Pilot Model TV-37 "Candid" Television (1948)

The Pilot TV-37 "Candid" is an unusual vintage television. With a tiny 3-inch picture tube, the TV-37 is barely watchable by modern standards, but its compact size and unusual design make it a favorite of collectors.

Pilot introduced the TV-37 in 1948, at the then-amazingly low price of $99. Most TVs of the time sold for hundreds of dollars, the cost of a decent automobile. Pilot made this set for only a few years, but sold a lot of them during that time. Many TV-37s still survive.

I have been told that Pilot marketed this set especially to college students, although I think it would have been a lucky student of the time to get one as a gift. The owner's daughter told me that she recalled neighbors crowding into their living room to get a look at this new-fangled invention.

Description

I was lucky to purchase this one from the daughter of the original owner. It had been well cared for, and the owner even did some restoration work on during the 1960s, leaving detailed notes.

The TV-37 is housed in a streamlined cabinet with a wooden base and an upper case made of pressboard. The entire TV is only 14 inches wide, 13 inches deep, and 9.5 inches high. Most of the upper case is perforated for ventilation.

My Pilot also came with a magnifying lens, which is placed in front of the picture tube to enlarge the image.

These magnifiers were an optional accessory, as was a pressboard carrying case with built-in antenna. Magnifiers are harder to find the TVs themselves, since not everyone bought them and some were lost over the years.

The magnifiers typically hooked onto the horizontal grill bars, but mine stands on little metal legs that slip under the cabinet. The owner's notes include a pencil mechanical drawing with dimensions for the magnifier and legs, so I surmise that he built the legs himself and painted them to match the painted trim on the magnifier. It's actually an improvement over the original scheme, since the heavy magnifier tended to warp or break the thin grill bars.

The front controls are simple: power/volume, brightness, tuning, and contrast. The tuner control includes a high/low switch, which lets you select two tuning ranges. The low range is channels 2-6 and the high range is channels 7-13.

The next photo shows the TV-37 with its hat off.

Notice the round tuning dial below the picture tube. When the case is on, it is viewed through a triangular opening. The tuning ranges are shown in two semicircles. The small speaker is mounted on a frame next to the picture tube.

Restoration

The cabinet required no cosmetic restoration, apart from touching up a couple of tiny paint nicks on the base edge. Like all TVs of this vintage, the set will need electronic restoration to be made safe and reliable.

The electronic design is quite similar to other electrostatic-deflection TVs of that era, such as my 7-inchers, the National TV-7W or Motorola VT-73.

This television uses 21 tubes, including a 3-inch electrostatic-deflection picture tube.

Unlike most TV tuners, the Pilot's is continuously variable. Instead of clicking from one station to the next, it turns smoothly, like most radio tuners. This was a cost-saving measure. The Pilot tuner contains far fewer parts than other TV tuners.

Another cost-saving (and weight-saving) design tactic was to eliminate the expensive and heavy power transformer. This is a transformerless "series string" TV, in which the tube filaments are connected in series. As in many radios, the voltages of the tubes add up to the voltage of the AC power supply (around 120 volts). Given the number of tubes, it actually uses two parallel tube strings, a design repeated in some other TVs such as my Philco Predicta.

The next photo shows the components under the chassis when I purchased the set.

The previous owner had already done a fair amount of restoration work, replacing a number of capacitors and a few resistors.

I'd guess the work was done in the 1960s, judging by the type of components used and the fact that the owner retired in 1965. He replaced most of the original, unreliable paper capacitors (see Replacing Capacitors) with modern, epoxy-dipped components. These should still be reliable, so I'll leave them in place for now.

There are still about a dozen paper capacitors hiding in the chassis, including the critical high-voltage capacitors, and a few electrolytics. Those will be replaced by me.

Before making any replacements, I cleaned and lubricated the tuner and all of the control potentiometers (volume, brightness, etc.). The tuner and two potentiometers were completely stuck on their shafts, but I freed them up with a penetrating solvent followed by electronic cleaner and lubricant.

The 3KP4 Picture Tube

As far as I know, the Pilot was the only consumer television to use a 3-inch picture tube. Even primitive kit TVs of the 1940s used larger tubes. The Pilot's 3KP4 is also notorious for burning out, because it is subjected to a great power surge when you turn the set on. As a result, 3KP4s are scarce and costly.

To cure the surge problem, I will install a Triad F-13X filament transformer (6.3 volts, .6 amps) between the power line and the picture tube. Since the CRT normally presents some resistance in the filament string, I will install a 12 ohm, 10 watt power resistor at that place in the string.

Some Pilot owners substitute the more common 3KP1 picture tube if their original 3KP4 is burned out, or simply for testing purposes during restoration. The 3KP1 is electronically interchangable, but it was designed for use in 1940s oscilloscopes with green screens.

That substition has two major drawbacks. A green phospor tube is considerably darker than the white phospor 3KP4 and it has slower response to changing images. Things moving on the screen can appear smeared or blurry. If a character runs across the screen, he may leave trails behind like Casper the Ghost!

Since a 3KP4 cannot be tested on any tube tester, I couldn't tell at this stage whether mine was good. I tested the filament with an ohmmeter, and found that it has continuity, so at least I knew that it was not a total dud. It still could be so worn out that it's too dark to view, however. Only restoring the rest of the electronics will tell me that.

