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Fisher 90-R AM/FM Tuner

Discussion in 'Fisher' started by audmod01, Nov 3, 2018.

  1. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    I have a Fisher 90-R AM/FM Tuner that I am checking out. So far the AM works OK as does the EM84 (although dim). On FM there is no indication of reception. I had to replace one 6JB6 IF tube to get the AM working. The V5 6BH6 was weak and I replaced it with a better used 6BH6 that I had on hand. There is no reaction from the front end on FM. I tried a different 6AQ8 from a working radio to no avail on FM. There is not any closure on the eye tube on FM at all.

    I plan to order a few tubes, but in the meantime, does anyone have a scanned copy of the Owner's Manual for the 90-R?

    Thanks in advance.

    Joe
     

     

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  2. mhardy6647

    mhardy6647 AK Subscriber Subscriber

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    52,687
  3. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    Yes, I do have a copy of the original Fisher service manual. I have been working on adding component values to the schematic so I don't have to keep looking back to a parts list. The service manual is pretty decent overall. All the voltages are shown on one page with a chart. All the alignment information is on another page with a chart.

    I just ordered a set of tubes for this tuner to try, just in case there is a defective tube that still shows conduction, though weak.

    I have an 800-C receiver coming so I also ordered a quad of matched Tung-Sol 7591 output tubes for that on the same order.

    I did some cursory ohm-meter checks of the primary and secondary windings of the AM and FM IF transformers. So far they appear to be OK. The unit has normal B+ to all plates and screens so that much is operational and as I said, AM works OK.

    Joe
     
  4. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    I should have connected the tuner to an audio preamp/output amplifier! It had FM audio all along, but the FM signal level would not show up on the tuning eye tube although the AM did. It turned out that CR1, which is inside the L 11 can along with CR2, was open! Both diodes just clip into some holder contacts and are accessible by pulling the top of the can off. The top is just an interference fit and comes off easily - no need to remove the assembly from the chassis or anything drastic like that. I pulled a 1N4448 diode from a bag of parts I had removed from some solid state power supply and put it in place, replaced the cover and gave it a try. Now the FM tuning clearly shows up on the tuning eye tube. I had looked carefully at the terminals underneath L 11 and spotted R30 and R31. When I attached my voltmeter to their junction I could see that there was no voltage varying at that location. With CR1 being open, there was no way for a voltage to ever get to the eye tube from the FM signal level detector consisting of CR1 and CR2 plus associated resistors and capacitors.

    Next I need to listen to it on the air and tune in some stations. If there is any scratchiness in the ganged tuning capacitor, getting to it is more involved than later models. On this front end you have to un-solder some wires on the top side of the RF compartment cover in order to remove it by also removing some nuts securing studs from the underside. Then you can get to the pivot points of the capacitor shaft to clean and lubricate them.

    Evidently the OEM tubes that are still in the unit are not in too bad condition. When I replaced one IF amp tube the AM began to work. I did replace one other IF amp tube in the FM IF and it all seems to work pretty well so far.

    Joe
     
  5. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    Here are a couple of pictures. It is not too pretty - the front panel has rust spots a number of places where the corrosion of the steel underneath the brass plating has leached through. At least it works OK now. The lamps in the window to the left are burned out - may replace with LEDs and series resistor. The OEM lamps are very tiny - probably not readily available.
    90-R front web.jpg
    90-R top web.jpg
    Joe
     
  6. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    52,687
    Cool e-nuff! Congratulations -- even the most ancient of the Fisher tuners were... very good tuners. :)

    There's an 80-R here, btw. Works fine and is in pretty good shape, too. Almost disturbingly tightly packed in the "back office" is the 80-R :p

    [​IMG]DSC_9821 by Mark Hardy, on Flickr
     

     

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  7. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
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    How does the Heath compare to the 80-R?

    Joe
     
  8. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    52,687
    The Heath is OK, the Fisher is better than OK - speaking strictly sonically.
    Neither is in use, as you can see.
     
