Scott Model 800-B AM/FM/SW Radio (1947)

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The Scott Radio Laboratories Model 800-B is a better-quality postwar tube radio. With a dual chrome-plated chassis, 24 tubes, and a host of features, this set was aimed at well-heeled buyers.

The 800-B receives FM and shortwave in addition to the standard broadcast (AM) band. Motorized pushbutton tuning and high-quality audio make this set convenient, as well as enjoyable to use. Special-order 800Bs equipped with a remote control allowed the listener turn the radio on and off, adjust the volume, and tune in preset stations with the remote.

The first photo gives you a general idea what the Scott 800-B looks like in a cabinet. (The photo actually shows an earlier model that lacked shortwave coverage and had no motorized tuner.) Several factory cabinets were available, featuring mahogany or walnut veneer and brass hardware.

The console shown above is not my radio. It belongs to an acquaintance whose collection I photographed several years ago (see A Visit to Radio Heaven). The radio which I own is a bare chassis, without cabinet or phonograph. The next photo shows my 800-B, complete with vintage dust, immediately after I bought it.

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The larger chassis, shown on the right, contains the tuner, all AM receiver circuitry, and the FM RF section. The smaller chassis on the left contains all power supply components, the audio amplifier, and the rest of the FM circuitry.

The 800-B is effectively two separate receivers—AM and FM—with a common power supply, audio amplifier, and controls. The radio has separate magic tuning eyes for AM and FM, one on each side of the dial.

The radio's front panel was designed by Walter Dorwin Teague, a famous designer of the time who also created the stunning Sparton Bluebird and Nocturne mirrored radios. The large, fluted, chromium knob below the dial is the main tuner. Scott ads of the day described it as a "handsome hunk of chromium!" The other knobs are dark plastic with dark red triangle indicators. All of the knobs are mounted on a faceplate of greyish brushed aluminum.

Two rows of pushbuttons are found on either side of the dial. In addition to switching power off and on, the buttons allow you to switch between AM and FM and to choose preset stations.

Early 800-Bs have nine preset buttons for AM and three buttons for FM. Later sets allow you to program any button for either AM or FM. My radio is clearly a native of Washington state. Its preset buttons still carry labels for local stations such as KIRO 710 AM.

The 800-B uses 24 tubes, including two magic tuning eyes. Here is the tube lineup:

Tube Type Function
V1 6SK7 AM RF amplifier
V2 6J5 AM oscillator
V3 6SA7 AM mixer
V4 6SK7 AM IF amplifier
V5 6SK7 AM IF amplifier
V6 6H6 AM 2nd detector
V7 6E5 AM tuning eye
V8 6AG5 FM RF amplifier
V9 6C4 FM oscillator
V10 6AG5 FM mixer
V11 6AC7 FM IF amplifier
V12 6AC7 FM IF amplifier
V13 6SJ7 FM limiter
V14 6SJ7 FM limiter
V15 6H6 FM discriminator
V16 6E5 FM tuning eye
V17 6J5 1st AF amplifier
V17 6J5 1st AF amplifier
V18 6J5 2nd AF amplifier
V19 6SL7 Phase inverter
V20 6L6 Audio output
V21 6L6 Audio output
V22 5Y3 Rectifier
V23 5Y3 Rectifier
V24 0D3/VR150 Voltage regulator

With two stages of AF amplication and a push-pull final audio stage, the 800-B has plenty of oomph. Separate bass and treble tone controls let you adjust the tone to your liking.

The 800-B has three additional controls more commonly found on high-performance communications receivers. The three-level selectivity (bandwidth) switch lets you choose broad, medium, or narrow selectivity. This is useful for shortwave listening when stations are crowded close together. Narrowing the selectivity lets you zero in on the desired station and exclude interfering signals from its neighbors. Under uncrowded conditions, you can choose broader selectivity for better audio.

The continuously variable sensitivity control lets you lower the receiver's sensitivity to avoid being overpowered by very strong signals.

If you click past the stop at the top of the sensitivity range, you switch on the radio's noise filter circuit. The filter is useful for removing "spiky" type noise, such as interference from the ignition of a poorly shielded auto engine. You can use the filter at any time, although, again, it is most useful for shortwave listening.

The sensitivity and selectivity controls operate only in AM mode, where they are useful for "DX-ing" weak and distant stations. AVC (automatic volume control) is available in AM mode, but not in FM. As a result, you may find yourself turning the volume down for very strong FM stations.

The power supply is conventional, but it includes an extra voltage regulator tube to maintain stability if your line voltage fluctuates. This is another feature found on expensive communications receivers such as my Hallicrafters SX-88.

