Avery's "First" Maker: The TA-800

Discussion in 'Fisher' started by dcgillespie, May 31, 2017.

  1. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    1960: These were heady times at Fisher Radio Corporation. Stereo was the rage, the power war was on, and innovations were appearing overnight. Fisher was well into the process of quickly making its brilliant pivot from an emphasis on "separates" to emphasizing its all-in-one line of integrated amplifiers and receivers. And, it was a company bent on making "firsts" in the industry. It was the perfect time and environment then for the introduction of the TA-800.

    It's little brother (the TA-600) had been introduced a year earlier, and represented Fisher's first use of RCA's new high performance 7199 pentode/triode phase inverter driver tube. While otherwise conventional, the huge "first" of the TA-600 was its successful combining of a high quality full featured stereo integrated amplifier, with high quality independent AM and FM tuner sections, to allow for the reception of AM/FM stereo broadcasts. It represented the smallest Fisher footprint at the time for all the features it offered. Fisher however was always on the lookout for new technology that could improve it offerings, and it was coming fast and furious in those days.

    One item of significant interest was the introduction of the 7591 by Westinghouse in 1958. This little power house packed at least twice the power of a 6V6 into the same size bottle. All of a sudden, an honest 60 watt (total) stereo power amplifier could be had for little increase in space than a 40 watt 7189 design occupied. Add to that, the development of reliable high voltage silicon rectifiers that make possible the use of low loss cool running voltage doubler power supplies, and you have the basis for Fisher to create another "first" unit -- which they did: when the 7591 was registered with the EIA in February of 1960, Fisher wasted little time in releasing the TA-800 that year as well. With the trade off in space requirements between the power amplifier and power supply sections basically being a wash then, Fisher was ultimately able to capitalize on the firsts it offered in the TA-600, and added to them greater power output in the TA-800, using the same basic physical space as it's little brother occupied. With more power, new tubes, and new SS power supply, and it was another Fisher First! -- something Fisher took very seriously.

    With that quick backdrop in mind then, it's now 57 years later, and I've had one of these babies delivered to me personally by AKer Rob Thomas for restoration. You can find Rob's original thread on this unit here:

    http://audiokarma.org/forums/index.php?threads/ta-800-back-from-the-shop.769372/

    In view of the anticipated work the unit will need, and the relative rarity of these units as compared to other Fisher stereo receivers, I thought it best to start a new thread on the restoration of the unit. It is surely a thing of beauty.......... but what a sad sack it is operationally for a Fisher! Consider that as received:

    1. The AM Tuner doesn't work.
    2. The FM Tuner doesn't work.
    3. The Left Channel doesn't work.
    4. The Balance Control is weird.
    5. The center two output tubes try to red plate.
    6. The AC power switch has failed.

    Oh, and the AM Bandwidth/volume control/AC power switch assembly is so loose and sloppy that wires connected to it have broken off, as well as from the Balance Control next door as well. It appears that at some point in the past the volume control assembly was partially removed in an attempt to fix the power switch. Since the original switch is still in place, that effort was clearly unsuccessful. But when the assembly was reinstalled, wires to the loudness switch that were cut for its removal were never reattached, and the assembly was so sloppily reinstalled that wires either broke off from the movement of the assembly with use, or were simply never reattached. It's a mess to be sure.

    When I receive a unit, I first do an initial assessment by going completely through it and verifying the operation (or not) of every feature. Then, I troubleshoot to find out what the problem is for each concern noted. That's because there are problems that a simple recap restoration effort will not resolve. The assessment then allows me to determine what will be addressed by the restoration, and what needs to be repaired separately. Finally, all the tubes are performance tested so that then, along with the results of the assessment, a true picture of the restoration work required can be developed.

    That process played out well with this unit, as with troubleshooting, it was found that:

    1. While the AM tuner had two very weak tubes (causing that section to take notably longer to start working because their emission was so poor), the real problem of no reception was due to the loop antenna having no continuity. Some time in the past, the plastic mount for the loop antenna was broken. When that happened, one of the leads from the coil to the connecting terminals on the assembly was broken as well. Then, when it was glued back together, the glue accidentally covered up the broken lead so that the damage done was hidden. I was able to chip away at the glue, retrieve the lead and reattach it, and then able to pick up one of my late night listening stops: Radio Toronto, bad tubes and all.

