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 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 say more 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.

The faceplate is champagne-colored metal with a satin finish and 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, floating in space against a dark background.

The knobs are walnut-colored plastic with polished brass caps. Surprisingly, this set had all of its original brass caps. Most Fisher receivers of this age are missing one or more of them, 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 switches among nine different modes: Tape, Aux, AM, FM-AM Stereo, 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 has 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 has two AC outlets for plugging in an accessory such as a tape deck or phono turntable.

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

Tube Type Function
V1 6AQ8 FM RF amp, oscillator/mixer
V2 6AU6 FM 1st IF amp
V3 6AU6 FM 2nd IF amp
V4 6AU6 FM limiter
V5 6BA6 AM RF amp
V6 6BE6 AM converter
V7 6EQ7 AM IF/detector
V8 EM84A AM tuning eye
V9 EM84A FM tuning eye
V10 12AX7 Channel A phono preamp
V11 12AX7 Channel B phono preamp
V12 12AX7 Channel A tone control amp
V13 12AX7 Channel B tone control amp
V14 12AX7 Channel A voltage amp/phase inverter
V15 12AX7 Channel B voltage amp/phase inverter
V16 7591 Channel B power amplifier
V17 7591 Channel B power amplifier
V18 7591 Channel A power amplifier
V19 7591 Channel A power amplifier
V20 12AT7 Low pass and 19KC amp
V21 12AX7 38K synch oscillator
V22 12AT7 Audio amplifier

With technology that was cutting-edge for its time, the 800-B is still eminently practical for everyday use. When correctly restored, it will provide years of enjoyment.

So Many Standards to Choose From!

A friend of mine in the computer world used to joke that "the great thing about standards is 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 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 a note on the evolution of FM broadcasting bands, see 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 standard, offering 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 true high fidelity over the airwaves.

The 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. An advantage of this scheme is that it didn't require any new inventions or manufacturing techniques, although it did require a "Siamese twin" type of radio like the 800-B that could combine simultaneous FM and AM broadcasts. 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 poor man's equivalent would be to tune in the stereo broadcast with two separate radios—one FM, the other AM—but the differences in circuit design, speaker size and quality, etc., would make the experience less than ideal.

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 illustrates 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 to simultaneously broadcast both channels of a stereo performance in FM and AM. As the owner of such a station, I would have asked why, with an investment sufficient to run two separate stations, I earned only one station's worth of advertising revenue!

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. The FM-AM system soon faded into oblivion.

Although you can't receive FM-AM broadcasts today, the 800-B's high-performance design 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 prior owner replaced the selenium rectifier and aligned the FM tuner. Here is the chassis underside (this photo was taken after I did all of the upgrades described below).

The receiver needed a little cleanup. Perhaps the most satisfying step was removing the dial glass and washing years of grime from the back as well as the front. The dial lamps also shone brighter after a quick wipe. These parts are accessible after you remove the faceplate, which is 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 applying a coat of walnut-colored Minwax and buffing it dry, to even the color and bring back a little more glow. The gold ventilator grille in back showed minor discoloration that wouldn't clean off, so I gave it a fresh coat of paint, as well. Now the cabinet looks factory fresh.

All four of the 7591 audio power tubes have Fisher factory markings, so they are either lightly-used originals or replacements installed when you could still get Fisher brand tubes from the factory. Since they all tested strong, I left them in place.

The previous owner supplied a copy of the 800-B service manual as well as upgrade instructions from the "Fisher Doc," Al Pugliese.

Upgrading the Receiver

I had heard that these receivers should be upgraded to improve reliability and performance, so I ordered a Resto-pak from Al. The kit includes several capacitors and resistors, which are not hard to install if you have good soldering skills. I would not call this a beginner's project, however. Some components are in cramped quarters. If you have never done any soldering before, I suggest practicing on a simpler radio first.

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 800-B's performance.

Note: use 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.

If your receiver still has its original selenium rectifier, replace it with the bridge supplied in the Resto-pak. This safety measure also extends the life of your costly output tubes.

The next photo shows where I installed eight key components. First, I added four safety resistors on the cathodes of the 7591 output tubes. The 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 four new resistors are shown in red circles in a column at the right.

I also replaced the four audio coupling capacitors. These should be replaced even if your receiver is playing well, since the originals aren't very reliable. If one of them leaks high-voltage B+ current, it can cause damage. In the previous photo, the four new coupling capacitors are shown in red circles in a column at the left.

The trickiest part of the upgrade was replacing components in the MPX sub-chassis. This involved two steps: replacing old plastic capacitors for safety and (optionally) removing the 19-kilohertz filters. All of these are located close together, so if you opt to remove the filters, do that at the same time you replace the capacitors. Removing the filter components creates more elbow room.

