Mating a Fisher 440 Amp to a 490-T Tuner

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

  1. audmod01

    audmod01 AK Subscriber Subscriber

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    I have a Fisher 440 Amp and a Fisher 490-T tuner/preamp chassis. The 440 Amp is similar to the amp which was normally supplied with the 490-T with the exception that the 490-T has only three 12AX7 tubes with their filaments in series as part of the cathode resistance of the 6BQ5/EL84/7189 output tubes. The 440 Amp was designed to have four 12AX7 tube filaments in series to properly load the cathode circuitry of its output tubes. Since a 12AX7 filament operates from 12.6V @ .15A that works out to be approximately 84 ohms with a 2W power rating. I believe I can add a resistor in series with the power from the amp chassis to provide the load the amp likes to see to the DC 12AX7 filament circuitry.

    Alternatively, I could re-wire the 490-T chassis to put one of the 12AX7 tubes of the multiplex circuit in series with that filament feed from the 440 power amp circuitry. The needed 84 ohm resistance can reside either in the power amplifier chassis or in the tuner chassis.

    I just submitted some orders for a set of EL84 output tubes and the 7487 driver tubes for the power amplifier chassis. I have enough 6AU6 and 6BA6 tubes on hand. I also had to order 12AX7s and a 6AQ8 for the tuner chassis. I have a 6AH6 that can take the place of the 6HS6 in the IF circuitry. The set came with the 6BE6 and the EM84-A eye tube so those are OK and check good on my tube tester. I am looking forward to getting this up and running to see how it sounds.

    One thing that is nice about these cabinet chassis is that they are usually quite clean compared to the component series. I have seen far too many component models that have had drinks spilled down inside them with the corresponding corrosion of the chassis.

    Joe
    Image 01.jpg
    490-5 face 01.jpg
    490-T chassis front 01.jpg
    490-T chassis surface.jpg
     
  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Great project Joe. I did a similar project here as well:

    http://audiokarma.org/forums/index.php?threads/junkbox-fisher-project.604064/

    The resistor will work (use 82Ω) or, consider adding the extra tube socket and adding in the missing 12AX7 that the four tuber had. One last option you could consider, is to simply modify the bias configuration in the power amplifier chassis so as to operate correctly with 3 tubes instead of four. This would consist of changing where the control grids are tapped into the heater string to produce the correct output stage current draw when only three tubes are used. The net effect of the change is that it would up the B+ across the output tubes by the amount of heater voltage originally dropped across the fourth tube, or the resistor you're planning on using.

    Good luck with your project!

    Dave
     
  3. audmod01

    audmod01 AK Subscriber Subscriber

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    Dave;

    Thanks for those suggestions. I need to check the wiring of the electrolytics to make sure that the power amplifier chassis does not have the wiring problem you mentioned in your other post.

    As a side note, I pulled some 12AX7s from my old H-K A300 integrated amplifier and discovered that H-K used Telefunken 12AX7s as OEM parts. One of four had been replaced by an RCA tube by one of my nephews years ago when I had given it to my sister to use. She eventually gave it back to me. I used it for several years as an amplifier for tuners I was using in my barn. I have some bookshelf speakers out there that are currently being driven by the X-101-C that I restored a few years ago. I think I will use this Fisher out there after I finish restoring and modifying the unit(s).

    I was also lucky to find some 7-pin miniature tube type shields that I had on hand. I had to install one on the Limiter 6AU6 in the 490-T which arrived with no shield for that position. I borrowed two 12AX7 shields from the 610-T chassis that I have on hand too to shield the phono preamp tubes. So with those tubes from the H-K A300 I have a complete set of functional tubes to run some tests. I even had two 6AQ8 tubes from the Fisher 610-T chassis and borrowed one to use in the 490-T for tests. Now I just need to check the power supply in the 440 amp to see if everything there is good enough for an initial test. I have a nice powerful Variac I can use to slowly bring up the voltages on everything.