    2. The dead FM section was found to be due to an open R29, a 68K resistor supplying screen grid power to the 1st IF amplifier stage. But while replacing it, and even accounting for two poor tubes in the FM RF section, reception was still very weak, with no deflection of the eye tube bars. That was traced to a defective Z3 IF Limiter Coil, that had the classic silver mica disease. That too has been successfully repaired, but even then, performance was still notably poor. The final issue identified was a very poor alignment of the entire IF strip, likely the result of some previous service effort that was attempting to "fix" the FM problems by aligning that section while Z3 was defective. With those issues resolved, other than a weak presenting (worn out) FM eye tube, the FM section now operates normally with plenty of sensitivity in spite of the weak RF tubes.

    The resistor would have been caught during the general component check of the restoration process. But replacing it and the bad tubes still would have resulted in poor performance of the section. Troubleshooting to find the defective limiter coil and poor alignment completed the picture for the total work required to bring the FM section back to life.

    3. The dead left channel was due to a shorted C114 coupling cap in the tone control amplifier stages applying over 100 vdc across the volume control. This saturated the pentode section of the left channel driver tube, causing no amplification of the stage. The normal restoration process will resolve this issue.

    4. The weird Balance Control operation is due to broken/shorted wiring to the control. With the other broken/severed wires to these controls, the physically loose assembly of the volume control, and the defective AC power switch, these controls will both be completely removed from the set, and cleaned up, tightened up, and repaired accordingly as a separate function apart from the normal restoration process.

    5. The center two output tubes are new TS reissues, which have been well established to require greater bias voltage to establish normal current flow. When this is coupled with a still remaining selenium rectifier in the DC Heater/Bias Supply, red plating of these particular tubes is inevitable. This will also be addressed with modifications outside of the standard restoration process.

    The items that were repaired as part of the initial assessment were done to present the best overall picture with regards to potential outcome of the completed project to Rob. After all, FM IF transformers that can't be fixed or an AM loop antenna that can't be fixed would change to course of the project considerably, either in outcome, or required expense and effort to achieve a desired outcome.

    With all the potential deal killers checked, assessed, and/or resolved then, the project was given permission to move forward so that the actual restoration could begin. As a result, tubes have now been ordered from Jim McShane, power supply caps ordered from AES, and I've reached out to Mark Oppat for a new power switch, although I'm still waiting to hear back from him.

    The standard recommendations of adding an AC line current limiter, output cathode resistors, screen stability resistors, and converting the old selenium rectifier to silicon will also be done. In addition, individual bias controls are being added, and Rob has also asked me to investigate the installation of EFB(tm) in this unit as well.

    So with the stage set, it's off to the races. A few pics are presented to get things started, and then I'll make updates along the way as progress happens, parts arrive, and modification plans develop.

    Dave

    BELOW: Early Fisher gear is some of the nicest looking gear!
    SAM_1975.JPG
    BELOW: The glue has been chipped away, the bottom coil lead retrieved, and reconnected to its terminal repair the antenna loop.
    SAM_1982.JPG
    BELOW: Removing the offending FM IF Limiter Transformer.
    SAM_1981.JPG
    BELOW: Removed from the set.
    SAM_1983.JPG
    BELOW: Inside the transformer, the coil's B+ lead was carefully unwound from its connection terminal, since it was the shunt resonant cap across the coil that was diseased.
    SAM_1984.JPG
    BELOW: .....and connected to a new terminal installed in the unused 4th terminal location. This way, connection to the coil could still be made, but the old resonant cap in the transformer would be out of the circuit.
    SAM_1985.JPG
    BELOW: Reinstalled, good as new. Note the new silver mica resonant cap installed between the new terminal and the one opposite to it. All the connections originally installed on the third terminal have now been moved over to the new terminal, and the old terminal is bent over underneath the new resonant cap.
    The transformer now produces a very sharp and defined peak as it should when aligned.
    SAM_1989.JPG
    BELOW: This 68K resistor (R29) shows infinite resistance. It is simply open. Not burned open. Just open. I have seen this before with Fisher and other manufacturers as well. Every now and then, they would have to source what history has now shown to be a lower quality piece to maintain production levels. It was not uncommon for resistors of this type manufacture to go completely open as this one did.
    SAM_1986.JPG
    BELOW: It was replaced with this NOS piece taken from storage that was held in a vacuum sealed bag.
    SAM_1987.JPG
    BELOW: Broken loudness tap wires.
    SAM_1971.JPG

    A couple more pics to follow.
     
