Mating a Fisher 440 Amp to a 490-T Tuner

Discussion in 'Fisher' started by audmod01, Jun 6, 2017.

  1. mrphilco

    mrphilco AK Subscriber Subscriber

    Messages:
    385
    Location:
    Ferdinand, IN
    Nope, no issues with using 8V rated LEDs on 6.3v. The reverse is not true - LEDs do not like overvoltage, and you can't run 6.3V LEDs on 8V. They will work for awhile, but will run very hot and die prematurely.
     
  2. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    Ron;

    Thanks for that information. I thought that would be true. It is nice to have confirmation. I might have to extend the ends a bit using some sort of sleeve. I did that on my 500C where I had the end pieces from the incandescent lamps and I attached them to the ends of the new LED types. That worked out well for a good fit when placed into the holders. I ordered enough of the LED lamps to have extras for future Fisher products.

    Many times when I order parts if, I see a price break I order more. The downside is that I am running out of room! I try to keep items in the original sacks they came in with the part numbers or specifications on the label so that I know at a glance whether I can use them for a given application. I keep some old parts removed which prove useful occasionally, especially power resistors with the values of wattage and resistance marked on them. I suppose most of us are somewhat of a packrat.

    Joe
     
  3. mrphilco

    mrphilco AK Subscriber Subscriber

    Messages:
    385
    Location:
    Ferdinand, IN
    ...indeed...

    I have found, and I believe I have mentioned this before in one of these AK Fisher threads, that the LED fuse lamps being sold by one particular vendor on the auction site are easy to modify in various ways. I've removed the end caps and soldered wire leads onto them to replace "meter" lamps in some receivers...unsoldered the end caps and soldered them back on again in such a fashion that it makes the lamps longer...removed the end caps, carefully ground off a small amount on each end and resoldered the caps in place to make them fit the early Fisher SS receivers...and even reduced their width a bit on each end and replaced the end caps with slimmer end caps from original Fisher tuner fuse lamps. They are quite versatile and stand up well to the punishment I have given to them.
     
  4. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    I took some time to examine the sockets for the festoon lamps that illuminate the dial glass on the 490-T. I discovered that at the end of the dial where someone had soldered in a small grain of wheat lamp with pendant leads, the receptacles or sockets where the lamp snaps into are broken. Both have a piece of the brown plastic broken away. I found one piece lying on part of the chassis the other one is just gone. The lamp replacements just pop out when an attempt is made to snap them into place. In looking at the design there is a rectangular opening in the dial plate metal that part of the socket protrudes through and terminates in a solder lug for attachment of the 6.3VAC feed to the lamp. This same socket part includes a mounting screw and nut that fasten the lamp socket pieces to the dial plate and at the same time provide a way to secure the dial glass using some small rectangular metal brackets that use some soft insulation that touches the outside surface of the dial glass.

    At first I thought I could use a conventional chassis mount clip-in fuse socket, but after seeing how this lamp socket is arranged and designed I don't think I can make a repair like I originally thought. Have any of you dealt with this situation on a 490-T tuner/preamp? If so, what was your solution? I looked at the 610-ST chassis I have and it has individual clip-in socket pieces that are mounted using a small hole drilled in the chassis to pass a screw so small that it takes a jeweler's screwdriver to deal with the screw head along with two insulating bushings to go into the hole and keep the 6.3VAC from shorting to the dial plate metal. the 610-ST uses the Long form festoon lamps (about 2 inches long). Its method of securing the dial glass is very different from the 490-T model.

    Joe
     
  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,760
    Location:
    Ball Ground, GA
    Joe -- In trying to envision what you're describing, I'm reminded of one unit I worked on where the lamps couldn't be snapped in either because the plastic was broken out -- almost as if an attempt was made to install too fat of a bulb. As with you, any attempt to install the correct bulbs simply had them fall out as a result of the broken plastic. I don't know if this is the case in your scenario, but my case, I was able to resolve the issue quite effectively by simply removing the one piece clip/electrical terminal at each end of each bulb, and reinserting them "backwards" (by 180 degrees). In this manner, instead of the bulb no longer snapping between the terminals which were originally oriented towards the outside of the receiver (with respect to the lamp), and the broken out plastic wall that was towards the inside, the bulb now snaps between the in tact plastic wall that is towards the outside of the receiver, and the terminal, which is now oriented towards the inside. With this repair, original style replacement bulbs simply snapped into place once again and were held firmly in place.