    The 12AX7s in the phono preamp circuits will have the same roll-off on the low end as you mentioned in your thread. I plan to eliminate that and allow full range low end response. I don't currently have a turntable in the barn but do have room for it. I am considering getting a Garrard AT-6 to use with it there. Larry might know if the AT-6 includes the AC switch that can turn the whole Fisher unit on if Automatic operation is selected.

    I even have some of the Fisher knobs left over from working on the X-101-C roach motel mangled unit, although I need the knobs for the treble and bass that are separate concentric types. I will eventually get enough new brass caps to make them all look good.

    The picture of the 440 amp makes it look quite dull and dim, but in actual fact, it is rather clean and bright. It does need a light cleaning, but overall it is nice and essentially corrosion free. I ordered a set of tubes for it from AES ostensibly for Dynaco SC-35 amps, but it has the correct outputs and driver tubes that are used here for a decent price.

    Joe
     
  4. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Joe; The "AUTO" switch is a separate switch in parallel with the Phono power. It will be incorporated in the console's schematic in the Power supply. The phono cord just plugs in after the switch. The 440A ('62 Electra) does NOT have provisions for the AUTO-off switch. Which doesn't mean that one could be modded in. Look in the 490T (Futura manual) for the wiring from the amp to the tuner (off-on switch), and back to the phono. Pins 3-5-7 on the 9 pin molex.
     
    Last edited: Jun 6, 2017
  5. audmod01

    audmod01 AK Subscriber Subscriber

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    Larry;

    I understand what you are saying. What I am wondering is if the Garrard AT-6 series of changers incorporate a switch which would allow that to be implemented. I don't have a schematic of the Garrard record changers that might be applied to know. I am not sure just how useful it would be for my use, but am just wondering if both the amp and the changer could support the feature. Perhaps I misunderstood the wiring of the Garrard changer which normally was supplied with the models that did support the feature.

    Joe
     
  6. gadget73

    gadget73 junk junkie Subscriber

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    They do. You'd just have to connect to it. Should be a 4 pin plug on the bottom with hot in, neutral in, ground in, and switched hot return. I have an AT6 in a console myself, though that one doesn't happen to make use of the auto-off.

    Even if it doesn't have the plug, no reason you can't simply tap into the switch on the motor side of it. Thats all the factory did.
     
  7. audmod01

    audmod01 AK Subscriber Subscriber

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    Gadget;

    OK, I know that my old AT-6 changer has a 4-position Molex plug that attaches to the mating connector on the changer. I might have to add a contact to implement it, but that would be easy to do. I can check ahead with my ohm meter to verify what connections are made for each position in the connector. So there is really nothing unique about which Garrard changer is used. I think the same may be true of Collaro or Dual models too.

    Joe
     
  8. dyche01

    dyche01 "Buy high. Sell low" Subscriber

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    Oooh, all this talk of mating Fishers is getting me worked up!
     
  9. audmod01

    audmod01 AK Subscriber Subscriber

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    I noticed on the 490-T tuner chassis that there is one hole in the chassis fitted with a metal button that snaps in place to close the hole. There is at least one variant of this type of tuner chassis (not the same chassis number) that has a 6GK5 7-pin miniature tube installed in that position. It looks at the presence of the19kHz pilot tone and turns on a pilot lamp to indicate FM stereo reception is active using a relay that has its coil in the plate circuit of the 6GK5. The 490-T and several versions of this chassis type normally uses an EM84 eye tube for the STEREO BEAM indication an FM stereo signal is being received and decoded.

    Personally, I like the aesthetics of the eye tube as opposed to a lamp being turned on. The more tubes the better! I may need to get a couple of EM84 eye tubes to keep on hand though.