The next photo shows all of the components that I removed. At bottom center is the power switch; more about that in a moment. 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. This capacitor probably would have worked, but I replaced it anyway to ensure the correct voltage in this critical part of the receiver.

Replacing the Power Switch—Twice

The power switch is a notorious weak spot in this line of Fisher receivers. Knowing that, I ordered a new switch and installed it when doing the original upgrade. After a few years of service, that switch failed, too. Grrr!

You can perform a crude "fix" by wiring around the switch so that the receiver is always on, then turning it off and on with a power strip. I wanted to keep the receiver original, however, so I ordered a new switch from Louis Utsumi at metalbone.net. Louis also sells Fisher upgrade kits.

The switch is mounted on the end of the dual volume control, with a shielded cap covering its terminals. The first photo shows the switch with cap in place.

Both the cap and the switch must be unsoldered for removal. You must also unsolder a short metal strip attached to the grounded shield that encloses the power leads. This shielding is important; it prevents interference from the AC line as the leads stretch all the way across the chassis. To simplify replacement, turn the switch so that it clicks in the Off position before removing it.

The next photo shows the switch after the cap has been removed.

Three 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. I recommend unsoldering the original wires rather than snipping them off, which might leave them too short to reach the new switch.

Before soldering on the new switch case, I pressed it onto the back of the volume control and worked the knob to make sure that the mechanical parts had mated correctly. In this photo, the new switch is in place.

Then I soldered the switch onto the volume control case, soldered the leads on the terminals, and tested the switch for correct electrical operation. Finally, I soldered the cap onto the end of the switch case and soldered the strip from the shield to the cap.

I used a small soldering gun to fasten the cases. A soldering iron may not provide enough heat. Don't get carried away with the gun, however. Apply just enough heat to create a secure bond without frying things inside.

Cleaning the Controls

If you have never done so before, now is a convenient time to clean the volume controls. Spritz a small amount (not too much!) of DeOxit or equivalent inside the control openings, then work the volume knob all the way back and forth a number of times. This should prevent the volume control from getting scratchy, intermittent, or unbalanced on one channel.

You can perform the same treatment on the 800-B's other front panel controls. Be sparing. Don't splatter cleaner all over the place, and wipe up any excess immediately. Wait overnight before powering the receiver back up, to let the cleaner evaporate completely.

Installing a CL-60 Inrush Limiter

One cause of switch failure is the initial "inrush" of current when you turn on the 800-B. You can alleviate this problem by installing an inrush limiter between the power cord and the power switch. When I ordered the new power switch, Louis also provided a type CL-60 thermistor, which is more than adequate for this purpose.

The first photo shows where the power cord enters the back of the chassis. I'll add the thermistor on one leg of the power cord. Notice the coiled metal shield near the rightmost leg of the cord; this carries the power leads to the switch on the opposite side of the chassis.

The thermistor is a black disc about the size of your thumbnail. The final photo shows how I cut the power cord and installed the thermistor between it and the terminal point where it was connected. This point leads to the power switch.

A thermistor is a special resistor whose resistance changes when it heats up. When cold, the CL-60 has a resistance of about 120 ohms. During the short time that it takes to heat up, its resistance drops to almost nothing, and the receiver gets a "soft start" instead of a sudden rush of current.

Take care to insulate the leads of the thermistor. Since it generates heat, mount it away from other components. Installing a thermistor isn't a bad idea even if your switch is currently working. The cost is about $1 and you can find them at suppliers such as Mouser or Allied.

Using Both Switch Poles

I made one last change to protect the switch. The original switch is a double-pole type. One pole switches power to the receiver and the second switches power to the AC accessory outlets on the back of the chassis. If you change the wiring so that both poles are used to switch the receiver, then you have less current traveling through each pole, and possibly longer life for the switch.

I mention this modification here rather than in a previous section because you can do it at the connections by the AC cord rather than at the switch. I installed a short new wire to provide power to the accessory outlets at all times. I also moved one power lead so that it supplies current to the power transformer (T1) rather than the accessory outlets. This diagram shows the original circuit and the modified circuit.

After making this modification, you'll have to manually turn on and off any accessory plugged into the 800B's rear outlets. That's a minor inconvenience in exchange for longer switch life.

Fresh Tubes, Anyone?

After making these modifications, I put the 800-B back in my office to resume service as my daily driver, but noticed that one channel seemed louder than the other. I brought it back into the workshop to test the tubes, and discovered that they all tested weak (and one was especially bad).

Not a big surprise. The tubes had been in the receiver for some time when I bought it, and they lasted for about another decade of frequent use. I think I got my money's worth out of them!

New 7591 tubes are not cheap: about $20 apiece when bought in matched pairs, or more if you're fussy about brands and matching. Eighty bucks for four new tubes might seem like a lot, but I don't regret the investment for a receiver of this quality.

You can read more about the 800-B and related Fishers 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.

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