is used in one of this TV's low-voltage power supplies. Here is R97:

Both resistors checked out fine, so I left them alone. If you need to replace one, use a standard modern resistor with the specified resistance and wattage.

Crashing and Burning

At this stage, the TV displayed a coherent picture. These photos show it using my small 5AXP4 test CRT and the full size 10FP4 tube:

  

Some issues remained. Most obviously, the TV suffered from an intermittent snap-crackle-pop that made hash on the screen and noise in the audio.

Moving the tuner affected this interference, so I cleaned all the tuner contacts a second time with DeOxit. This reduced the crashing but didn't eliminate it.

I began to make systematic voltage and resistance checks, working my way along the signal path. It didn't take long to find more problems. On pins 6 and 7 of V4, the 6AU6 2nd video IF amp, I found (and replaced) two resistors. They were so badly burned that they fell into pieces when I removed them:

I should have noticed those toasted guys in my initial inspection. In any case, they're gone now. But the crashing was still audible when the TV warmed up.

On a hunch, I turned off the lights and powered up the TV in darkness. During the initial power surge, I saw flickering on the socket of V7, the 6AU6 second audio IF amp.

I cleaned that socket with isopropyl alcohol, then probed around the socket pins with a dental pick, looking for burned spots. Between pins 6 and 7, I dug out black, charred phenolic, the result of arcing between the pins:

Arcing between pins 6 and 7 of a 6AU6 tube creates a short circuit between the tube's grid and cathode—not what the designers intended!

I dug out as much black stuff as I could reach in that cramped area, and briefly tried the TV again. Sometimes, if the arcing damage isn't too great, you can remove the conductive carbonized material and leave an air gap large enough to prevent arcing. Then you can fill the gap with non-conductive epoxy and salvage the socket.

When I tried the TV again, the arcing in that spot was even brighter, a sign that the socket still has a conductive carbon track that I can't reach. Time to find a new socket!

Replacing a Burned Socket

This phenolic body of this odd socket is wider than normal for a 7-pin tube, indicating that the chassis was originally punched for a standard 8-pin tube like the octal 6SH7 right next door:

I couldn't find a replacement socket from the usual suppliers, but I eventually got one from a fellow collector. It fits!

  

The old socket was fastened with rivets, which I removed by grinding down their heads. (Trying to drill out a rivet simply spins it in place as soon as the bit digs in.)

I replaced all five components attached to the socket:

     

Why did this socket fail in the first place? There's no way to be sure. Liquid such as mouse urine in the socket might cause a short between pins, but the chassis has no obvious staining or rust in that area. Or, the socket might have degraded all on its own; these cheap wafer-type tube sockets are near the bottom of the quality scale. (At the top end, you'll find expensive ceramic sockets like those in my National TV-7W.)

Whatever the origin, once arcing starts, it can burn a carbon track along and then into the phenolic, as happened with my old socket. But my brand-new replacement should last indefinitely.

Losing and Regaining Audio

With the new socket and components in place, I tried the TV again. The audio quality was good, indicating that I hadn't made wiring errors and the audio alignment was still within the ballpark. I still heard crackling, however.

I resumed the systematic voltage testing that was interrupted when I noticed arcing. This required playing the TV, of course. At some point in this process, the audio weakened and then went silent.

What's going on? I tested all the audio tubes, to rule out a sudden tube failure (they were fine). Touching a powered soldering gun to the middle terminal of the volume produced a loud buzz, showing that the audio output section (with 6K6 tube) worked. That left the two 6AU6 IF amps and the 6AQ7 discriminator.

I re-checked the voltages on the audio tubes and didn't find dramatic changes from the last testing round. However, I was reminded that the plate voltages were high on both IF tubes. On V22 (1st IF), the voltage should be 100V and I measured 140V. On V17 (2nd IF), it should be 105V and I measured 195V.

That led to more resistor testing around the audio tubes. I eventually found an intermittent solder joint on a pair of joined terminals on a terminal strip near the audio IF tubes, where several components connect to a B+ line. Nudging that crowded junction changed the resistance reading, indicating a cold or broken joint. In this photo, the junction is largely hidden by a big 22K resistor.

The green arrow points to an example of sloppy work at the factory. The foil ground strap appears to physically touch the adjacent terminal, a terminal that is not supposed to be grounded! I guess that terminal wasn't actually grounded—if so, the entire B+ line would short out—but this slapdash handiwork doesn't inspire confidence.

Rather than simply re-flow the old solder on this messy junction, I decided to remove everything and connect new parts cleanly. This involved replacing the same parts I had replaced on the other audio IF socket, with one additional capacitor.

This photo shows the transplants installed on V17 (bottom) and V22 (top).