    Joe
     
  10. audmod01

    audmod01 AK Subscriber Subscriber

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    As a follow-up, I was considering the unique 9-contact socket on the 440 amp chassis and how to mate it with the pendant cable of the 490-T chassis. The plug on the end of the pendant cable of the 490-T is a Molex connector. The 9-contact socket on the 440 chassis is such an odd part that no one has a mating plug for it. So what I am thinking is to use a pendant cable from the 440 chassis out say 1ft. to a mating Molex connector to interface to the 490-T pendant cable. The wires to the added pendant cable of the 440 chassis can go directly through each contact hole of the existing chassis socket and solder directly to the contact lugs underneath. That way no extra terminal strips or other hardware would have to be added under the chassis.

    Here is a picture of the strange socket connector on the 440 chassis.
    9-contact socket web.jpg
    Unless someone here knows of a source, I do not have any hope of finding one on the internet. None of my searches have turned up such an item.

    Joe
     

    Attached Files:

  11. audmod01

    audmod01 AK Subscriber Subscriber

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    I found some Molex 9-contact plug and socket parts on eBay and ordered them. The existing pendant cable of the 490-T tuner chassis has an older Molex 9-contact connector with rectangular contacts in it. I prefer to deal with connectors with round contacts, so I ordered the Molex items with .093 inch diameter elements which will be able to handle the currents involved with no problems. Cost is under $10 and shipping is free.

    Joe
     
  12. audmod01

    audmod01 AK Subscriber Subscriber

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    I received a note that the two Molex connectors and contacts are on their way today. I also received the tubes I had ordered from Antique Electronics Supply; (2) 7247 driver phase splitters, a matched quad of JJ EL84 outputs, (2) JJ ECC83/12AX&, (2) JAN 5749W/6BA6 tubes for the IFs in the tuner chassis. I have the needed 82 ohm 2W resistor coming from Mouser Electronics along with an assortment of COG/NPO disc ceramics for IF work if needed.

    Today I ironed the grill cloth that came for my E H Scott 800B and then took time to glue it to the baffle board and remounted the baffle in the cabinet. There was a diamond pattern brass grill in front of the grill cloth which had tarnished considerably. I was going to polish it and re-coat it with lacquer, but discovered the back side was identical in design to the front, so I removed the brass grill and turned it around. The back side was bright as new, so it is looking good now. The next step there will be to finish the mounting of rails inside the cabinet to position the radio tuner chassis above the front door that slides underneath the tuner chassis when open for tuning the radio. I will post some pictures once I get it all together.

    Joe
     
  13. audmod01

    audmod01 AK Subscriber Subscriber

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    Today I received an order from Mouser Electronics that includes the 82 ohm 2W resistor for the DC feed to the tuner chassis 12AX7 preamp tubes and some low pFd disc ceramic capacitors for repairing Fisher FM IF transformers. I took some time to trace out the wires from the 490-T chassis to the power amplifier. The connector is one made by Amp and has the designation AC-9 on a side of the connector housing. There are 3 molded ribs on one side of the white nylon plastic of the housing. These ribs identify contact no. 5 in the line-up. With the contact side of the plug facing you, the upper left contact is pin 1 followed clockwise to pin 3 at upper right, then down the right side to pin 5, then continuing clockwise to contact 7, then up the left side to contact 8. Contact 9 is the one in the center. Here is a list of the contact functions by contact number and wire color:
    1 = Blu 6.3VAC filament
    2 = Yel DC feed to Preamp 12AX7 filaments
    3 = Brn to AC switch
    4 = Blk chassis ground
    5 = Whi to AC switch
    6 = Red +170VDC input
    7 = Vio from Automatic Shutoff AC switch
    8 = Grn other side of 6.3VAC filament
    9 = Orn +275VDC input
    Fisher did not list the plastic plug housing with a part number. It is shown as P15 on the preamp/tuner chassis schematic but appears nowhere else in the service manual.

    Joe
     
  14. audmod01

    audmod01 AK Subscriber Subscriber

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    Today I took some time to investigate the 440-A to orient myself and learn component locations. I have some pictures of the underside of the chassis where I made notations of some essential components of the power supply that may also be helpful to others.

