Eico ST40.....

Discussion in 'Eico Place' started by Cogsinister, Oct 27, 2012.

  1. RWood

    RWood The future is not what it used to be Subscriber

    Messages:
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    Location:
    Richmond, VA
    Well first you have unlearn most of what you ever learned. Then scratch your head. Here's how I did it, following the manual, and it works. Note the bare wire running from the top terminal to the one below it:

    [​IMG]

    I also did a re-cap, here are some shots. The JJ can caps are fairly low cost, as are the white Mallory couplers.

    [​IMG]

    [​IMG]

    [​IMG]

    I also did the infamous Loudness mod, as well as the phono section mod. Lots of resources here for these fine sounding (but occassionaly confusing) amps.

    RWood
     
  2. jaguar06

    jaguar06 Super Member

    Messages:
    1,771
    I need to do the loudness mod on my ST-70 as the stock setup if truly faulty.

    I *have* been wondering about what we've discussed here as being maybe a "typo" in the screen-painted speaker hookup diagram on the back and in the book with regard to the positive/negative--I've found that the ST-70 *requires* me to flip that "Phase" switch to "Reverse" for both channels to sound correct with equal presence. What I'm wondering is if I hooked up that one speaker *exactly* as the book/screen diagram shows, with positive and negative opposite of general convention, if I could actually use the "Normal" position. Next time I'm out in the shop where the thing lives, I plan to give that a try.
     
  3. Ohighway

    Ohighway Wannabe Minimalist Subscriber

    I made that comment when it sounded like he was sold a 'working' amp that wasn't due to a missing , fairly expensive, rectifier tube. However I later surmised, the tube was missing because a solid state modification had been performed.

    Not sure why you're getting all jacked out of shape. :scratch2:
     
  4. RWood

    RWood The future is not what it used to be Subscriber

    Messages:
    1,454
    Location:
    Richmond, VA
    Yeah, you might be right. And mine might be wrong, lol.
    Fwiw, here is the diagram from the manual:
     

    Attached Files:

  5. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    OK guys, new rectifier tube ordered and a new matched quad set of output tubes ( JJ's) and some caps.

    Watch this space for when i need help re wiring the tube base after the knuckleheads work......
     
  6. Andyman

    Andyman Scroungus Stereophilus Subscriber

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    Because I think you were being petty. He got a helluva deal, The iron itself is worth more than what he paid, so everything else is a bonus, and worth a couple multiples of what he paid. To ask for an adjustment when you paid far less than an informed seller would ask I think is bogus.

    When one buys stuff used from private parties, it's caveat emptor; you pay your money and take your chances. The OP and his friend admit that they were ignorant of these things as they should have noticed an oddball tube and an open socket, or even asked to power it up. But they didn't and wound up getting a killer deal on a good amp regardless.

    I think my original post pretty much says it all...
     
  7. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    My friend would normally ask me before he bought something he wasn't sure of but he so wanted the amp that he rushed out and bought it without asking to see it with the top cover at least removed or see it working, the seller said he was inundated with emails, and at the price now we realize why.

    Anyway, as i said above the parts are on order and i will report back when they arrive for more help from you tube guys.

    Thanks in advance.

    Neil.
     
  8. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    She sings again...........

    And very nice she sounds..........

    [​IMG]

    [​IMG]

    I am one happy camper.

    :banana:
     
  9. gadget73

    gadget73 junk junkie Subscriber

    Messages:
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    Location:
    Southern NJ
    Be really careful about those JJ's. I hear a lot of things questioning their reliability. The EH tubes are supposed to be better in this regard. I have no experience with any JJ or the EH7591's so take that bit of hearsay for what you will.

    I'm not going to pretend to know anything specific about the Eico amps, but in some applications there are changes suggested to help make sure the tubes don't blow up. Fishers at least get the grid resistors and caps changed to different values. I don't know if that applies to the Eico but it might be worth looking in to.


    I do have to admit that I'm baffled as to why someone would re-wire the socket to stick a 6L6 in there paired against a 7591. Thats just....no. At least it was rewired though instead of just having a random different tube jammed in there. If it had not been, that would have done some really interesting and probably very bad things to the amp.
     