  9. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    That evaluation of the Heath tube type tuners agrees with my experience also. They were adequate, but could have been much better than they were. I had better results with my Dynakit FM-3 tuner, which had excellent sound. I later modified the Dynakit FM-3 for even better sound. I built it from kit in the 1960s and still have it to this day. My best Fisher tuner right now is the MF-300 paired with the RK-20 ultrasonic remote control. Beyond those two tuners my best ones are Kenwood KT-7500 units. The Fisher is as good as the Kenwoods and is basically the same circuit-wise as a Fisher FM-200-B.

    Joe
     
  10. fred soop

    fred soop Super Member

    Messages:
    1,990
    An engineer at Collins Radio in 1968 suggested that Scott tuners were much "hotter" than Fisher, but the reason was never explained. As I mentioned on another thread, I tested my Fisher 600-T and Heathkit AR-15 side by side from both sides of the same antenna splitter. While the Heathkit had much better specs, was a newer design by 3 years, and had an FET front end with 4 gang capacitor, neither unit proved clearly superior in my testing. They would both receive the same 60 stations with some being slightly better on one unit and some better on the other unit. A 25 year newer Harman-Kardon Citation 23 tuner will only receive 6 additional stations and those were all adjacent channel, made possible by using the high selectivity mode on the tuner. They were all noisy enough that one would not listen long term, so this unit is really no better.

    With the extremely poor selection of radio stations today, one might be better off to forget the tuner and stream from a phone.
     
  11. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    Fred;

    Many early transistorized FM tuners had poor performance dealing with a more crowded FM band. More stations even with the recommended regional distance spacing recommended by the FCC led to both alternate and adjacent channel reception issues. Cross modulation was an issue with many transistorized tuners for years. Only tuners that incorporated special narrow IF bandwidths could deliver the best reception of all stations that could be received without interference. Some solid state tuners used special LC IF filtering that was extremely difficult to align and was mostly done only at the factory. The introduction of ceramic IF filters made tighter filtering easier to achieve, but even then test selection of filters was often required to achieve the best possible results. As you pointed out fringe area reception of any station can be not pleasant to listen to due to noise and airplane induced flutter etc. Today not many FM stations have music that is worth listening to.

    My main interest here was comparing tube type tuners. I was surprised how closely some of my Fisher tube type tuners perform when compared to my best transistorized FM tuners of much more recent manufacture. When comparing tube type H H Scott FM tuners to Fisher units of the 1960s, I found the Scott units not as good as claimed in the circumstances I was able to try them. However there are many variables in receiving stations that can cause observed results with any tuner to not be the best.

    One of my friends on the Yahoo FM Tuners Group says no tuner is worth $1K or more due to the lack of decent stations these days. I see many offered on the auction site for far more than that. In the end, much of what people will pay for a tuner is due to considerations beyond just what test numbers will explain or justify. People often consider intangibles in their decisions that satisfy their own needs or desires. I have one issue related to cosmetics of tuners that prevents me from buying most any tuner from the mid 1980s and up - black faces of tuners with white lettering. I have had cataract surgery and since my eyes now have artificial lenses, those type tuners do something strange to my eyesight which makes them very difficult for me to discern what each control or push-button's function is. Black lettering on white or bright background is what my eyes need in order for me to enjoy using a tuner without dealing with vision frustration. Such is life.

    I get significant enjoyment just from restoring older tube type equipment to useful condition again. It is nice to be able to repair things instead of throwing them away.

    Joe
     

     

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  12. fred soop

    fred soop Super Member

    Messages:
    1,990
    Yes, even with lack of good stations, nothing beats the appearance of a vintage Fisher tuner / receiver, tube or transistor.
     
  13. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    For any of you who may have a Fisher 90-R Tuner or a 500 Receiver, I see that both use the very tiny screw-in 6.3VAC@.15A lamps for function (Fisher calls them "Channel") indicators. These shine through red plastic translucent bars to provide a Red indicator on the front of the tuner/receiver. The Fisher P/N is I-588-120 and even the Sam's Photofact manuals do not show a generic type number for these lamps. On this Fisher 90-R tuner one has missing lamp socket (the screw-in part is missing). The screw-in part of the socket is apparently swaged to the insulator part of the back of the socket where there appears to be a small Fish-paper insulator with a tiny brass contact to touch the center contact of a lamp. One of the brass screw-in part of one socket has been soldered to the plated mounting bracket already. The sockets appear to be rather delicate.