    Here are those pictures:
    440-A Under left.jpg
    440-A Under right.jpg
    Looking at a schematic is one thing, actual wiring is another. One thing I discovered while examining the chassis is that there is one capacitor, a .01uF @ 600VDC that is connected across CR4 in the power supply area. This capacitor is not shown on the official Fisher schematic, but is identical with C106 which is on the AC input circuitry. By connecting a .01uF across CR4 there is some protection provided to CR4 against voltage spikes and also some added noise immunity against any noise on the AC mains line coming to the set. Since these units were produced, many improvements have been made to AC component safety parameters and much better parts are available now to replace such parts. I will be removing both of these capacitors and replacing them with current safety approved parts.

    I am about to put together an order for new capacitors for the chassis. I am going to investigate using individual electrolytic capacitors to rebuild the existing electrolytic cans to maintain original appearance. I need to measure the dimensions of the cans to see if the capacitors available to me will all fit inside. I will develop a list of materials and report back on that if it looks possible.

    Joe
     
  15. audmod01

    audmod01 AK Subscriber Subscriber

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    I received the older Electra IV 9-pin plug used on the 440-A chassis from Charlie Ramirez recently. I was able to compare that plug to the 9-pin Amp plug used on the 490-T chassis. It turns out that the wire colors used for the 490-T cable are different from the cable used with the 440-A and its E48 tuner The 490-T plug is a square plug, while the 440-A plug is round. Function by wire color and pin numbers are different between the two tuner chassis. I will detail the differences in another report.

    Joe
     
    Last edited: Jun 30, 2017
  16. audmod01

    audmod01 AK Subscriber Subscriber

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    Today I took time to carefully disconnect the wires from the round 9-pin plug that Charlie sent me. Several wire colors were different on the cable for that plug, so It made sense to use the wires already on the 490-T tuner chassis. I clipped the Amp plug wires close to the plug and placed that plug into a zip-lock bag for possible future use. Then looking at both the Electra IV and VI models schematics I began to connect each wire coming from the 490-T tuner to the round 9-pin plug one at a time. When I had finished connecting all the wires, I plugged the tuner chassis into the 440-A power supply/amp chassis and used an ohm meter to check from the two AC plug prongs for the AC being switched off and on by the volume control power switch of the tuner chassis. That worked OK and I saw a normal resistance for the power transformer primary when the unit is switched on.

    Next I modified the 440-A chassis to provide for the DC filament feed to the tuner chassis which only has 3 12AX7 tube filaments wired in series. I had the needed 82 ohm 2 watt resistor on hand. I also had an extra two-lug terminal strip. I drilled out one rivet that holds C103 in place on the side closest to the 9-contact socket the tuner plugs into. I mounted the two-lug terminal strip there with some hardware. The 82 ohm resistor was wired to each lug of the terminal strip. Then the two yellow wires and 4.7K ohm 1/2 watt resistor that were connected to contact 6 of the socket were disconnected from there and moved to the terminal strip lug closest to the variable bias control R109 where one end of the 82 ohm resistor is located. A short yellow wire is added from the other end of the 82 ohm resistor and terminal strip to contact 6 of the 9-contact tuner socket. So the tuner only has the connecting plug on its interconnect cable changed and the 440-A chassis just has a modification to add the 82 ohm 2 watt resistor to make up the difference due to the tuner only having 3 12AX7 tube filaments in series.
    440-a Under Modified web.jpg
    I thought it best to do as few changes as possible for each chassis to keep the wiring changes to a minimum.

