800-C Restoration

Discussion in 'Fisher' started by audmod01, Nov 12, 2018.

  1. fred soop

    fred soop Super Member

    Messages:
    2,135
    Bought mine at Hobby Lobby. Yes, the finish is fragile but even slight damage may end up looking better than the unpainted version. Also, the paint is an insulator so make sure that anything that needs grounding is actually grounded. Don't know if baking would help the durability. Baking is standard procedure with brass model railroad equipment.
     

     

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  2. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    Fred;

    Thanks for pointing to Hobby Lobby. I should have thought of them. We were only 1/4 mile from them today. However, I ran out of time and we had to start home - there were frozen food items in what we bought. I will check there next time we get back to that area.

    Joe
     
  3. fred soop

    fred soop Super Member

    Messages:
    2,135
    That's one of the problems in Texas. This time of year (suburban Chicago), we don't have to worry about frozen items in the vehicle. So far, we also don't have to worry about anything freezing that shouldn't, but that will change in a few weeks.
     
  4. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    On repainting the right end of the chassis, I found some Krylon foil metallic paint at Ace Hardware not too far from home and also bought a can of Ace store brand silver metal paint. At home I tried both on a sample chassis and found that the less expensive Ace store brand paint was ideal for the job, so that was what I used. It turned out quite well.
    Pwr Xfmr fully repainted 02.jpg
    Here you can see the results of the chassis end repaint and that of the repainted Pwr Xfmr end bell. This right end of the chassis now looks like it is well dressed for a concert.
    Pwr Xfmr fully repainted web 01.jpg
    Here is another view of the Pwr Xfmr after complete repaint, including the leaves.
    Can Electrolytics Mounted web.jpg
    Here are the can electrolytics permanently mounted on the chassis.

    I prepared some terminal strips to anchor the output tube screen grid bus wire. I took some parts from Antique Electronics Supply which had three lugs arranged vertically and used a needle file to remove the top two lugs. File cuts into the bakelite on both sides just under the second lug from the bottom produced gooves that when the part is bent slightly snap apart in a good clean line. A little more filing smoothed the end of the bakelite. Then they were mounted at each end of the studs for the output tube heat shield studs using 1/2" 6-32 hex standoffs and 1/4" 6-32 screws and internal star washers. The 22AWG bus wire was strung between the two terminal strips and then the B+ supply wire attached at the end near the chassis center and the 7W and 1W B+ resistors attached a little left of the bus wire center and each screen grid 100 ohm protection resistor attached near each output tube.
    Modifying Terminal Strip web.jpg
    This shows the complete terminal strip with three lugs and the two that get removed.
    Screen Bus web.jpg
    Here you can see the end terminal strips and the 22AWG Screen Grid Bus installed. I did not insulate the bus wire, so it has B+ on it during power on situations. Whether to insulate between taps is up to the restorer. Since I have been in the business for many years, I did not add insulation here.

    My next task is reconnecting all the components and wire to the new can electrolytics I just mounted.

    Joe
     
    HairySatchel and 1rebmem like this.
  5. 1rebmem

    1rebmem AK Subscriber Subscriber

    Messages:
    194
    Location:
    Wilmington, NC
    Nice work.
    The chassis painting came out really nice!
     
  6. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    1rebmem;

    Thanks for the compliment!

    After first soldering the appropriate ground lances of the can electrolytics: C98, C87 and C91, I began reconnecting wires and resistors. I have two Weller soldering guns: model 8200N and model D-550 which I employed at the same time to have enough heat to solder the can capacitor ground lances to the chassis metal. I had my sketch of the original wire colors and resistors with from-to notes. I worked on one capacitor at a time, rechecking my wiring and connections as each terminal was to be soldered. I completed the work about 1PM and decided to stop and take a picture and then create this post.

    While reconnecting the resistors to C87, I checked each one and had to replace R115, an 82K 1/2W due to increase in value up to 91K ohms. I also had to replace R117, a 22K 1/2W which had been lost (it is probably somewhere on my desk underneath my ICOM HF transceiver). I had a new replacement so I used that. Then I measured R120, a 2.7K 1W resistor and it checked at about 3.2K, so I bridged it with the old R114 which brought its value back down to about 2.8K ohms and installed it. Eventually I will get a new 2.7K resistor and use a 2W rated part. There is a .001 snubber capacitor that attaches to one ground lug of C87 and that was reconnected and soldered.
    Can Electrolytics Replaced web.jpg
    The black tubular capacitor with the yellow band is the one that attaches to a ground lug of C87.

    I have not yet done anything with the bias/preamp filament rectifier bridge and filter capacitor. That will be next, but will wait until tomorrow or so when I have had time to look through my solid state parts to locate a suitable bridge rectifier.