I tried the TV again, and the audio came back. A tweak to the discriminator transformer made it sound even better. But I could still hear crackling in the audio, sometimes accompanied by fleeting white hash in the picture.

Tuner Cleaning Redux

Interference in both video and audio suggests a problem farther back in the signal chain, such as the tuner. Experimenting with the tuner convinced me that it wasn't making good contacts. Interference appeared when I switched off-channel and back again, or simply rocked the tuner shaft.

I have seen those symptoms in dirty wafer tuners before, so I decided to clean the tuner for a third time. I used liquid DeOxit D100L and cotton swabs, rolling the buds tightly to avoid leaving tiny fibers behind.

It's not easy to reach parts inside this tuner, especially near the front. I held the wetted swab on each moving contact and then turned the tuner back and forth through all its channels a few times.

After cleaning each contact, I went back and cleaned each area with isopropyl alcohol, to avoid leaving excess cleaner on the phenolic wafers. I let the assembly dry overnight under a low heat lamp.

When I tried the TV the next evening, the tuner changed channels cleanly and the TV played a long time with no video hash or audio static. The snap-crackle-pop has been vanquished, at least for now.

One Step Forward and Two Steps Back?

The next time I tried the TV, the picture tube suddenly went dark. A moment later, the choke in this photo started to sizzle and spew molten wax:

This choke (L20) helps to filter the 360-volt B+ output from the TV's power supply; it is connected between two electrolytic capacitors (C58, C62):

Fearing that the sizzled choke was ruined, I got a replacement from an eBay vendor and installed it:

When I tried the set again, I slowly increased the line voltage using my variac, watching its ammeter closely in case a short circuit was still present. At roughly 90 volts, when the low-voltage rectifiers began to conduct, the ammeter needle swung sharply to the right and pegged at the top of its scale, indicating a short in the B+ supply. I immediately powered down and started to hunt for a cause.

Fixing a Short Circuit in the B+ Line

When faced with a short circuit, you must distinguish between cause and effect. I first assumed that the sizzling filter choke (L20) simply failed on its own; but replacing the choke didn't cure the excessive current drain. The choke's overheating was a symptom, not the cause, which must be a short circuit somewhere farther down the B+ line.

This TV has two separate low-voltage power supplies: one provides 360 volts and the second provides 290 volts. This schematic marks the origin of the 360-volt supply at the downstream side of choke L20:

The 360-volt line leading off to the right connects to several circuits: the 1st video amplifier; vertical multivibrator; vertical output; horizontal AFC; horizontal size and linearity; flyback secondary coil and damper tube; and horizontal deflection coil.

This full schematic highlights the 360-volt B+ line in red:

That's a lot of territory to cover, in search of a short circuit. I began at the 360-volt origin: the junction of choke L20 and capacitor C62. If electrolytic filter capacitor C62 developed a short, that would ground the 360-volt line and put L20 under great stress.

Like most of the 810's electrolytics, C62 is contained in a can, and I had replaced C62 earlier, along with the other electros. By now, the TV had played happily on the bench for hours and I had previously measured 373 volts at the 360-volt origin point, well within a normal tolerance (±20V). New caps don't fail often, but anything is possible, so I disconnected C62 and it checked OK. The short must lie farther down the B+ line.

The B+ circuit branches into multiple nodes, so finding the short meant disconnecting those nodes at various points and testing many components. Eventually, aided by a tip from the Antique Radios TV forum, I found the short in an unexpected place: inside the yoke that holds the vertical and horizontal deflection coils.

Throughout this testing, I had consistently found a low resistance—roughly 40 ohms—between the B+ line and ground, wherever I checked. But when I disconnected the vertical deflection coil's ground connection, the resistance jumped up from about 40 ohms to nearly 80 ohms. Aha!

Further testing revealed a very low resistance between the vertical and horizontal deflection coils, so I removed the yoke for further inspection. The yoke's barrel is gripped between movable jaws; you can slide it out after freeing the tensioner springs:

  

The horizontal and vertical deflection coils lie in close physical proximity, both wrapping around the neck of the picture tube. But they should be electrically isolated from each other. The horizontal coil connects to B+ voltage via the damper tube and flyback transformer, whereas one end of the vertical coil is grounded. If a short should develop between the two coils, that will ground the B+ line. This schematic shows, in somewhat roundabout fashion, where the vertical coil connects to ground:

To check for an inter-coil short, I connected my ohmmeter between one terminal of the horizontal coil and one terminal of the vertical. A normal yoke should have infinite resistance—no connection—between the two coils. My yoke measured only a few ohms resistance between the coils. Bingo!

