INTRODUCTION
I have always had a soft spot for Fisher vacuum tube FM, FM/AM, and FM/AM Stereo MPX tuners and receivers. Of all the pieces of this type of equipment that I have seen over my lifetime or has come across my bench, it is the Fisher gear that never fails to impress. Further, within the Fisher line, I think their FM Stereo MPX gear was their finest hour. This is hardly to knock their lines of integrated, preamp, and power amplifiers (including those sections within their receivers). Rather, it is to highlight the fact that designing and building really good FM Stereo MPX equipment back in the day was no easy feat. If it were, why were so many pieces of this gear from other manufacturers little more than junk by comparison? There were some other good pieces to be sure. But taken on the whole, which includes sensitivity, selectivity, ease of tuning, stereo performance, and not to forget the shear number of various pieces they produced with these qualities, it would be hard to identify any other manufacturer who was so recognized for producing such superb reception equipment.
Today however, most of this equipment is at least 50 years old, which can create a number of potential issues, ranging from younger folks not fully understanding the equipment, to service issues, to the fact that the FM band is now vastly different from that which existed when this equipment was designed and produced. Add to that the potential indiscriminate use of inappropriate modifications to some pieces, and the result is that many folks may not realize just how well these units can perform when operating properly.
There is no doubt that FM broadcasting has deteriorated at many stations across the nation, let alone how you may question available programming. There is an Atlanta country station that has their signal processors and compressors wound up tighter than a drum -- so tight that I find it un-listenable. Their modulation level is 100%, 100% of the time. The pumping in and out of the signal is just gross. But there are still a couple of good stations here and that, coupled with the fact that I always want my equipment to operate the best it can (regardless of use time), keeps me ever looking at how to get the best from this equipment.
In large part, this is best accomplished by making sure that a given piece operates as it was intended to, while meeting factory specifications in the process. However, the usual restoration practice of recapping the electrolytic and film caps and replacing the selenium rectifier that works so well in restoring audio circuits -- and needs to be done in tuner circuits as well -- can leave a number of issues unresolved in tuner and MPX circuits. Also, there are some modifications (or practices) that can be used to greatly extend tube life, and others that will simply improve tuner operation. So, I thought I would gather them all together for a one stop presentation to the Fisher community. A few have been discussed before, but there are some new tricks included as well.
First however, as a baseline, it will be helpful to establish what a properly operating tuner/receiver acts like:
A. In major markets you will very likely be able to receive multiple stations per mHz across the dial. For units with Automatic Stereo Switching, a number may not automatically trigger stereo reception unless you live in the city or manipulate the antenna, but the vast majority of them will be very listenable in mono mode. But even in the country where I live, my dial is pretty well packed from one end to the other. My lab is in my basement at the end of the house that is fully underground -- as therefore is my simple dipole antenna as well. Yet even with this restraint, I routinely listen to stations 100 miles away rather easily, in good stereo.
B. For units with a tuning meter, typical strong stations will produce a signal strength of "4". It typically takes a very strong signal (residing close to the transmitter) to produce readings much over 4 after the unit has reached normal operating temp. For units with eye tubes, strong stations will close the eye to typically less than 1/8 inch gap when the eye is acting as a signal strength indicator -- except for the 400 receiver. When this receiver is set to FM mono mode, strong stations will close the gap such that the width of the gap is basically the same length as either one of the beams coming in from the sides. In MPX stereo, any unit with an eye tube that indicates MPX reception will typically close the beam to less than 1/8 inch on strong stations. Finally, contrary to popular belief, Fisher did not design the eye tubes to close (although some particular tubes will), and in fact, you don't want them to. First, once the beam closes, it ceases to indicate optimum tuning since movement of the beam can no longer be discerned. Secondly, if the beam overlaps, it causes the florescent screen to burn very quickly where it overlaps. The screen on these tubes already wears quickly enough, while overlapping just accentuates it.
C. The tuning action will be sharp (a defined tuning peak), but not touchy, and capable of distinguishing between two close stations (i.e. 200 kHz apart) easily enough.