    I hope this helps!

    Dave
     
  6. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    Dave;
    What you described is exactly the situation I face with this one. I will try your method. It will be a simple matter to disconnect the wire from behind, turn the contact around as you suggest. There is still one side of the plastic wall that is unbroken on each holder end. The contact is only to one side of the lamp end when snapped in place. I think the scenario you described of someone trying to push a lamp with larger than original end caps is what broke the enclosed area of the holder.

    In the meantime, I ordered a chassis mount fuse clip holder just in case I have to do something more. I did come up with another possible solution using the fuse holder clip socket. Your method will take far less effort and should get it operational again quickly. I can always use the fuse holder for another project. Thanks much!
    Joe
     
  7. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    It only took a few minutes to get the contacts in the right positions to implement Dave's suggestion. After that the LED lamp substitutes plugged in with no other issues. I put a new strip of weatherstrip along each end of the glass and removed the encrusted old weatherstrip, put some heatshrink sleeving on the small metal tab holders to keep the glass dial in place and cleaned the glass one more time. Here is a picture of the result.
    Joe
    490-T Lamp Holder Repair web.jpg
     
  8. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    The Fisher XP-55B Speakers arrived today in very good condition. So delivery is now complete and I can plan a matching equipment cabinet. It is also time to get the Elac Miracord changer operational and check the system out completely.The speaker cabinets are a vinyl clad type so they are not quite as nice as they might have been, but they are very presentable and do not have lots of scratches, dents or peeling of veneer. The grill cloth is very nice and the Fisher medallions are all good and in place as they should be.

    Joe
    XP-55B Speakers web.jpg
     
  9. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    A Request:
    I have downloaded a copy of the Electra VI Owner's Manual from the console website. The faceplate illustration in the manual does not show enough detail. I am trying to determine what the control knobs for this model look like. Could someone who owns one take a picture of theirs and post it here so that I know what they look like?

    Thanks in advance.

    Joe
     
  10. mrphilco

    mrphilco AK Subscriber Subscriber

    Messages:
    385
    Location:
    Ferdinand, IN
    Joe

    Following a Google image search for the 490-T and looking at a few images, it looks like it uses the same type of knobs as a 500-B/800-B receiver or Fisher amps of that period.

    Just go to Google, type in "Fisher 490-T" and then click Images.

    In fact, one of the images I found in my Google search is from a seven year old AK thread:
    http://audiokarma.org/forums/index.php?threads/fisher-console-worth-restoring.285067/

    Go to post #20 of that thread and you will see a close-up view of the 490-T's face, with knobs.
     
  11. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    Ron;

    Thanks for the link to the images. It provided just what I needed to determine the correct knob type. I have bid on some knobs and also sent a request to a person I know who has thousands of knobs for vintage electronic equipment and sells them privately. One way or the other I will soon have knobs for the tuner/preamp chassis. I managed to order a new set of knob brights that are typical for a 400/500-C/800-C that will take care of all the knobs I will be getting to provide a full compliment for this unit.

    I took the chassis set out of its box again and hooked it to the XP-55B speakers I had just bought through eBay and it sounds great! Now if I can get the equipment cabinet and the changer going correctly it will soon be in the hands of my granddaughter.
    I know she will treasure it. You should have seen her eyes light up when I told her about it at her birthday celebration!

    Joe
     
  12. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    One final modification I am considering making to the 440-A amplifier chassis is to add 50uF@10VDC electrolytics across R99 and R102 which are 3.9K ohm resistors in the cathode circuits of the 1st. half of V12 and V13. This should improve the low end response of the 1st 1/2 of these driver/phase inverter tubes. As it is now, the low end response is still quite rolled off even with a 22uF@10VDC across R51 and R53, the cathode resistors of the line amp stages in the 490-T tuner/preamp chassis and loudness circuitry activated on the volume control there. I will observe for any instability problems just in case. There is a 220 ohm resistor between the ends of R51 and R53 to ground for each tube. That point is where the negative feedback is applied from the output transformer secondaries. I see a similar design approach in the 500-C, 800-C and X-202-B etc.