Somewhere inside, there's an electrical path where there should be none, likely due to crumbling old insulation. This yoke was not designed to be disassembled and repaired. It is listed as a single part in the service manual and the whole assembly is glued together firmly, discouraging investigation.

I bought a replacement yoke from the same guy who earlier sold me a replacement choke. In this photo, my defective yoke is on the left:

I double-checked the new yoke to confirm it had no internal shorts, and then installed it. The short circuit was repaired and my picture reappeared!

  

Replacing the yoke took only a few minutes, but I had spent hours in search of the short: taking measurements, tracing connections, and checking components. In repairing a few dozen vintage TVs, I have never run across a bad yoke, but there's a first time for everything. This is one lesson I won't forget!

Adding Retrace Blanking

Like many early TVs, the original version of the GE 810 displays slanting "vertical retrace" lines if you increase the Brightness and Contrast controls beyond a certain point. This photo from another project shows such lines:

Late in the 810's production, GE added a simple circuit to suppress these lines, but my early 810 didn't include it. This service note explains how to add the retrace blanking circuit:

Here, I have laid out the needed parts: two resistors and two capacitors:

Two of the parts can be mounted on an unused terminal near the Brightness and Contrast controls:

  

Thanks to retrace blanking, now I can adjust the contrast and brightness to achieve a very nice picture—with no slanting lines!

I found this service note in Volume 2 of Rider's TV Manufacturer's Receiver Troubles and Cures. The Receiver Troubles book (in six volumes) is a good resource to check whenever you restore a vintage TV.

Adjusting Screen Geometry

Now I can adjust the screen geometry, using my Philips PM 5518 TV pattern generator:

Here, the pattern generator is creating a basic crosshatch pattern, overlaid with a circle pattern. I have adjusted the TV's geometry controls—vertical size and linearity, horizontal size and linearity, and centering—so that everything looks symmetrical and properly centered.

In the GE 810, the size and linearity controls are electronic adjusters that you screw in or out while viewing the screen. You center the displayed image on the picture tube by rotating two circular magnets located on the picture tube's neck.

After the TV is reinstalled in the cabinet, I'll tweak the geometry controls one last time, so that the edges of the TV image fit the cabinet's screen opening precisely.

Cabinet Restoration

With the electronics under control, I turned to the cabinet and its brass trim. The wood finish is presentable, but the brass is badly worn and corroded in spots.

Disassembling the cabinet and trim means removing several nuts and wood screws from inside:

Removing the brass bezel frees the safety glass:

In the next photo, I have removed the speaker and the little round GE emblem; a green arrow points to the spot where the emblem's nut was fastened. I put the speaker mounting nuts back on their screws, to avoid losing them.

The big brass faceplate is fastened to the grille with nuts on the inside, and its edges are clamped in place by the wooden frame in front. In addition to removing the nuts, you need to remove several wood screws to release the frame.

In the next photo, I have removed (and reversed) the frame and I'm ready to pull the faceplate, which fits into the recessed frame edge. A few thin brads, like the one by my finger, help to position the frame precisely against the cabinet front. Don't remove the brads; they'll help you align the frame when reinstalling it.

The previous photo shows that a prior owner repainted the edge of the cabinet's screen opening—normally, a pale blue-green—in a garish dark blue color. What was he thinking?? Let's repaint that edge later.

Restoring the Brass Trim

I'll need to strip the big brass faceplate, which is weathered and corroded in the usual wear areas. Where the lacquer coating remains, it is yellowed and sloppy. Look at the hairs and dirt captured in the old lacquer near my thumb:

In the next photo, I have stripped off the old lacquer with oven cleaner and begun to polish the faceplate with Brasso. (You can polish brass with just about any sort of metal polish.) This looks ugly, but don't worry—the piece will look good after I finish polishing and then re-lacquer it.

The faceplate is solid brass, so you can polish it aggressively without danger of scrubbing through thin plating.

Stripping removed some of the lettering, which I'll restore it with a red Lacquer-Stik:

I washed the entire piece with isopropyl alcohol to remove any stripping residue. After the alcohol dried, I rubbed the crayon-like lacquer material into the incised lettering and then buffed away the excess with paper toweling.

  

After removing the excess color, I re-washed the surrounding areas with isopropyl alcohol and Q-tips. When you're prepping brass for lacquer, the metal must be clean, clean, clean!

I used the same methods to strip and polish the small round GE emblem and the rectangular screen bezel. Then I sprayed all the trim pieces with a few coats of lacquer:

If you need to restore incised lettering and you can live with a limited color palette (red, black, or white), lacquer sticks are easier and faster than laboriously filling each letter with a tiny paintbrush. The stick material is stable and you can lacquer over it immediately.