    Here is a list of the 490-T tuner wires by their original plug pin numbers with wire color indicated and their new connection to the 440-A round 9-pin plug/socket by pin number:
    Tuner Pin Wire Color/Function 440-A Plug Pin
    4 Black, Chassis & Filament Gnd 9
    5 White, 120VAC In to Pwr Switch 8
    6 Red, +170VDC B+ 7
    2 Yellow, DC filament feed 6
    9 Orange, +250VDC B+ 5
    1 Blue, 6.3VAC Filament & Chassis Gnd 4
    8 Green, 6.3VAC 3
    3 Brown, Pwr Switch Auto or Acc. socket 2
    7 Violet, Pwr Switch Normal 1
     
  17. audmod01

    audmod01 AK Subscriber Subscriber

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    I modified Fisher's illustration of the top of the 440-A audio out/pwr. supply chassis to show the schematic ID of each can capacitor, transformer and fuse.
    440-A Chassis Top.jpg
    I had ordered some Molex 9-contact plug/socket shells and contacts from eBay. After receiving them, I discovered that the contacts were all female, no male contacts were supplied with either connector shell! So this morning I put together an order from Mouser Electronics that includes 25 male contacts along with some Panasonic polypropylene coupling capacitors of several values all rated at 630VDC. I plan to wire the speaker connections of the 440-A back to the speaker selector switch on the 490-T chassis. I was all set to do that when I made the discovery about the lack of male pins for the Molex connectors - foiled again!

    Here is a list of the electrolytic capacitors I ordered for the 440-A & 490-T chassis:
    667-EEU-EE2E101S 100uFd@250VDC, qty. 2
    75-TVA1712 40uFd@450VDC, qty. 2
    667-EEU-FC2A101 100uFd@100V, qty. 1
    667-EEU-EB2E680 68uFd@250VDC, qty. 2
    667-EEU-EE2V470 47uFd@350VDC, qty. 1
    647-UPW2F220MHD 22uFd@315VDC, qty. 1
    667-ECA-2EHG100 10uFd@250VDC, qty. 1
    These items are coming from Mouser Electronics. There are other sources, this is just the one I used. The electrolytics are mostly Panasonic brand.

    So instead of doing the speaker connections today, I will go back to cleaning the 202-R escutcheon panel.
     
  18. audmod01

    audmod01 AK Subscriber Subscriber

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    Here is a picture of the 490-T and 440-A connected together except for the speaker wires.
    490-T 440-A together web.jpg
    Now I am waiting for parts.

    Joe
     
  19. audmod01

    audmod01 AK Subscriber Subscriber

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    I went into Sherman, TX and visited the local Lowe's store. They had the right size of white nylon cable clamps to secure the 490-T wires at the tuner chassis, so I bought some. They also had some larger ones that will work with most of the Fisher AM loop antennas that I have seen in their products. Those clear plastic cable clamps become very brittle and break at the slightest movement of the wires or cable they secure. White nylon cable clamps are very durable and last decades without getting brittle.

    Joe
     
  20. audmod01

    audmod01 AK Subscriber Subscriber

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    All the parts arrived for the 440-A power supply circuitry today, so I spent time attempting to get the internal parts of the 40, 40, 100uF can capacitor out. The two 40uF sections are rated at 450VDC and the 100uF is rated at 250VDC and has the lower leg of the voltage doubler function.

    I managed to get the bottom wafers and the 3 solder contacts removed OK. Unfortunately even with heat the rest of the internal parts refused to come out. I eventually tried everything I could think of and absolutely nothing was successful. In fact I eventually tried a reamer, followed with a 1/4" drill bit and my electric drill. That might have eventually have been successful, except that the drill bit managed to get cross angled to the side of the can and before I knew it, there was a gaping hole in the side of the can! This particular can electrolytic is a tall one at 3 1/2 inches tall. I have two other donor can electrolytics that are only 3" tall and have different marked capacitance values and voltages than this capacitor. However, I can use the cans and after finishing them print and place a label over the existing markings with the correct values.

    I did have success with the single cardboard insulated capacitor of 100uFd@250VDC rebuild. That one turned out quite well and is already installed in the chassis. I may take some pictures of the installed capacitor and put them in a post some time tomorrow.

    I stopped after dealing with the failed rebuild of the 3-section can electrolytic. I will try another day on that. I basically spent the entire afternoon working on it to no avail and I need the rest both physically and mentally before I tackle one of the donor can electrolytics to take its place.

    Joe
     

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