Fisher Model 800-B AM/FM Stereo Receiver (1962)

This gorgeous Fisher 800-B receiver contains some of the finest in AM/FM tube technology and it also personifies a fascinating bit of radio history. One of the first receivers to support true multiplex FM stereo (the system in use today), it also supports the obsolete "FM-AM stereo" system that was used briefly during the late 1950s and early 1960s. We'll have more say about these stereo systems in a bit. But first, the facts.

Description

Manufactured for only a few years in the early 1960s, the 800-B is one of the most collectible tube-powered Fisher receivers. It is part of a Fisher line that includes the 400 and 500 series. (You can read about my Fisher 400 on another page.)

The 800-B was available with an optional walnut cabinet, although many were sold as bare chassis and built into custom cabinets. Since there were fewer Fisher cabinets than Fisher receivers, original cabinets can be find hard to find, but don't despair. Each owner's manual for Fisher receivers gives detailed instructions for building a cabinet of the right dimensions. My 800-B came with its original cabinet, a selling point for me.

The faceplate is a champagne-colored brushed metal, with slightly raised lettering. All Fisher dials of this era look good, but the 800-B's is one of the most appealing. It has separate FM and AM sections, one on each side, with a magic eye for each tuner and the famous Fisher bird logo in the center. Lit with dual lamps on the ends of the dial, the green and gold lettering glows softly, seeming to float in space against a dark background.

The knobs are walnut-colored plastic with polished brass caps. Astonishingly, this set still had all of its original brass caps. Most Fisher receivers of this age are missing one or more caps, which fall off when the glue dries out.

The 800-B has 15 controls, arranged in perfect symmetry. The FM tuning knob is at the upper left, and the AM tuner at upper right. At lower right is the power/volume control. The middle knob in the bottom row is the mode selector, which can be switched among nine different modes: Tape, Aux, AM, FM-AM Stereo (more about this later), FM (mono), MPX Stereo, MPX Filter, Phono, or Tape Head. The remaining knobs control left-right balance, treble, and bass tone.

From left to right, the eight slide switches offer the following functions:

• High filter on/off
• Low filter on/off
• Channel reverse on/off
• Tape monitor on/off
• Mono/Stereo
• Phase reverse on/off
• AM bandwidth sharp/broad
• Loudness contour on/off

Designed to serve as the centerpiece of a complete home hi-fi system, the 800-B offers lots of connections in back. As you'd expect, there are terminals for FM and AM antennas, external ground, and one set of speakers. The speaker block allows the use of 4-ohm, 8-ohm, or 16-ohm speakers. Like some other stereo sets of the time, it has an extra speaker terminal for a "center channel" speaker, which mixes the left and right channels together.

Input/output jacks include several connections for a tape deck, phono player, and auxiliary device. Another set of dual jacks lets you connect an external Fisher Spacexpander reverberation unit. The rear of the chassis also has two AC line plugs for connecting equipment such as a tape deck or phono turntable.

The 800-B employs a whopping 22 tubes. Here is the tube lineup.

The 800-B includes a few features that are superfluous nowadays, but it is an eminently practical piece of equipment and can provide many years of enjoyment if properly restored.

So Many Standards to Choose From!

A friend of mine in the computer science world used to joke that "the great thing about standards is that there so many to choose from." Although only one stereo broadcasting standard is used today, the 800-B embodies a time when there two different, incompatible schemes. The obsolete "FM-AM stereo" system might have become the standard for stereo broadcasting, but we're probably lucky that it didn't. Let's see where it came from.

Introduced during World War II, FM (frequency-modulation) radio virtually eliminated the static which was the bane of AM radio. It also offered vastly superior fidelity. (For some miscellaneous notes on FM's early days, see Zenith G724, Crosley 146CS, Philco 42-350). During the 1950s, FM gained a solid foothold in radio broadcasting, becoming popular with classical music listeners and devotees of the new "hi-fi" craze.

The 1950s were also a time of experimentation in multi-channel sound reproduction. The first stereo records and players became available in late 1957, and today's stereophonic (two-channel) system became the standard, offering much greater realism than monophonic (single-channel) sound.

The challenge to the radio industry of the late 1950s was to combine these two factors—FM's superior audio quality and stereo's heightened sense of realism—to provide higher fidelity over the airwaves than ever before.

One solution, which eventually prevailed, was to encode both channels in a single FM signal. At the receiving end, the radio receiver decoded the signal into two channels and played them on separate speakers. This was known at the time as "multiplex" stereo, abbreviated as MPX.