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  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    BELOW: Look carefully. The ground lead to the third terminal on the right of the rear balance control is broken as well.
    SAM_1972.JPG
    BELOW: Broken leads to the loudness switch as well.
    SAM_1973.JPG
    BELOW: It's hard to know when the last time was that this unit operated properly, but here is where we start. this pics was taken shortly after I started to disconnect the leads of the defective Z3 IF Limiter Transformer.
    SAM_1980.JPG

    And with that, the actual restoration can now get under way......

    Dave
     
    Last edited: May 31, 2017
  3. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Great Thread Dave, will be watching with interest! That's a very pristine unit cosmetically. You have your hands full on this one but we know it will turn out perfectly.... Al
     
    Last edited: May 31, 2017
  4. rufleruf

    rufleruf AK Subscriber Subscriber

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    Dave,

    Excited to follow this thread - I have two of these to fix some day.

    Post a picture of the power switch. I have some spares.

    Matt
     
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  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Hi Matt -- It appears to be the kind that mounts with three tabs into the rear volume control cover (as opposed to the type that slips over it) as seen here:

    SAM_1991.JPG

    If you got a spare, I know it would make Rob one happy camper! Still no response from Mark, but I know that's not particularly unusual for him. If you have a switch for the project, please PM me to let me know!

    Dave
     
  6. gadget73

    gadget73 junk junkie Subscriber

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    I may have a usable switch. I used some of the VC parts from my scrap TA-600 to fix my Pilot, but the switch was not one of them. I think the Fisher switch is actually in the Pilot, but I should have the single section original Pilot one around somewhere. I'll check when I get home.

    I've definitely seen the "twiddle with the screws" alignment efforts in the past. I have a CB that someone had messed with every single adjustment inside trying to make it receive again. It took me a not inconsiderable amount of time to get it aligned correctly again so I could finally diagnose the real problem, a dead RF amp transistor. Finding and fixing that would have been very simple if the rest of the thing hadn't been so completely messed up.

    I've also run into the open, undamaged CC resistor in an IF strip before. Most of the ones I had were plate resistors, but same sort of thing. No tuner, no voltage, no signs of any sort of damage or abuse.

    Also, small detail / history question. You mentioned that Westinghouse introduced the 7591 in 1958, but it wasn't registered to the EIA until 1960, and Fisher also didn't make use of it until that point. Did tubes have to be registered before manufacturers could make use of them, or was that 2 year period used by Fisher for development, etc?
     
  7. Rob Thomas

    Rob Thomas AK Subscriber Subscriber

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    Thanks for the write up on the unit Dave. Looking forward to hearing her sing!
     
  8. larryderouin

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

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    The broken antenna mount on the TA-600 and 800 isn't unusual. They get considerable heat from the 7189's on the 600, and I can imagine the greater amount of heat from the 7591's. This is not a receiver that I would use the EH7591's in unless it was a last resort. Everyone that I've seen has had the mount snap in approx the same place. Which is probably why FISHER installed a sticker on the antenna which read "DO NOT USE AS A HANDLE"! People don't read, and will grab the 1st thing that pop's out of the cover that is 1/2 way cool. If you remember from my TA-600 rebuild, I bridged the broken pieces with a piece of 2" x 2" perf board cut down to fit the mount and used 2 part Marine Epoxy. Which gave it considerable strength, but STILL don't use it as a Handle. The wires were also broken off next to the rod windings so i had to take a turn or two off the rod to get them to attach to the leads.



    [​IMG]

    I also noticed that the 7189's had a tendency to emulate the leaning tower of Pisa. So EL-84 retainers were installed to correct this tendency. I doubt the 7591's would do this, but ask Rob to keep an eye on them, and the antenna mount.

    [​IMG]

    Retainers link http://audiokarma.org/forums/index....e-tube-retainers-already.573073/#post-7527448

    For the 7591's These will work quite well. This type is used in the Sansui 1000A.
    https://www.tubesandmore.com/products/tube-clip-octal-sold-individually
    https://www.tubesandmore.com/products/tube-clip-belton-octal-sold-individually

    Sorry for the threadjack Dave. I thought it was relevant to the thread.