Capacitors, Capacitors

After receiving some new parts in the mail, I began replacing capacitors. The new ones are usually quite smaller than the old ones, making it easier to fit them into tight spaces.

Notice the white capacitor rated for 6000 volts. It's important to replace the video coupling capacitors with a type similar to this, rather than a ceramic disc, which will usually be unstable in this application. You can order the correct type from a supplier such as Just Radios or Allied.

I replaced all of the electrolytic capacitors, including a couple that looked like 1960s replacements. On some TV-37s, capacitor C2 was mounted underneath the chassis. On mine, it was mounted in a can atop the chassis. There is plenty of room underneath, so I mounted all of the replacements down there and left the old cans in place to preserve authentic appearance.

Note that two of the power-supply electrolytics, C2 and C3, are installed with their positive leads connected to the chassis ground. This is different than what you'll see in most radios and TVs. Don't install those two backwards—your TV won't work!

Don't forget the capacitor inside the high voltage cage.

Pay attention to the little copper collar on the midsection of the 1B3GT tube. It is important for correct high voltage output. Before removing the tube for testing, I marked its position with a Sharpie and took care to slide it back into the right place. You can read about the purpose of this connection in my Motorola VT-71 article.

First Power-Up

With new electrolytics and high-voltage caps, it was time to try firing up this TV. I connected it to a variac and slowly brought up the voltage, looking and listening for any signs of trouble.

All of the tube filaments began to glow, but there was no sign of a raster (picture) on the CRT. I could hear a putt-putt sound from the speaker, which became faster as I increased the voltage, but no real audio.

Time for some voltage checks! I quickly determined that the B+ voltage was much lower than specified in the schematic.

I re-tested the two rectifier tubes (25Z6GT and 35W4) and re-cleaned their pins and sockets, just in case of a bad connection. The B+ voltage was still too low. Acting on a tip from a fellow TV-37 owner, I connected a modern silicon diode across the 25Z6 tube, between pins 3/5 and 4/8, with the positive band of the diode pointing to the positive lead of electrolytic C1A.

That brought the B+ voltage up to a normal level. On the next power-up, I was delighted to hear excellent audio from the TV on its upper channel range, indicating that the TV's tuner and audio sections were basically functional. Not so good on the lower channel range, but we could defer that investigation until later.

High Voltage Testing

The absence of a raster suggested that we still had problems in the high-voltage power supply—often the trickiest section to restore in any vintage TV.

The data sheet for the 3KP4 picture tube indicates that you need a minimum of 1000 volts and a maximum of 2500 volts.

You can't test high voltage with an ordinary multimeter. I have two probes suitable for this. The one on the bottom of the photo is my favorite, a Pomona 2900A. It operates all on its own. The probe on the top is an RCA WG-284, which can be used with my old RCA Senior Volt-Ohmyst tester.

Testing indicated only about 800 volts, where you would expect to measure at least 1 kilovolt. That explains the lack of a picture!

Resistors, Resistors

In the high voltage section of an electrostatic-deflection TV, you will typically find several resistors with values over 1 megohm, and the Pilot is no exception. It has resistors of 1, 1.2, 2.2, 2.7, 3.9, and 4.7 megohms in the video circuits.

Old carbon composition resistors often drift upward to higher values, and the higher the initial value, the worse the drift. Starting with highest values first, I found that mine had drifted badly, sometimes as much as twice their original value.

After replacing several of the worst resistors, I was a little disappointed to find that the high-voltage level hadn't improved noticeably.

A Light Bulb Goes Off

Then I remembered that a few of the 1960s replacement capacitors were not "maroon drops." Three of them were white, apparently cased in ceramic, and the fourth was a large yellow Mallory "Plascap."

I hadn't run across either type before, but I dimly remembered something about ceramic tubular caps being paper capacitors in disguise—and potentially as troublesome. I sent a brief query to a vintage TV forum and got a consensus that both types should be replaced.

Here are photos of the 1960s culprits, shown with their modern replacements. I didn't have a .25 cap in stock, so I wired two caps in parallel to make up a usable value.

First Picture!

After replacing those caps, the next power-up gave the first pictures I had seen from this television!

Now, there are still many things wrong with this picture, but it's always exciting to see an old baby like this come back to life. Best news of all, the image indicated that my rare CRT was not a total dud.

The picture was not very bright, visible only in a darkened room. The vertical and horizontal sizes were both too large, causing the image to extend over all sides of the round CRT, rather than presenting a rectangular image that would fit inside the mask of the TV's cabinet.

The overly big vertical size accentuated the horizontal scan lines, and the vertical and horizontal centering were also a bit off, but these are all things that you can adjust by twiddling controls.

In the first photo, you can also see a few bright slanty horizontal stripes near the top. This is typical of 1940s televisions and can usually be eliminated by adjustment of the brightness and contrast controls.

Sixty years later, many of us have forgotten that early TVs required frequent adjustments, even when switching from one station to another, to get the best picture and sound. Not to mention the need to move the antenna.

These photos were taken using a rudimentary 1950s rabbit ear antenna. Given that we live in an area where all broadcast signals are pretty weak, this was a very encouraging sign.

Final Thoughts

I need to do a little more work on this set before I'll consider the project finished. Stay tuned . . .