    Joe
     
    Last edited: Dec 5, 2018

     

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  7. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    Could someone provide a picture of the AM Loop Antenna bracket on the underside of the chassis? I would like to see just how it is secured to the folded in brackets of the main chassis metal. There is a shaft that serves as a pivot point for the bracket and the end protrudes through the main chassis on the right side of the chassis under the power transformer.

    Thanks in advance.

    Joe
     
  8. audmod01

    audmod01 Super Member

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    1,403
    Location:
    Tioga, TX
    I did not have a bridge rectifier suitable (only some 15 and 50 amp types), so I have some on order now from AES.

    Joe
     
  9. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    I have a question about the right back corner of the 800-C chassis. There is a round hole in mine which in other units I have see pictures of looks like it has either the smooth end of a shaft for the AM Loop Antenna bracket or possibly a simple snap-in hole plug. Would someone verify what is actually used there?
    Pwr Xfmr fully repainted web 02.jpg
    The hole in question is at the far right just under the power transformer.

    Thanks in advance.

    Joe
     
  10. ncwalz

    ncwalz AK Subscriber Subscriber

    Messages:
    123
    Location:
    Alberta, Canada
    I think that provides access to the bolt that secures the AM antenna bracket to the chassis. I will post a photo later today when I get back from work if that would help.
     
  11. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    ncwalz;

    Yes, please do. That is pretty much what I thought. At first I thought it represented the end of a shaft going through the AM Loop Antenna bracket. But after looking at a few pictures I found on the internet, I believe it is a hole plug that simply snaps into the hole. I am guessing that there is either a common blade type screw on the antenna bracket mounting posts or a Phillips screw that is visible through the hole when the plug is removed. I need to measure the hole to see what its diameter is.

    Joe
     

     

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  12. sgmlaw

    sgmlaw Well-Known Member

    Messages:
    650
    I've only glanced over this thread. But that chassis side hole is indeed to tighten up the ferrite rod bracket. They did not come with hole plugs, so I wouldn't worry about it too much.

    Otherwise, it looks like you are doing a nice job so far. Only caveat is make sure that those cathode resistors are metal films. Your outputs and power transformer will thank you for it if there's ever a problem.

    Oh, and if you are not installing a grounded line cord, those paper/wax suppressor caps on the floating ground and at the voltage doubler should absolutely always be replaced, with class Y and AC-rated ones, as appropriate. Those two can potentially hurt someone should they fail. I prefer metallized ones over ceramics, if you have a choice, for that same reason.

    Good luck on your project.
     
  13. ncwalz

    ncwalz AK Subscriber Subscriber

    Messages:
    123
    Location:
    Alberta, Canada
    01.jpg 02.jpg 03.jpg

    Hey Joe

    Here are the pics of my 800c which I purchased from a fellow AKer but haven't really looked at. There is indeed a cover over the bolt access hole. This is different from my 800b receivers which have a different square access hole and no cover.

    Hope this helps. Let me know if you'd like other photos.

    Norman
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    22,400
    Location:
    Glen Burnie Md.
    What's the Serial # on that 800c. That might provide a clue. I'll take a look at both of mine tomorrow when I get to the house....(Serials 10386 and 33xxx) and see if there are any differences. The 10xxx series is in the Executive I have, and the 33xxx is standalone.
     
  15. ncwalz

    ncwalz AK Subscriber Subscriber

    Messages:
    123
    Location:
    Alberta, Canada
    Are you asking for my 800c serial number, Larry?
     
  16. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    The serial number on my 800-C is 47223 D which puts it fairly late in production. The 800-C that ncwalz has is equipped with the hole plug like a number of others I have seen images of. I also noted the rectangular access hole on the 800-B units for access to the AM Loop Antenna bracket hardware. I believe the purpose is to allow tightening enough to keep the bracket and antenna from flopping about. With the right amount of tightness it should stay in position where the user leaves it. One thing about the arrangements on the 800-B and 800-C is that there is no way to rotate the loop antenna in a vertical axis to get the best reception or direction for stations. It all depends on how the receiver is positioned. In the 202-R, the bracket allows such adjustment which makes achieving best AM reception easier.

    I measured the hole and its diameter is 0.345" which is close to 11/32". Maybe a 5/16" hole plug would work. I will have to see what I can find. I suspect the screw and nuts used on the antenna bracket is either 6/32 or 8/32 hardware. I need to see what size hardware fits through the holes of the legs stamped into the chassis. From the pictures that ncwalz provided it appears that the OEM bracket has a tab that provides a stop for how far the bracket will rotate in a downward direction. The nut at the end of the screw through the bracket appears to be a lock-nut.