The power supply includes two transformers, one to power the receiver circuitry and the other to power the drive motors and relays. The 800-B has three relays, which are used to switch the power on and off, switch between FM and AM modes, and mute the audio when changing stations via the motorized tuner. Two motors are used, one for the automatic tuner and one to change the volume via the remote control.

Much of this radio's mechanical complexity derives from the remote control. Duplicating controls on the remote dictated the use of relays and motors rather than simple manual switches and controls.

I have never seen a remote in person. A few years after I first published this article, a visitor emailed me a couple of photos, noting that someone had paid $650 for this scarce item.

  

The 800-B is an electromechanical marvel, but the many moving parts and mechanical contacts can make it a repairman's nightmare. If you service an 800-B, pay close attention to cleaning and lubricating all contacts, motors, and relays. I recommend doing this before attempting to power up the radio, in fact. If a relay or motor is frozen in the wrong position, applying power could cause expensive damage. The motors are practically impossible to replace unless you cannibalize another 800-B.

Initial Cleanup

My 800-B was extremely dirty at the time of purchase. The next photo shows the tuner chassis from above. As you can see, I had just begun wiping the dirt from the beautifully chromed chassis.

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The following photo gives a closer view of the cleanup process. Look at all the dirt on that paper towel!

In the next photo, most of the surface dirt has been cleaned up. A large chrome cover has been removed, exposing the radio's large tuning capacitors. In this view, the radio's knobs and tuning dial are to the right. The large circular apparatus at the left of the photo is the auto-tuning backplate. We'll look at that interesting gizmo in more detail later in this article.

Chromium-plating was a luxury feature on Scotts and similar high-end radios. Unfortunately, the chrome used on Scott chassis was not the best quality, tending to rust and peel over the years. The chassis on my 800-B is pretty decent, but it does show some light rust pitting here and there. The tops of a few of the transformer cans show some peeling, too.

It's possible to have chassis parts re-chromed, but that would involve stripping the chassis and then completely rebuilding it—a gargantuan task for a set of this complexity. Since the chrome on mine is not that bad, I'll just live with the blemishes for now. If I eventually build a cabinet for it, nobody will see the chrome, anyway.

The mahogany wood on the front panel is in excellent shape, needing no restoration.

Electronic Restoration

When I bought this radio, it was missing the original speaker. It also had serious power-supply problems, as I later discovered.

Substituting Speakers

Before powering up the radio, I had to lash together a replacement for the missing speaker. The original 800-B speaker is a 15-inch coaxial unit, meaning that it has two speakers mounted on the same frame. One speaker is the bass and the other is a tweeter. The speaker assembly includes a crossover network to route high frequencies to the tweeter and lower ones to the bass driver.

The speakers are electrodynamic and their field coils serve double duty as chokes in the power supply filter circuit. In plain English, this meant that I couldn't power up the radio at all until I duplicated the missing circuitry.

Since I didn't have two electrodynamic speakers lying around the workshop, I used two permanent-magnet speakers instead. To subsitute for the field coils, I wired in two resistors which gave the same resistance value as the original chokes. These, along with the crossover components, were soldered to the multi-pin Jones type plug that connects the speaker to the audio/power chassis. Fortunately, whoever removed the chassis from the cabinet had the sense to unsolder that plug and stick it in the chassis rather than leaving it behind on the speaker cable.

The resulting setup was not pretty, but it did work. With speakers wired up and the rest of the circuitry in place, I was ready to power up the radio for the first time. Before doing so, I had cleaned and lubricated all the radio's contacts and controls, replaced bad dial lamps, tested all of the tubes, and replaced a few weak ones.

Firing It Up (Literally!)

As found, this radio had a short circuit in the first filter capacitor of the main power supply. After replacing that capacitor, I slowly brought up the power using an autotransformer. The radio played on all bands, but after a few moments I heard a sizzling sound from one of the two rectifier sockets. Looking more closely, it appeared that the socket was starting to bubble and melt!

I quickly powered down and did some testing. Perhaps the socket was carbonized inside, providing paths for high voltage to leak to the chassis. This damage might have occurred when the radio continued running after the filter capacitor failed. In any case, both rectifier sockets had a strange, mottled appearance. I decided to replace both of them.

Replacing Rectifier Sockets

The following photo shows the rectifier sockets. One of them, at the bottom, has already been unwired. In the upper left of the photo, you can see the base of the defective filter capacitor. It has a large hexagonal mounting screw and has also been disconnected.