An alternate, incompatible, solution was "FM-AM stereo," which broadcast one stereo channel on FM and the other channel on AM. This scheme required a "Siamese twin" type of radio that could receive simultaneous FM and AM broadcasts, but it didn't depend on any new inventions or manufacturing techniques. FM-AM stereo broadcasts were available in several metropolitan areas for a period of a few years.

Tuning in an FM-AM stereo broadcast was a two-step process. First you switched your radio to FM and tuned in the FM station for one channel. Then you switched to AM and tuned in an AM station to get the second channel. Finally, you switched your radio to "FM-AM," and listened to the two-channel broadcast. Operating in FM-AM mode, the Fisher 800-B plays FM mono through the left channel and AM through the right.

The FM-AM system was too complex and expensive to prevail over multiplex stereo. To receive such broadcasts, the radio needed to have two completely independent tuners and converters. The 800-B is a great example of this complexity. It has a double dial, two tuning capacitors, two sets of pulleys and cords, and all the electronics to independently tune FM and AM stations at the same time.

That complexity was echoed on the sending side, where the station needed two independent transmitters—one FM and AM—to simultaneously broadcast both channels of a stereo performance. As the owner of such a station, I would have been tempted to ask why, with an equipment investment almost sufficient to run two independent stations, I earned the advertising revenues from only one!

The nail in the coffin for FM-AM stereo may have been the inherently inferior sound quality of AM. Manufacturers tried to overcome this by making the AM sections of these receivers extremely high quality, with features such as variable bandwidth. Despite their best efforts, however, this system could never sound as good as one that provided both channels on FM. Consequently, the FM-AM system soon faded into oblivion.

Although you can't receive FM-AM broadcasts today, the 800-B's high-performance AM section makes it a very fine AM radio. It is also an outstanding stereo FM receiver, so it is practical and desirable radio to own, as well as historically interesting.

Supporting two incompatible stereo systems, the 800-B may be the ultimate manufacturer's hedge. No matter which scheme prevailed, the 800-B would remain viable! Some manufacturers took a different approach, equipping FM mono tuners with a jack for an external multiplex decoder, which allowed you to play true multiplex stereo provided you had a two-channel amplifier. If you are buying "stereo" equipment from the late 1950s, make sure you know exactly what you're getting.

Restoration

Since I got this set in working condition, I didn't do much immediately after buying it. The selenium rectifier had already been replaced and the FM tuner alignment adjusted. I did spend a few hours carefully cleaning it up and inspecting the set inside and out, however.

Perhaps the most satisfying cleaning chore was taking off the dial glass and washing away years of grime from the back as well as the front. The dial lamps also looked better after a quick wipe. These parts are accessible after you remove the faceplate, which is easily done from the front after pulling the knobs and removing two nuts.

Although the cabinet had no scratches or dents, I spent a little time wiping down the wood veneer with walnut-colored Minwax and buffing it dry, to even the color and bring back a little more glow. After that dried, I applied a light coat of orange oil, again buffing it after wiping off the excess. The gold ventilator grille in back showed a little discoloration that wouldn't clean off, so I gave it a fresh coat of paint, as well. Now the cabinet looks factory fresh.

Two of the four 7591 audio power tubes tested noticeably weaker than the others. These tubes are scarce and quite expensive now. Depending on who's selling a 7591, I have seen a single tube priced anywhere from around $20 to over $75! It's not surprising that owners would try to stretch as much life from them as possible, but I'd like this set to perform as well as possible. I replaced the two weak 7591s and kept the old Fisher originals as emergency spares.

The previous owner supplied a copy of the 800-B service manual as well as upgrade instructions from the "Fisher Doc," Al Pugliese. If you have a Fisher set that requires service, parts, or technical manuals, Al can probably provide what you need. He can be reached at fisherdoc@aol.com or 718-948-7489. His website is http://fisherdoctor.com/.

Replacing the Power Switch

About one year after purchasing the receiver, its power switch gave up the ghost. At first, the power would mysteriously shut off from time to time. Turning it back on would usually restore power. Eventually, the power switch stopped working completely.

I learned from other Fisher owners that the power switch is a notorious weak spot in these sets. The simplest "fix" is to wire around the switch so that the receiver is always on, then switch it off and on with a power strip.

I wanted to keep the receiver original, however, so I ordered a new power switch, as well as the 800-B "Resto-Pak," from the Fisher Doc. The Resto-pak includes parts and instructions needed to upgrade the receiver for safe daily use.