D. Stereo performance will be clear and distortion free (no ringing sound), with very wide separation on material that is so recorded to display it, and non-finicky to tune on stereo stations of good signal strength. For units with automatic stereo switching, the design is such that it takes a fairly strong stereo signal to activate stereo mode -- this to ensure noise free stereo reception. Fisher notes the importance of using a good antenna in the owner's manuals for all of their units to ensure good stereo reception. It is much more important than that required for reception of mono FM stations.
E. Frequency accuracy will generally be quite accurate at the ends of the dial, but may show some acceptable error (<.3 mHz) in the mid-frequency range depending on model.
F. Of course, with these units all being built into a steel chassis that is partially coupled to the AC line, they require a reasonable antenna, and will typically receive nothing with no antenna attached if the bottom cover is in place (however, dedicated console tuner/preamp units will typically receive a few stations even with no antenna attached since the antenna connections are located above the chassis on those models). Generally however, a standard dipole will provide very capable reception in most locations.
If these qualities do not define how your Fisher tuner or receiver operates, then it likely needs attention. Reduced sensitivity, selectivity, tuning action, stereo performance, or excessive dial glass calibration error almost surely indicates that some attention is needed. It is my experience that most units in fact do -- because most people who sell these units at auction or otherwise either know they're not right and are selling them off, or just aren't impressed but have no clue that they aren't operating correctly. Also, there's a lot of these units that have had attempted repairs made through alignment efforts, but were left worse than before the effort was started, because alignment wasn't the problem. Personally, I have an 800C, FM-100B, and FM-200B in my own collection. Two of them were sold with glowing reports of their performance, while the third was understood to need some work. In reality, all had way, way more problems than their previous owners ever realized (or would admit to).
Beyond the basic restoration efforts, a complete restoration service for tuner/receiver equipment often takes specialized equipment and knowledge that many techs just don't have. If your unit does require more than basic service, make sure your chosen tech has the necessary equipment and knowledge to properly service vacuum tube FM Stereo MPX gear. Otherwise, it can result in an expensive disappointment.
Next time, we'll start getting into all of this. But for now, this should give you a good idea if your Fisher is operating as well as it should be.
Dave
I have always had a soft spot for Fisher vacuum tube FM, FM/AM, and FM/AM Stereo MPX tuners and receivers. Of all the pieces of this type of equipment that I have seen over my lifetime or has come across my bench, it is the Fisher gear that never fails to impress. Further, within the Fisher line, I think their FM Stereo MPX gear was their finest hour. This is hardly to knock their lines of integrated, preamp, and power amplifiers (including those sections within their receivers). Rather, it is to highlight the fact that designing and building really good FM Stereo MPX equipment back in the day was no easy feat. If it were, why were so many pieces of this gear from other manufacturers little more than junk by comparison? There were some other good pieces to be sure. But taken on the whole, which includes sensitivity, selectivity, ease of tuning, stereo performance, and not to forget the shear number of various pieces they produced with these qualities, it would be hard to identify any other manufacturer who was so recognized for producing such superb reception equipment.
Today however, most of this equipment is at least 50 years old, which can create a number of potential issues, ranging from younger folks not fully understanding the equipment, to service issues, to the fact that the FM band is now vastly different from that which existed when this equipment was designed and produced. Add to that the potential indiscriminate use of inappropriate modifications to some pieces, and the result is that many folks may not realize just how well these units can perform when operating properly.
There is no doubt that FM broadcasting has deteriorated at many stations across the nation, let alone how you may question available programming. There is an Atlanta country station that has their signal processors and compressors wound up tighter than a drum -- so tight that I find it un-listenable. Their modulation level is 100%, 100% of the time. The pumping in and out of the signal is just gross. But there are still a couple of good stations here and that, coupled with the fact that I always want my equipment to operate the best it can (regardless of use time), keeps me ever looking at how to get the best from this equipment.
In large part, this is best accomplished by making sure that a given piece operates as it was intended to, while meeting factory specifications in the process. However, the usual restoration practice of recapping the electrolytic and film caps and replacing the selenium rectifier that works so well in restoring audio circuits -- and needs to be done in tuner circuits as well -- can leave a number of issues unresolved in tuner and MPX circuits. Also, there are some modifications (or practices) that can be used to greatly extend tube life, and others that will simply improve tuner operation. So, I thought I would gather them all together for a one stop presentation to the Fisher community. A few have been discussed before, but there are some new tricks included as well.