Looking more closely at the defective filter capacitor, I saw that it must have suffered catastrophic failure. The aluminum case was heavily oxidized, as if from overheating, and its sides had even dimpled inward somewhat. While leaving the capacitor disconnected, I polished up the case and left it on the chassis to preserve the radio's original appearance.

The next photo shows the chassis after I had removed both rectifier sockets. The replacement sockets are also shown.

In the previous photo, the large transformer to the right of the socket holes is not the main power transformer. It is an auxiliary power transformer supplying DC voltage for the radio's drive motors and relays.

With new rectifier sockets in place, the sizzling problem had disappeared, but another one now appeared. When I powered the set up again, smoke and a crackling sound came from the power transformer.

A little testing showed that the transformer had an internal short. Ouch! The power transformer is often the most expensive component in a radio, and this one would be difficult to replace. It supplies three separate filament voltages in addition to the radio's high-voltage B+ supply. The next photo shows the transformer out of the chassis, with one of the casings removed. A sorry sight, indeed!

Replacing the Power Transformer

If you ever "smoke" a transformer, you won't forget the distinctive, sharp odor of burning varnish. Luckily, I obtained a replacement transformer from fellow collector Walt Heskes. The new transformer's specifications were almost the same as the original, except that the B+ supply was somewhat lower.

Not knowing how well it would work, I first connected the transformer with temporary leads. To my delight, the radio performed beautifully despite somewhat lower plate voltage on the audio output tubes. I decided to mount it permanently, using a couple of spacers and handmade brackets to adapt it to the chassis without making any new holes. The next photo shows the new transformer in place on the power chassis.

A Scott purist would see at a glance that the transformer has been replaced, but I doubt that most other people would notice. Another option would have been to send the original transformer to a specialist to be hand-rewound, but the cost of that would have exceeded what I paid for the entire radio! I have saved the old transformer just in case I or a future owner decide to invest in rewinding later on.

The original transformer supplied 390 volts of B+ current, while the replacement supplied only 310 volts. This translated to a deficit of about 90 volts at the plates of the audio output tubes. The schematic calls for 340 volts at those points, but I measured only about 250 volts using the new transformer.

To test whether the lower voltage really mattered, I cranked up the line voltage on my variac as high as it would go. This increased the plate voltage to about 300 volts. The radio didn't seem to perform any differently at the higher voltage. In both cases, it had excellent sensitivity, tone, and volume. Concluding that the lower voltage made no difference, I decided not to make any further modifications to increase the B+ level.

With a new transformer in place, my project was almost complete. The next photo shows the underside of the tuner chassis.

Tasks Left Undone

Visible at several spots underneath this chassis are rectangular, metal-cased "bathtub" style capacitors. At the time of this restoration, I was told that these are oil-filled capacitors, expensive and very reliable units that are more often seen in military-grade equipment. Since the radio was operating well, I decided not to replace them. As I learned when restoring my second 800-B (see below), this advice was not correct.

I also decided not to disassemble and clean the motorized tuning assembly on the rear of the tuner chassis. The service manual explains how to do this, but after lubrication my motorized tuner worked just fine, so I stopped there. The next photo shows the large rectangular assembly on the back of the tuner which allows you to adjust the tuning presets. Check out that chrome!

Inside the large, rectangular chrome housing at the rear is the round plate that makes the motorized tuner work. The drive motor is mounted near the front of the chassis, near the tuning knob. If you look closely at the chassis underside view, the motor is visible near center right.

800-B Versions

Stamped on the back of the metal tuner plate is the date February 7, 1947. There were two versions of this radio, the original 800-B and a revised model 800-B6. Mine is an 800-B6 and I believe this later version is more common.

The revisions provided more flexibility in programming the automatic tuning pushbuttons. They also reduced 60-cycle AC line "hum" in the receiver's audio. In early sets, the 0D3/VR150 voltage regulator tube is located next to the pair of rectifier tubes on the power/audio chassis. In later sets, that position is occupied by a tall metal-cased capacitor and the voltage regulator tube has been moved to the center of the chassis, next to the 6SL7 inverter tube.

An Authentic Speaker

One year after buying my 800-B, I finally located an original 15-inch coaxial speaker, shown below.

  

My "new old" speaker sounds good, and would sound even better with a good enclosure. Maybe I'll get around to building one some day. Meanwhile, the Scott is serving as the world's greatest shop radio, and I listen to it just about every day.

One good Scott deserves another . . . . Two years after getting my first 800B, I found another one in a cabinet with a record changer and television. A photo appears below. See Scott 800B6 TV/Radio/Phono for details.

©1995-2017 Philip I. Nelson, all rights reserved