Note: use extreme caution when turning the chassis over for service. This receiver is heavy and you can easily damage the fragile tuning capacitor pulleys if you accidentally grab or bump them during this maneuver.

Replacing the switch is not very difficult. The switch is mounted on the end of the dual volume control, with a shielded cap protecting its four terminals. The next photo shows the switch with the end cap removed.

Both the cap and the switch must be unsoldered for removal. The switch is secured with little tabs in addition to solder. To simplify replacement, turn the switch so that it clicks in the "off" position before removing it.

Four color-coded wires are attached to the switch terminals. I made a sketch before removing the old switch, to ensure that I would install the new one correctly. There is not much slack in the wires, so I removed them by carefully unsoldering each one. If I had snipped them off, they might have been too short to reach the terminals of the new switch.

Before soldering the new switch on, you must press it firmly onto the back of the volume control and work the knob to make sure that the mechanical parts have mated correctly. I connected the wires to the switch terminals before soldering the switch to the volume control. This allowed a little more slack for attaching the four wires. Then I soldered the switch onto the volume control case and tested the switch for correct electrical operation. Finally, I soldered the cap onto the end of the switch case.

Upgrading the Receiver

Al's Resto-pak includes several components—capacitors and resistors—which upgrade the receiver for safe, reliable, high-performance operation. These are not hard to install if you have good soldering skills. I would not call this a beginner's project, however. Some of the components are located in quite cramped quarters, requiring some skill to replace. If you have never done any soldering before, I would suggest practicing on a simpler radio before tackling this project.

This project also requires the ability to read a schematic diagram and identify the correct parts on the chassis. Unlike many service manuals, the Fisher manual does not include an under-chassis photograph showing the physical location of all the components.

The most important steps are to replace unreliable old capacitors and the selenium rectifier, and to install safety resistors on the 7591 output tubes. Other steps are optional, but will improve the receiver's performance.

The previous owner had already replaced the selenium rectifier with a new silicon bridge, so I skipped that step. If your receiver still has its original rectifier, be sure to replace it with the bridge supplied in the Resto-pak. This is a safety measure and it also helps extend the life of your precious output tubes.

The next photo shows the four safety resistors installed on the cathodes of the 7591 output tubes. These resistors protect the receiver against damage in case a 7591 tube develops an internal short. This step is simple. You snip and remove a short wire leading from pin 5 to ground, replacing the wire with a 10-ohm 1/4-watt resistor.

The next step is to replace the four audio coupling capacitors. These should be replaced even if your receiver is playing well. The original plastic capacitors are not very reliable. If one of them becomes leaky, it can admit high-voltage B+ current to a place where it doesn't belong, causing damage. The next photo shows the new coupling capacitors in place.

Note: although all four coupling capacitors are .047 mfd in value, two of them are 250-volt and two are 450-volt. Follow the Fisher Doc's instructions carefully to make sure that you install the right capacitors in the right spots. The higher-voltage caps are physically bigger than the others, as the photo shows. The voltage and capacitance values are also printed on the components, of course.

The most difficult part of the upgrade was replacing components inside the MPX (stereo multiplex) sub-chassis. This work involved two separate steps: replacing old plastic capacitors for safety and (optionally) removing the 19-kilohertz filters. All of the components for both steps are located close together, so if you opt to remove the filters, plan to do that at the same time you replace the old capacitors. Removing the filter components will give you a lot more elbow room for replacing the caps.

The final photo shows all of the components that I removed. At bottom center is the power switch. To its left are three yellowish-silver electrolytic capacitors. At far right on the bottom are two pudgy red filter coils. Between the switch and the two coils are four resistors. Immediately above the switch are two small ceramic capacitors which form part of the 19-khz filter. Finally, the group at the top of the photo includes twelve plastic capacitors of various values. Most of the original capacitors are dark brown or black, as you can see.

The large orange capacitor is a recent replacement done by the previous owner. Although this capacitor would probably have worked just fine, I replaced it anyway, to ensure the right voltage match in this critical part of the receiver.

Final Thoughts

With the upgrade complete, I gave the receiver a nice long test on the workbench, then reinstalled it in the cabinet. It lives in my study right next to the computer where I do my writing. It's playing right now, in fact, and it sounds glorious!

You can read more about the 800-B and related Fisher receivers in an excellent article in the Winter, 1997 issue of Vacuum Tube Valley magazine. Back issues of that publication can also be purchased from Antique Electronic Supply.