    Larry
     
    Last edited: Jun 1, 2017
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  9. Rob Thomas

    Rob Thomas AK Subscriber Subscriber

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    Thanks for the post Larry. I like your mod to the antenna. Looks much cleaner than mine!
     
  10. larryderouin

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

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    No problem. The mount was a poor design from the standpoint of heat and lifting by the antenna. I could have extended the metal up some more and mounted the antenna to the metal like done on the "B" and "C" models. Why I didn't here is one of those unsolved mysteries waiting for Robert Stack to work on. I'm not sure about the 800's antenna but on the 600, the holes in the mount for the screws are actually slotted so you could rotate the antenna at least 90* horizontally by removing one of the two outer end screws and loosening the remaining outer and the inner end screws.

    Note the HVAC Aluminum tape on the end bells. I was experimenting with radiant heat retention and reflection and found a 5-7*F drop with the HVAC TAPE as shown. When I completely covered the end bell (to the screws) I got a further reduction to -10*F total. I did this also on my 1000A on all of the transformers which gave me a drop of close to -20* drop, due to the reflection of the radiant heat back out, and removal of the power resistors to a different mounting. I doubt you'll get more than 10*F drop with the 7591's (especially with EH's as the bottles are larger), more like 5*F due to placement, but any drop is better than nothing. A plate btwn the tubes and the transformers might work on the heat like the "C" models but I don't think there is room for a plate, as close as those tubes are to the transformers.
     
  11. RS Steve

    RS Steve Tube Junkie Subscriber

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    Interesting thread, I haven't used my TA-800 in a long time. It was restored by our famous banned AK member, and after Dave found very questionable work on my TA-600, I need to assess the TA-800 before using it again. Looking forward to Dave's opinion on the 800 since he liked the 600 so much.
     
  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Gadget -- I don't know if there was a specific waiting period or not, but I imagine that by registering it with the EIA, it then became a viable piece for product manufacturers to use in their designs, which then made it an attractive piece for others to manufacture. In other words, it gave it street cred.

    AKer rufleruf has kindly offered up a new power switch for a very reasonable price, so with that, all parts have been ordered now. Thanks Matt!

    Also got a note from Jim McShane yesterday indicating that the one tube he was waiting on to fill my order will be delivered to him tomorrow, and that as soon as it arrives and is checked out, the order will be on its way here.

    Dave
     
  13. gadget73

    gadget73 junk junkie Subscriber

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    Cool, now I don't have to try and search the black hole of spare parts.
     
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Progress:
    BELOW: With a new switch on the way, the volume control has been removed from the AM Band Switch assembly and cleaned up. Because of the hollow band switch control shaft, the volume control uses a long mini shaft. SAM_1999.JPG
    BELOW: The old switch is removed awaiting the new one. The receiver section was open of course, while the Auxiliary AC Receptacle side was fused on!
    SAM_2000.JPG
    BELOW: And lest we don't want Rob to forget what he's leaving behind, I offer "LED in Blue". They will gladly be returned with the set -- or, I do have target practice scheduled this weekend.........
    SAM_1998.JPG

    Dave
     
  15. gadget73

    gadget73 junk junkie Subscriber

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    While I appreciate blue glow in the right circumstances, this isn't it. At work, I expect to see a lovely blue glow when the radiation source is at the bottom of the pool. Not seeing that basically means I'm going to die, so its a welcome view. I would not want to look at it on the front of my TA-600, thats for sure.
     
  16. Rob Thomas

    Rob Thomas AK Subscriber Subscriber

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    Ughh. I never want to see those bulbs ever again. Still can't believe that self described "tech" put them in without my blessing. I'll be glad when the new white ones are installed.
     
  17. Rob Thomas

    Rob Thomas AK Subscriber Subscriber

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    Larry, I like that aluminum tape reflecting some of the heat. That's a great idea! I'm also hoping this unit is a good candidate for Dave's famous EFB modification and that should cool things down a bit.
     
  18. larryderouin

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

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    It should help a great deal if it is. I don't see how it wouldn't tho.
     
  19. audiodon

    audiodon Addicted Member

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    Great to see this thread
     
  20. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Don, good to see you! :) Al
     

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