First however, as a baseline, it will be helpful to establish what a properly operating tuner/receiver acts like:
A. In major markets you will very likely be able to receive multiple stations per mHz across the dial. For units with Automatic Stereo Switching, a number may not automatically trigger stereo reception unless you live in the city or manipulate the antenna, but the vast majority of them will be very listenable in mono mode. But even in the country where I live, my dial is pretty well packed from one end to the other. My lab is in my basement at the end of the house that is fully underground -- as therefore is my simple dipole antenna as well. Yet even with this restraint, I routinely listen to stations 100 miles away rather easily, in good stereo.
B. For units with a tuning meter, typical strong stations will produce a signal strength of "4". It typically takes a very strong signal (residing close to the transmitter) to produce readings much over 4 after the unit has reached normal operating temp. For units with eye tubes, strong stations will close the eye to typically less than 1/8 inch gap when the eye is acting as a signal strength indicator -- except for the 400 receiver. When this receiver is set to FM mono mode, strong stations will close the gap such that the width of the gap is basically the same length as either one of the beams coming in from the sides. In MPX stereo, any unit with an eye tube that indicates MPX reception will typically close the beam to less than 1/8 inch on strong stations. Finally, contrary to popular belief, Fisher did not design the eye tubes to close (although some particular tubes will), and in fact, you don't want them to. First, once the beam closes, it ceases to indicate optimum tuning since movement of the beam can no longer be discerned. Secondly, if the beam overlaps, it causes the florescent screen to burn very quickly where it overlaps. The screen on these tubes already wears quickly enough, while overlapping just accentuates it.
C. The tuning action will be sharp (a defined tuning peak), but not touchy, and capable of distinguishing between two close stations (i.e. 200 kHz apart) easily enough.
D. Stereo performance will be clear and distortion free (no ringing sound), with very wide separation on material that is so recorded to display it, and non-finicky to tune on stereo stations of good signal strength. For units with automatic stereo switching, the design is such that it takes a fairly strong stereo signal to activate stereo mode -- this to ensure noise free stereo reception. Fisher notes the importance of using a good antenna in the owner's manuals for all of their units to ensure good stereo reception. It is much more important than that required for reception of mono FM stations.
E. Frequency accuracy will generally be quite accurate at the ends of the dial, but may show some acceptable error (<.3 mHz) in the mid-frequency range depending on model.
F. Of course, with these units all being built into a steel chassis that is partially coupled to the AC line, they require a reasonable antenna, and will typically receive nothing with no antenna attached if the bottom cover is in place (however, dedicated console tuner/preamp units will typically receive a few stations even with no antenna attached since the antenna connections are located above the chassis on those models). Generally however, a standard dipole will provide very capable reception in most locations.
If these qualities do not define how your Fisher tuner or receiver operates, then it likely needs attention. Reduced sensitivity, selectivity, tuning action, stereo performance, or excessive dial glass calibration error almost surely indicates that some attention is needed. It is my experience that most units in fact do -- because most people who sell these units at auction or otherwise either know they're not right and are selling them off, or just aren't impressed but have no clue that they aren't operating correctly. Also, there's a lot of these units that have had attempted repairs made through alignment efforts, but were left worse than before the effort was started, because alignment wasn't the problem. Personally, I have an 800C, FM-100B, and FM-200B in my own collection. Two of them were sold with glowing reports of their performance, while the third was understood to need some work. In reality, all had way, way more problems than their previous owners ever realized (or would admit to).
Beyond the basic restoration efforts, a complete restoration service for tuner/receiver equipment often takes specialized equipment and knowledge that many techs just don't have. If your unit does require more than basic service, make sure your chosen tech has the necessary equipment and knowledge to properly service vacuum tube FM Stereo MPX gear. Otherwise, it can result in an expensive disappointment.
Next time, we'll start getting into all of this. But for now, this should give you a good idea if your Fisher is operating as well as it should be.
Dave