    Jpe
     

     

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  17. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    I took a second look at the 800-C chassis and see that the AM Loop Antenna bracket is 1 1/8" wide between the two tabs in the chassis where it is secured. The hardware used has to be 6-32 X 1 3/8" to provide enough length to have a lock nut on the end closest to chassis center. The screw head must face the right end of the chassis viewed from the front.

    Joe
     
  18. sgmlaw

    sgmlaw Well-Known Member

    Messages:
    650
    I can absolutely, positively assure you, these 800Cs never came from the factory with those hole plugs installed. Any you are encountering were added in the field by users or techs. It's always possible that some UL-obsessed factory service depot added them later, but I doubt it. I've seen far too many of these over the years, I've never even seen a part number for such a plug, and I know exactly what came in the shipping container from Long Island City.


    Fisher2.jpg



    This was not a beauty area of the product, these were never intended to operate open chassis (most all were in-cabinet or in-wall installations), and they would not have wasted the money on one few would see or could touch. On a ventilated tube chassis already full of holes, it makes no practical sense to be plugging any holes anyway.

    Feel free to plug the hole if you must, but you will not lose any show points by not doing so. I promise. On a full-bore 800C rebuild, that little adjustment hole is the last thing to worry about.

    If you reach the point where you are contemplating a fresh clamp to reattach the ferrite rod to the mast bracket, circle back to me. The one on the 800C is a little different from that on the 800B, so don't necessarily rely on the latter for guidance. Most of the clear originals dry out, crack, and break off.
     
  19. audmod01

    audmod01 Super Member

    Messages:
    1,403
    Location:
    Tioga, TX
    sgmlaw;

    I was able to find a nice 6-32 X 1 1/2" SS screw with a Phillips head and a lock nut at Ace Hardware. They do not have 5/16 snap-in hole plugs (their sizes stop at 1/2" on the smallest size). Hillman does make a 5/16" hole plug, but there are few on the market at reasonable prices. I found a few at nearly $10 which is excessive and was just for a qty. of 1. So, the hole will remain open.

    I did remove C95 in preparation for installation of the new bridge rectifier part when it arrives (hopefully in the mail today). I drilled out the rivet holding the spring clamp that held C95 in place. I took time to sketch the associated parts so that installation of new parts will go easier with less opportunity for errors.
    C95 Removed web.jpg
    I have some steel plate left over from a previous project that I can use to make a bracket. I temporarily placed the new SS screw and lock nut in place as seen here. The hole on the side of the chassis lines up perfectly for access to the screw head.

    For those concerned about C110 a .01 capacitor on the AC input and C104 a .01 capacitor in the secondary lead to the voltage doubler rectifiers CR6 and CR7, I do have and intend to install safety qualified metalized film polypropylene capacitors there. I ordered a large quantity of these from Mouser several years ago. I will be replacing them as I work on rebuilding the negative bias supply. Installation of safety rated parts in those locations is something I always do. It is much easier with C95 out of the way. I plan to loosen the power transformer so that I can remove the rivet head left after the removal of the clamp that held C95. I should be able to leave enough room for a board to hold parts for the EFB circuitry as well as new electrolytic filter capacitors to take the place of C95A & B.

    As for the clamps to hold the AM Loop Antenna to the steel bracket, I plan to use some good quality nylon black cable ties which have an prepared for fastening in place using machine screws. I never cared for the OEM clear plastic clamps which were parts that failed early even years ago. I may use some PVC pipe and associated parts to enclose part of the antenna instead of the original cardboard sleeve approach. There is a terminal for connection of an external AM antenna if the user desires. I do have an outside long wire antenna I can connect.

    Joe
     
  20. sgmlaw

    sgmlaw Well-Known Member

    Messages:
    650
    You didn't need to remove the clamp holding the bias supply filter.

    If I'm refinishing the power transformer on these, I will rivet in two terminal strips on either side of that bracket to hold axial replacements. The tranny covers the rivet heads and it is invisible. Do not go cheap on the bias supply caps. Any failures can be quickly catastrophic to the outputs. For decades I used Sprauge Atoms in these, but the prices got ridiculous and their quality went in the toilet. In more recent years I have been using 105c Vishays in there (601D108F050FP1), which are not cheap, but should take anything you can create in there. A very high quality axial electrolytic. You can bump the voltage values up a grade, but don't go berserk on added capacitance.

    As far as the bias supply rectifier is concerned, buy a bridge with a mounting hole, and you can mount it exactly where the old selenium stack sat, on the side wall of the chassis, as in the attached example from a 500C job (an early 2000s job with grounded cord set installed; do not use these orange drops with a stock unpolarized line cord). There is very little to be reworked if you keep the bridge in the same place.

    IMG_0913.jpg
     

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