    It will only take a few minutes today to implement this change and test the results.

    Joe
     
  13. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    As I expected, adding the 50uF@10V (actually 47uf@10V) capacitors in the cathode circuits of the 7247 driver stages did make another incremental improvement in the low end. Now the bass control provides a good adjustment range without it getting excessive. A very nice sound indeed! There is no indication of instability either, so that seems to wrap up low end improvements nicely.

    Joe
     
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,760
    Location:
    Ball Ground, GA
    Joe -- Bypassing the cathode resistors in the line stage had the effect of raising all ships, so all that happened is that the NFB of the stage was increased slightly at all frequencies, producing little change in LF response. Increasing the value of the cathode bypass cap for the AF Amplifier stage in the power amp will improve matters only slightly as well.

    The real restriction is happening at the line stage with C44, 45, 47, and 48. Increasing these by a factor of 3 or 4 will do a world of good in your LF quest!

    Dave
     
  15. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    Dave;

    As usual, thanks for your input on this. I had already doubled the values of C44, 45, 47 and 48. I will go back and increase them more. I also increased the value of the .047uF coupling capacitors in the 440-A power amp. up to .082uF. Perhaps I should have gone higher there too. I notice that the grid resistors used at the 6BQ5 tubes are 330K ohms. Should those be reduced in value any? I need to go look at the tube manual and see what it says on cathode biased application for the 6BQ5 tubes in push-pull.

    P.S.: I just looked - the RCA tube manual says on 6BQ5 tubes 330K is the max for fixed bias and 1M ohm is max for cathode biased, so looks like the 330K ohm resistors are OK there.

    Joe
     
  16. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    I rechecked the values of C44, 45, 47 and 48 and I had increased them to .082uF value at the same time that I did the 440-A amp coupling capacitors to the grids of the output tubes. I think I have gone about as far as I can go on this. The further limitation is likely the audio output transformers. They are rather small compared to units that have flatter frequency response specified. Of course I am not using the amp with the original speakers that were used in the console, so there are only 8" drivers for the low end of the audio spectrum.

    Joe
     
  17. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,760
    Location:
    Ball Ground, GA
    Joe -- If you've increased all these caps as you have, then it might be time to run a frequency response test on the unit from the Aux input to the speaker output. Test at intermediate points as the results so dictate. That will really paint a clear picture as to how to proceed going forward if more work is needed.

    Dave
     
  18. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    I finally managed to order two of the tall Fisher knobs (the ones that look like two concentric knobs) from eBay and three more from a friend who is a member of the Dallas-Ft. Worth antique radio club. I have a set of new knob brights on hand to get them looking like new and the secondary brass rim on the large part of the knobs will polish up nicely with chrome polish. A light coating of clear lacquer will then protect the finish for a good number of years.

    I am getting ready to create the custom cabinet. I think a good approach will be to first build up a wooden framework to mount the record changer base and the radio/tuner chassis while having the 440-A power supply/audio out chassis sit below part of the changer. I made a template of the original opening for the changer from the plastic case it came in. The plastic case is quite flimsy and warps when picked up to move the changer. Once I get the fit of the changer wood base and the 490-T faceplate and chassis mounting worked out it will be easy to add sides, bottom and a back cover that will provide ventilation and access to the antenna and speaker connections.
    Joe
     
  19. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    32,363
    Location:
    Southern NJ
    Never been much a fan of plastic record changer bases. They are indeed pretty junky. A crappy plinth plus a sheet of cardboard makes a cutout template though.
     
  20. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    815
    Location:
    Tioga, TX
    Gadget;
    That is exactly what I did - cardboard to the rescue! If weather holds without rain I may make it to the lumber store for supplies and start by creating the base for the changer. I need to do that as it will butt against the front panel of the 490-T.
    Joe
     

Share This Page