    I removed one of the lamps and found a number 378 stamped into its metal base between the threaded part of the base and the glass portion of the lamp assembly. The overall dimensions of the lamp are: 0.5725" long and 0.210" diameter. Have any of you found a source for these tiny lamps? How about the sockets for them?

    I plan to search for some of the lamps and sockets. If I do not find a source for both, I will just build up an LED replacement for the lamps. Since all of the indicators are red, red LEDs would serve quite well.

    Joe
     
  14. rufleruf

    rufleruf AK Subscriber Subscriber

    Messages:
    1,116
    Joe,

    Can you post a picture? I got several bags of vintage lamps at a radio club sale.

    Matt

    Your 800-C is out on truck for delivery!
     
  15. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    I managed to find both the lamps and the sockets on the internet. The lamp is indeed a type 378 miniature rated at 6.3VAC@0.2A and fits a Type E5 screw-in socket. The socket mount will not be exactly like the original, but I can adapt it to work on the existing mounting bracket.
    378 Lamps.jpg
    E5 Lamp Sockets.jpg
    So new parts are available after all. At first I thought these were going to be some "Unobtanium" parts. The last time I dealt with any lamps so tiny they were alarm indicators for telecom equipment power panels designed to operate from either 24VDC or 48VDC. I ordered some of both.

    Joe
     
    Last edited: Nov 9, 2018 at 10:49 AM
  16. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    One issue on the 90-R that I dealt with this morning was that when switched to FM operation, the eye tube would close so much that the lit areas would merge and overlap in the center. There is a 22M ohm resistor that trims the amount of negative voltage to the grid of the eye tube. I found that a 10M resistor gave a more normal closure of the eye when tuned to a strong station. I have three new RCA EM84 eye tubes on order so I can replace the dim tube in this unit. This will also provide two extra new eye tubes for future projects if needed. I can keep the old EM84 for a tube to use just to test for a go-no-go check on other radios or tuners.

    Joe
     

     

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  17. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
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    I installed some new FM IF tubes and gave the unit a real test using my outside FM only antenna. It delivers reception worthy of a Fisher! It picks up weak stations well as local ones also. On a few local stations it does develop some cross-modulation which can be corrected with the Local station switch. AM works fine and having sharp and broad selectivity there helps in some situations. On FM the one station from Dallas that I like comes in great with no interference from the alternate channel local station 4.5 miles from my house. Of course the IF and Ratio Detector in this unit does not have a broad-band detector circuit which helps provide enough selectivity to avoid the adjacent channel interference. I like the eye tuning indicator over a signal level meter. The audio is well balanced and sounds great to my ears with no further changes for now.

    Joe
     
    Last edited: Nov 10, 2018 at 2:17 PM
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,821
    Location:
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    Joe; Check the # of the Ratio Detector. If it's like the ones in the 610 consolette or early 60's tuners, it can be replaced with one from a later unit (use a scrap chassis) with # ZZ50210-9. Fisher used this one in practically everything from 1962 on up.
     
  19. audmod01

    audmod01 Super Member

    Messages:
    1,236
    Location:
    Tioga, TX
    Larry;

    I may try my outboard WX MPX demodulator with this one with no detector changes to see how it works. I could always change out the ratio detector if needed. I have a couple of ZZ 50210-9 ratio detectors on hand if I should decide to change it out for a test. I also have the IF transformers, both AM and FM from a 610-ST chassis saved as parts. I managed to get one decent AC accessory socket from the 610-ST chassis too. Many tuners and receivers arrive with at least one AC socket on the rear busted because some idiot tried to push a polarized AC plug into the socket.

    The new EM84 eye tube looks really nice now.

    Joe
     

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