Cabinet Refinishing

The cabinet wood is in nice shape; it only needs a light refresher. After cleaning the wood with paint thinner, I applied a thin coat of mahogany stain and immediately rubbed off the excess. That concealed the little scuffs without darkening the overall color. I let the stain dry overnight, buffed the wood again, and sprayed on a few coats of clear lacquer to protect the finish and add some depth.

Let's reassemble the cabinet with all the brass parts and safety glass:

Everything looks good, except for that garish blue border around the screen opening. I had hoped the blue wouldn't be very noticeable when reassembled behind the brass bezel, but it sticks out like a sore (and incorrect!) thumb.

I repainted the border in the pale blue-green hue seen in photos of other 810s.

The cosmetic restoration is complete.

Injecting Video and Audio

The TV worked well now, but I wondered if it would play even better if I injected video and audio directly, rather than bringing in a signal through the antenna.

These photos show the picture quality at this stage. The TV is receiving a program over the air from my in-home TV transmitter:

  

That picture's not bad, but let's find out whether it can be improved.

On many vintage TVs, signal injection is straightforward. The idea is to disconnect the TV's native video and audio signals right where they are passed to the video and audio amplifiers. At those two spots, we substitute video and audio signals taken from a DVD player or similar source of composite video. The topic of injection is covered in more detail in my article A-V Adapter for Vintage TVs

On the GE 810, you can inject audio at the "upstream" terminal of the volume control (R86), and inject video at the grid (pin 2) of the 12AU7 video amplifier tube. These schematics show the injection points:

  

The next photo shows the injection points under the 810's chassis. I have temporarily disconnected the signal lines and clipped in lines carrying audio and video from a DVD player.

The experiment worked, so I decided to install an A/V adapter. All that I need is a little project box; two shielded cables; three female RCA jacks (one for video, two for stereo sound); and two 10K resistors (to combine the stereo channels into a mono signal).

I could mount the input jacks by drilling holes in the back of the TV chassis, but that's too invasive for my taste. This little A/V box can be hung non-destructively on the TV's rear cover:

The new signal cables are threaded through existing holes in the chassis and soldered in place underneath. If a future owner wants to reverse this modification, it will take only a few minutes to disconnect these lines and restore the original connections.

These photos show how I installed the new audio line on the TV's volume control:

     

Wiring the video line was a similar process.

The results are gratifying:

Now, I have clear sound and an excellent picture!

To Inject or Not

Video injection in the GE 810 has a minor side effect—disabling the Contrast control—that sounds bad but has little practical impact.

In this TV, the so-called Contrast control should properly be named a Manual Gain Control, since it adjusts the amount of gain (amplification) in the three video IF circuits that precede the video amp in the signal chain. The effect is to increase or decrease the overall signal strength. (Long time readers of this website may recall a similar design in the RCA 630TS television, which uses the name Picture Control for its manual gain control.)

In a world with analog over-the-air TV broadcasting, some kind of gain control is useful to compensate for differences in signal strength between powerful local stations and weak distant stations.

Say that you're station-hopping and you adjust the picture to look good for a strong station. If you then switch to a faint, faraway station, the picture may look washed-out or even snowy.

Some older TVs like the GE 810 or RCA 630TS have a manual gain control for making this adjustment by hand: if you increase the gain for a weak station, it may look as good as a strong one. More advanced TVs like my Admiral 24C15 have an AGC (automatic gain control) circuit to compensate for signal strength automatically.

Nowadays, any kind of gain control is irrelevant, because we feed our vintage TVs from devices like DVD players that output a strong, constant signal. (This is true even if you are listening to digital over-the-air programs with a converter box. The signal level from the box is constant, no matter if the digital signal received by the box is weak or strong.)

That is why losing the functionality of the Contrast control (aka manual gain control) doesn't matter.

Of course, just because it's possible to inject signals, doesn't mean that you must do it. In this GE 810, the picture quality from an injected source is noticeably better than from a conventional source, so the decision to inject was easy.

I reached the opposite conclusion when I restored my DuMont RA-102 television. Rare, valuable, and historically interesting, the DuMont is in a different class than the comparatively cheap and common GE. Although I got injection to work on the RA-102, I decided to err in favor of originality and leave the set unmodified.

Shakedown Cruise

Before declaring any restoration complete, you should give your device a nice, long bench test, to make sure that it is stable. I played the set for several hours on my workbench, while I finished this article and did some other website updates:

The 810 completed its shakedown cruise with flying colors. On to the next project!

Final Thoughts

This TV turned out to be more work than I expected. Remember that burned tube socket? And how about the defective yoke that fried a filter choke? The end result was satisfying, though. Here are two photos of the restored GE 810:

  

Now, I just need to find a place to put it. Space is tight in our crowded house, but this little set is too attractive to push onto a back shelf.

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