    Last edited: Dec 1, 2012
  10. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    Hi there thanks for the reply.

    I know little or nothing about tube amps as this is the first one i have tackled, the last time i used anything with a tubed amp section in was when i was a kid many years ago.

    Well JJ tubes were bought by my friend ( the rectifier tube is a Sovtek, i bet that one is no good as well eh ? ) and they are a matched quad set that are said to have been tested and matched, if we picked some sort of rubbish tubes then i am a bit disappointed, what can you do.....sigh.

    Anyway i have done my best and i will test her out for a few hours today and see how she gos, she sounded lovely last night, the amp was making my test bench Minimus 7's sing, and few amps can manage to drive those speakers that well.
     
  11. crispycircuit

    crispycircuit AK Subscriber Subscriber

    Messages:
    1,213
    Location:
    near Buffalo NY
    That's a great amp....

    They have excellent basic circuits that sound great. You'll have a hard time topping this amp. The coupling caps can make a big difference in sound so experiment with caps till you find what you like. Learn how to check the bias for each 7591 tube. Keep the 5AR4/GZ34 because it's a slow start tube and lets the filiment/heaters warm up before the high voltage/B+ is applied. Actually rewiring for 6L6s tube is fine and the Sovtek 7591s are 6L6s with a rewired base. The only problem would be the height of the tube and if you can get the cover to clear. Your amp is very clean and in great shape. The price was a DEAL! This amp will put older solid states to shame. You have a real gem and may not know it..... Cheers
     
  12. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    The amp just went back to its owner.

    I only had it here for repair, i had it on test for maybe 10 to 15 hours and it sounded great, my friend who owns it was very pleased with it.

    No more mods will be done, it will be in use in his system from tomorrow.

    I am just very pleased i could sort out the amp for him so it worked and sounded good.

    I can't say i wish to have another tube amp to fix anytime soon tho.

    I think i was lucky this time :)
     
  13. crispycircuit

    crispycircuit AK Subscriber Subscriber

    Messages:
    1,213
    Location:
    near Buffalo NY
    Your a good friend. Tube amps take special repair knowledge like any hobby. Get to know a tube repair man that will share his experience with you. Or just start reading tube forums and it will make sense.... Anyway, your friend should be very happy.....
     
  14. Cogsinister

    Cogsinister Super Member

    Messages:
    3,595
    Location:
    Atlantic Canada.
    No doubt about it, i learned a huge amount fixing up the Eico.

    My friend just informed me he has an old Heathkit tube amp in his storage locker that needs attention, here we go again.........

    :thmbsp:
     
  15. Lower Tones

    Lower Tones New Member

    Messages:
    13
    This is an old topic, but I think it important to state that, prior to sending this amp back to the friend, the push-pull pairs should have been biased, each channel. Not setting the bias means that the matched quad of tubes probably isn't any more. I'd bet that one tube per pair is suffering for it.
     
  16. Dandy

    Dandy Super Member

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    How would you bias the push pull pairs as this amp doesn't have fixed bias? Each channel is cathode biased.
     
  17. gadget73

    gadget73 junk junkie Subscriber

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    Near as I can tell you do not. The schematic indicates no adjustments of any sort. There are some cathode bias rigs with balance adjustments, but this doesn't appear to be one of them. Looks like all you'd have to do is check to see if its reasonable.
     
    Dandy likes this.
  18. drtool

    drtool It might get loud In Houston Subscriber

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    < Newest kid in class raises his hand.I have read that you can change resistors in a cathode bias amp to get closer to speck.?:dunno:
     
  19. gadget73

    gadget73 junk junkie Subscriber

    Messages:
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    you can if it needs to be changed, but in stock form there isn't any adjustment on this amplifier. Usually unless the factory bias point is just not useful or things have changed a lot because of higher voltages its not something you typically need to do though.
     
    Dandy likes this.
  20. archie2

    archie2 Addicted Member

    Messages:
    6,097
    Location:
    Almost Coastal RI
    I've had a solid state rectifier in my ST40 for years, works fine. There are a few tube amps that will take a SS rectifier and the ST40 is one of them.
     
    derekva likes this.

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