Picked up Fisher Electra VIII console this weekend. Worth repairing?

Discussion in 'Fisher' started by grindfix, Dec 3, 2018.

  1. fred soop

    fred soop Super Member

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    Those rectifiers should be chassis mounted for heat sinking. Should be enough space around one of those vacant transistor insulators.
     

     

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  2. grindfix

    grindfix Full time hobby Subscriber

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    My plan was to remove small terminal strip right between two pairs of diodes and use the hole to bolt bridge to the chassis.
     
  3. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    WS1's are small 4x6 speakers in boxes that were used to expand stereo separation back then. Check out the XP series Speakers thread in this forum, and you'll find them in one of the 60's brochures.
    As to Questions 4 and 5, YES. I would bump the Minimum Voltages on C-9 & 10 to 25V. The new caps will still be physically smaller and they'll handle a bit more voltage.
    C19- 4.7uf x 400v.
    C7-C8: 22uf x 300v.

    The 6A Tabletops are fine. I misquoted the Amps on the one I normally use. The Rectron BR84 ( 583-BR84 ) is an 8 Amp Rectifier. As these units use less than a 800C/500c/400 from the outlet, even 4 amps is really overkill.
     
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Put a dab of transistor grease on the rectifier. Even tho it's overkill, It will get warm, so anything used to keep it cool is good. Where you want to put it is fine. With the amp in it's normally vertical position, it's at the top. Mine is fairly cool there. The warmest place is around the tubes (2 Ell80's and the 1 12ax7.) with the Transistor area running a close 2nd.
     
  5. grindfix

    grindfix Full time hobby Subscriber

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    What about C9/10 16uF? 15uf or 22uf?
     
  6. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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  7. grindfix

    grindfix Full time hobby Subscriber

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    I had similar selected but wanted to hear your suggestion.

    Tuner / Pre questions:

    1. What do you suggest for 5000pF in preamp? Films are not really an option.
    2. Do you know the source for dial glass foam tape?
     
  8. gadget73

    gadget73 junk junkie Subscriber

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    5000 pf is 0.005uf. 0.0047uf of whatever film you like should work, unless its a critical value in a tone circuit. If so, just parallel a 300pf across it.
     
  9. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    I used Yellow Axial .0047's in posit's C44, C45, C47,C48. 600V in the 1st one (AES has them). In the 2nd one I used Cornell Dublier DME series in the Same posits plus the .02uf(C12-13) and .01uf (C9-10) in the phono section from Mouser. Small Radial caps. And they do quite well in the 49T.
    .01uf 400v 5989-400V.01-F
    .022uf 400v 5989-400V.022-F
    .0047uf 600v 598-DPP6D47K-F
    All other Ceramics leave alone. FISHER was one of the manufacturers that used very good Ceramic caps.

    Foam for the dial face use 3/8 thick Weather stripping (for screen doors and Windows @ Home Depot.)
     
  10. grindfix

    grindfix Full time hobby Subscriber

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    Thanks guys!
    Order is placed. While I wait on parts to arrive decided to finish something I had parts for. Can you guess what that is?
     

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  11. gadget73

    gadget73 junk junkie Subscriber

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    looks like either new tone control PEC or the improved RIAA PEC.
     

     

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  12. grindfix

    grindfix Full time hobby Subscriber

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    Bingo! Fisher 400 Phono PECs.
    Question: I can either leave them together, on the same perf board, or can cut in the middle and then channels will be farther apart.
    Leaving them together will be more rigid and will stay put better but not sure if components can pick up interference from one channel to another. What do you think?
     
  13. thornev

    thornev Well-Known Member

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    I installed them separately and they're fine. Thorne
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    But the problem is in the 49T each of the stock sections are right up against each other and against the bulkhead with the RF amp Box less than 1" away, while the receivers have plenty of room for separation of boards. Leave it as 1 board. Easier to mount. Make sure the ground from the board to the chassis is VERY GOOD.
     
  15. grindfix

    grindfix Full time hobby Subscriber

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    Larry, I didn't mean to cause any confusion but this board is not for console preamp. It is for Fisher 400 that I've restored and modified over a year ago but never had a chance to do this phono RIAA EQ upgrade. Thank you for your research - I just installed socket bushings that I got from Mouser based on part # you provided. I have some small choke chassis from Allen organ that uses same type of bushings under chokes and those bushings have short metal sleeve inside rubber to bring screw to torque. I used those inside of new phono bushings. I think it is better then to rely on thread locker.
     
  16. gadget73

    gadget73 junk junkie Subscriber

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    I made two boards for my TA-600. I also used smaller parts to shrink the footprint as much as possible. My boards actually came out slightly smaller than the original Fisher part, though I sort of screwed up and got the leads in reverse order. I didn't build the tape EQ into it either, so that reduced the parts count somewhat.
     

     

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  17. grindfix

    grindfix Full time hobby Subscriber

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    Happy New Year everyone!
    With a week of delay due to Mouser's error both chassis are finally recapped.
    I decided to stuff preamp can and all other caps are mounted under the chassis.

    DC measurements:
    Left: 7mv
    Right: 102mv

    Bias across .75ohm resistors is around 26mv with the exception of one on the negative side of right channel is in 17mv ballpark. Left channel heatsink gets off-cold. Right channel stays cold. Sound output is uneven for obvious reason.
    My thought is to move transistors (both pairs) from side to side to see if the low bias follows the swap. If it does not, would indicate temp compensating diode issue, right? Then next step would be to implement Fred's bias adjust circuit.

    Thoughts welcome!
     

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  18. gadget73

    gadget73 junk junkie Subscriber

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    I won't claim to be an expert on this amp, or SS amps in general but my experience with them so far makes me suspect the bias difference isn't where the uneven volume is coming from. Might be worth poking around with the scope while feeding it signal to see where it becomes uneven. If its right at the first stage, suspect something in the feedback circuit being off value. It might be the louder channel that is the problem.
     
  19. fred soop

    fred soop Super Member

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    Low bias would be more likely to cause an increase in crossover distortion than an obvious change in volume. Crossover distortion would be more apparent at very low volume. 17 mV indicates there is a problem, but that is not so low as to cause extreme problems.
     
  20. grindfix

    grindfix Full time hobby Subscriber

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    I found it. Amp output is balanced. It turned out to be mostly because of the imbalanced preamp 12AX7 and some more due to 2.7M resistor being 2.4M in one channel and 3.4M in the higher one.

    B+ is to high so as filaments. Everything runs as specified with variac output of 110v. Thinking of wiring-in bucking transformer. I found this configuration:

    [​IMG]

    I was still concerned with 100mv DC offset in the right channel so I swapped transistors around since they are same part number. Bias evened out some between negative and positive side but still lower on negative.
    DC offset is 60mv. Good enough or I should look for that temp compensating diode replacement?
     

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