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Any TA-600 mods or upgrades available?

Discussion in 'Fisher' started by idadude, Nov 18, 2018.

  1. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Just would like to know if there are any mods or upgrades for the TA-600 that would improve reliability, stability, and/or sound quality out there, besides upgrading the caps. From what I've read from other owners, this is a nice sounding unit, so I would not mind putting a little work into it. Thank you.

    Larry D.
     

     

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  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    9,765
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    Ball Ground, GA
  3. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Dave,

    I'd read about references to your thread on the TA-600, but I could not find it. Much useful information there for sure. I do appreciate you putting in a link to it. When I ordered caps for this unit I also ordered some for my 202-T which I would like to get re-capped before I send it to you to put in the multiplexer.
    I should have it ready to send after the first of the year.

    Larry D.
     
  4. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Where can I find a good schematic to print out for the TA-600? The couple I've found are not readable when printed. The print is too light and not distinct enough. Thanks!

    Larry D.
     
  5. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Nevermind on the schematic. Found a good/readable one. I'm now trying to trace out a lot of the caps & resistors that need removal or changing out as per Dave's thread.

    Larry D.
     
  6. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,979
    Location:
    Southern NJ
    Make sure you get the right one. There are five different series of this unit and the schematic differs slightly. The 500000+ ones differ the most from the others. I think they are all at fisherconsoles in good quality.
     

     

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  7. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Thanks gadget73 for looking out for me concerning the serial numbers. Mine's 21995, so I did get the appropriate schematic and I did find it at Fisherconsoles. I'm going to help a friend improve the sound quality of his after I get mine completed. He wasn't too impressed with his after he got it back from being recapped. He said his sounded good,but not great. I'm expecting different results.

    Larry D.
     
  8. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,979
    Location:
    Southern NJ
    Mine is a late version. It sounds really nice, but it depends what you're after. If the goal is extremely accurate sound with flat frequency response from DC to light, this is not your amplifier. Its very warm, has a lot of bump in the bass with the loudness on, and sounds a little rolled off up top. Very pleasing to listen to, but not what I'd call highly accurate. The tuner really does work nicely though if you're into radio.

    Its also not a particularly powerful amp. Fisher claimed it as a 40w amp, 20+20. Its realistically a 20 watt amp. Mine does 18 with one channel driven, or a little better than 9 per channel with both driven. Efficient speakers are a must with this one or its just not going to have the guts to drive them.
     
  9. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    I had a Pilot 245 and 232 that I put a separate screen supply into both of them and that opened up those amps so that the top end had a lot more sparkle and detail without any harshness. It was a kit I bought from Jim McShane. I wonder if this amp is able to benefit from something like that.

    L.D.
     
  10. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,979
    Location:
    Southern NJ
    I think the bigger issue is the large resistor between the output of the rectifier and the output trafo power feed. The voltage changes across that thing with load, so the plate voltage swings more than would be ideal. The phono tubes serve as a cathode resistor, and the voltage there shifts a lot too. Whenever I get around to rebuilding mine, I was thinking of subbing a voltage regulator for the big resistor to control the voltage drop in the plate supply and strap a zener diode across the phono tubes to keep the voltage there from shifting so much. I expect it will help without getting too invasive. I really don't want to modify it so much that it becomes a completely different machine. Its on the list, still need to order caps for it. I think it forgot the words a year ago now, and I've done nothing but move it a few times since then. I'm getting close to sick of moving broken stuff though, and winter is a good time to hole up in the shop and get things done.
     
  11. mrphilco

    mrphilco AK Subscriber Subscriber

    Messages:
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    Location:
    Ferdinand, IN
    I added the IBAM mod to mine when I restored it. I really need to replace one of the 12AX7 preamp sockets in mine (the socket in question is intermittent, and I've tried cleaning it to no avail) so that I can start using it on a more regular basis.
     

     

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  12. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
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    I plan to add the IBAM to mine also. I have a physically leaking can cap, so I do not want to even try and bring this amp up on a variac until that can cap is re-stuffed. I don't know if there are any other issues that need attention, but I will know once that cap is replaced.

    L.D.
     
  13. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    I took out the 40/40/20/20 can cap that was physically leaking and when I tested it at 42/48/20/20 it seems almost good. Most of the time when I test leaking caps they're way off the mark. This one's reasonable, but I'm going to re-stuff it anyway. I have a capacitor analyzer, so it was not abnormally leaky (electrically) and the ESR was fair, but new caps will be better.

    Concerning the new caps I plan to install 47uf Nichicons and 22uf Panasonics. I have several types of each value of cap that I can use. When I test them on my analyzer one type gets down to 0.00 leakage much faster than the other, but the other has lower ESR. Which is the better cap to use? Thought I'd ask in case anyone knows. Thanks

    L.D.
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,887
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    Nichicon UPW and UHE's series are the one's I've been using for all P.S. work the last ten years. Low Impedance. However, UKL's used in the Signal path are low leakage. All are rated for 105*C. The New LGS series seem to be ok for P.S. If you have UFW and UKW (Audio Caps) use them in place of the UKL's if you want. As for Pana's I'm not sure but IIRC the FC(I think that's the series) series are ok for P.S.
     
  15. gadget73

    gadget73 junk junkie Subscriber

    Messages:
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    Location:
    Southern NJ
    The stock caps would have had relatively high ESR and leakage compared to modern, so I don't know that either spec matters a ton. High temp and small physical size are probably more important for re-stuffing. Last cans I did was before I knew pencil caps existed and it was a PITA. I have several of the tall skinny Nichicons (UPW I think?) that I bought specifically to re-stuff some cans with. Haven't done it yet, but I expect it will be less annoying than trying to cram short stumpy caps in there like Jenga.
     
  16. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    gadget. IIRC the pencils are UCS series.
     

     

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  17. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Did get the 1st can cap put together electrically. Should have it together and installed tomorrow. Might try to bring the amp up on a variac to be sure I have things correctly wired before proceeding further. Would be nice to hear some sort of output from both channels at about 60-80 volts. Wish I had more time and drive to put into this project so I could get it finished. I'll just keep chipping away at it.

    L.D. IMG_3257.JPG
     
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  18. idadude

    idadude AK Subscriber Subscriber

    Messages:
    932
    Location:
    Meridian, Idaho USA
    Well, I was able to get back to the 600, re-install the can cap, and wire it back up. Brought the receiver up slowly on a variac and got it to play AM radio through both channels when I got up to 80 volts. Success! The 600 is a 'good one'. Didn't even have any hum I did have one of the electrical terminals break off of the bottom of the quad can cap. Glad I have a bunch of the terminal posts (in the pic), they saved my butt this time.
    Next part of the project is to replace the rest of the electrolytics in there. I guess I'll have to put in 10uf's in for the 8uf ones. I have the two 300 ohm resistors to put in there too. Would be nice if the weather stays a little warmer so I would want to go out into my garage and keep working on it.

    Larry D. IMG_1386.JPG
     

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  19. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,979
    Location:
    Southern NJ
    Just mind the wiring to the preamp section that is reversed on that one can cap. Dave discusses the particulars of that, as well as some lead routing and the over-worked resistor issues in that article linked somewhere in this thread.
     

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