Beginnings

When Frank Lang donated the 1948 RCA 8TS30 television to the David Sarnoff Library, director Alex Magoun asked if I would be interested in restoring it to working condition. He was familiar with my success with a 1951 Zenith television, various radios, and other tube-based equipment. During a break in my work schedule, I began.

About Vintage Electronics

Television and radio vacuum tube sets are typically not found in working condition unless at least some effort has been invested in their restoration. It is, in fact, dangerous to plug in an old set that has sat unused for decades. Many parts in such sets simply don’t have the shelf life to function reliably past their normal life span, and may cause “shorts” that will ignite fires or damage other parts that are difficult to replace.

Vacuum tubes are, contrary to common belief, among the more reliable components of vintage televisions because the internal vacuums tend to preserve them during long storage periods. The components most prone to failure include wires (especially power cords) and paper and electrolytic capacitors. Resistors can “drift” upwards in value from use, or just over time. A common strategy for a functional restoration is to replace all paper and electrolytic capacitors, and test for and replace out-of-spec resistors.

Many sets also harbor a “cause of death” waiting to be discovered. The end of the life of a set such as this is typically instigated by a failure that was either deemed too costly to repair, or the set’s performance had degraded to the point where replacement with a new set was considered wiser than fixing up the old one.

The Restoration Process

Restoring a set begins with inspection, initial repairs, and parts replacement. This is followed by a period of testing, alignment, and debugging until the set’s performance is deemed satisfactory.

The RCA 8TS30 Inspection

The power cord was found to be too damaged and degraded to have considered an attempt to “just plug it in.” The channel selector dial was crooked, which turned out to be a significant clue to a problem found deep within the set. There was ample evidence that rodents (probably mice or squirrels) had taken up residence in the cabinet. Aside from some bedding material and acorn shells, there were a few nibbled components. Considerable rust and corrosion resulted from their excretions. A few tube shields were missing, and a paper power line bypass capacitor had exploded. The outer conductive coating of the picture tube was flaking off.

The set otherwise appeared complete and undamaged.

Testing the Vacuum Tubes

All of the 30 tubes (except for the picture tube) were checked on a Philco 9200 tube tester. None were dead, but many tested weak or marginal and an audio IF tube was slow to warm up. A used picture tube was donated with this set, which was used as a replacement for the original with its decayed conductive outer layer. The high voltage rectifier was so weak (30%) that it was also replaced at this stage.

Replacing Capacitors (“Recapping”)

All of the paper capacitors were replaced with modern, reliable “orange drop” mylar parts. All of the electrolytic capacitors were removed from the circuit (though left in the chassis) and modern capacitors were substituted. A total of fifty-two new capacitors were installed.

Other Repairs Made During Recapping

A few wires from the main power supply choke coil and vertical output transformer were brittle and cracking, so insulating heat-shrink tubing was installed where bare wire was exposed. The vertical height potentiometer had a lump of solder on one of its terminals which was dangling inside its case (probably a factory defect), so it was opened, cleaned, and the lump of solder removed.

Initial Power-up

The set was powered up gradually through a Variac (variable voltage transformer). The tubes lit up. Current consumption appeared normal. A soft hiss and hum came from the loudspeaker and a weak, blurry raster appeared on the screen. Adjusting the focus control had no effect. Handling the wires to the focus coil caused the picture to flicker and die.

First Repairs

Two of the voltage divider (“bleeder”) resistors in the set’s power supply were found to be intermittent, so they were replaced with modern equivalents. A terminal on one of the tube sockets had broken off, so the socket was replaced along with the five resistors connected to it.

Second Power-up

An undersized but well focused raster appeared on the second power-up, along with the expected hiss in the audio. Changing the channel or touching the antenna terminals caused a flicker on the screen and a static sound in the speaker, but applying a signal from a VCR to the antenna terminals produced no sound or picture.

Intermittent Horizontal Output Trouble

An “intermittent” symptom is one that appears randomly and renders the set unreliable. The horizontal section has a .25 amp fuse connecting the flyback high voltage transformer to the damper tube. As soon as the set warmed up (but before any picture appeared) the fuse would sometimes blow. This proved to be a difficult symptom to diagnose, because once the fuse blew, the reason for its blowout would be obscured. After replacing all the tubes in the horizontal sweep section, the symptom vanished (but would return later).

Tuner Trouble

The presence of static in the sound and picture when the antenna terminals were touched suggested that every part of the set was working except for the tuner, and that the RF oscillator was probably dead. All of the tubes in the tuner were replaced with no improvement. The tuner contacts were cleaned, also to no apparent benefit.

Removal of the tuner for close inspection revealed that damage from rodents had been greater than originally realized. Much corrosion had resulted from the seepage of urine into the tuner from the top of the chassis. To clean it, the tuner was run twice through a dishwasher – once with detergent, and again without. Then it was left to soak overnight in distilled water.

During drying and lubrication, it was discovered that the tuner contacts were not meshing properly because the detents in the channel selector were offset by exactly half a channel. The cause turned out to be incorrect assembly (possibly at the factory) of the detent bracket. Correcting this made the contacts mesh perfectly, and allowed the crooked channel dial on the front of the set (noticed during initial inspection) to be leveled.

The tuner then functioned correctly, and the set showed picture and sound from the VCR for the first time. During the tuner debugging effort, the loudspeaker was removed from the cabinet, and the speaker’s paper cone was found to be damaged. I repaired it with rubber cement.

Horizontal Output Trouble Returns

The set apparently was working about as good as could be expected when the damper tube fuse blew out again. It was eventually found that a flyback transformer terminal was intermittently shorting to the back cover of the high voltage cage. Eliminating this short cured the symptom.

Final Installation

After adjustments to all the controls, the set gave an acceptable picture from video tape. There was some horizontal instability (typical with VHS tapes on sets of this vintage). The demonstration system was changed to use a DVD player, and the picture became stable. The set’s performance could still be improved after a complete RF and IF alignment, but the picture and sound are, as of this writing, fully satisfactory for presentation at the David Sarnoff Library.