Eico HF-22's total reassembly.

Discussion in 'Eico Place' started by marloubow, Nov 17, 2011.

  1. nerdorama

    nerdorama AK member Subscriber

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    Hi Martin,

    I've been watching your thread. Great job. You mention a mixed bag of tubes. I can recommend the Russian 6p3s-e tubes from Jim McShane as a good sounding option for the 6l6's and at a great price for a well matched quad.

    I like the way you painted the lamination edges of the power transformer to match the chassis as a contrast to the black end bells. I have a pair of Bell 2200b amps that are like this and I think it's a good touch.

    Again, nice job and Happy New Year.
    John
     
  2. marloubow

    marloubow Best Day Ever Subscriber

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    Thanks Guys!
    Now the fun really begins.:D

    I've taken voltage readings at most of the points specified on the sams schematics. They differ from amp to amp and I don't know how to interpret them.

    Is some of it the variations in tubes?

    Is some of it the changes in values in the MOD (see below)?

    Sams Schematic http://akdatabase.com/AKview/albums/...0Schematic.pdf

    The modifications;
    Quote:
    GordonW,
    I decided to go with your recommendations;
    C1a & b - (1)47uf / 450v
    C2a - 100uf / 450v
    C2b - 47uf / 450v
    C4 - 100uf / 100v
    R12 - 5.1K / 1 watt
    So with 30 min + at idle (source & speakers connected / no load), here are the numbers...I went thru them twice, just as a double check and they seemed to be holding within a few volts.

    Tube------Pin-----spec'ed--------Amp A-------Amp B------
    V1............1...........65V.................65V. ............71.5V
    EF86.........3............1.5V..............1.34V. ..........1.22V
    ...............6............60V...............51.0 V............66V

    V2............4............60V...............50.1V ............66V
    6SN7........5............320V.............325.8V.. .........313V
    ...............6............75V...............64V. ..............76V
    ...............1.............60V..............59.1 V............66V
    ...............2............320V.............341V. ............300V
    ...............3............75V...............64V. ..............76.2V

    V3...........3............425V..............407V.. ..........394V
    6L6GB......4.............430V.............410V.... ........398V
    ..............8..............35V..............35.4 V............35.4V

    V4...........3............425V..............401V.. ..........394V
    6L6GB......4.............430V.............407V.... ........398V
    ..............8..............35V..............35.5 V...........35.3V

    Tube descriptions...

    V1 / EF86 / amp A / International Servicemaster - Germany
    .................amp B / Eico - Mullard - England

    V2 / 6SN7GTB / amp A / Eico - 6SN7GBT- USA
    .................. / amp B / Eico - 6SN7GBT- USA

    V3 / 6L6GB / amp A / Eico - 6L6GB - USA
    ............... / amp B / Executone - 6L6GC - ?

    V4 / 6L6GB / amp A / Westinghouse - 6L6GC - Germany
    ................./ amp B / Westinghouse - 6L6GC - Germany

    V5 / 5U4GB / amp A / General Electric - 5U4GB - USA
    ................../ amp B / Westinghouse - 5U4GB - USA

    Like I said...a real mixed bag.

    All the tubes tested as "good" on my Superior Instruments TD-55 emissions tester, with the exception of both 5U4GB's which tested as "replace". They had about the same measurements on both tubes.

    (john...just saw your post...will look into it)

    That's the low-down.

    Any other places I need to get measurements from?

    So, where do I start to get these numbers moving in the right direction?

    Whew...!

    thanks

    martin
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone

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    Martin -- Overall, the numbers look very good, although the B+ from the power supply looks a little low. While it could be your rectifier tubes, it's more than likely due to your use of an inrush current limiter on the AC line. However, we really won't know anything until we know what the AC line voltage was at the time these readings were taken. When you get a chance, recheck your 6L6 readings again and note the AC line voltage across the primary of the power transformer, as well as that coming from the wall plug when the readings are take. Then we'll have a reference to judge the B+ voltages against. With that, we can determine if the lower B+ is due to the rectifier tubes, the inrush limiter, your AC line voltage conditions, or some combination of all these things. It would also be helpful to measure the AC heater voltage at the 6L6 tubes (pins# 2 & 7) at the same time as well. That will let us know if the overall voltage to the amplifier is within the range the primary of the power transformer was designed for. The effect of reduced voltage to the amplifier is to reduce the maximum power output available.

    Dave
     
  4. marloubow

    marloubow Best Day Ever Subscriber

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    Dave,

    Would that be across the 4 & 6 pins on V5 (5U4GB) looking for 375VAC?

    I would never have thought these numbers would be considered "overall, very good", considering how different they are from one amp to the other.:scratch2:
    But that's okay...I didn't know how to work the "resistors in parallel" formula until 2 days ago either...thanks for the math lesson, Dave. :thmbsp:

    What the scoop on biasing the tubes on these amps?

    thanks
    martin
     
  5. marloubow

    marloubow Best Day Ever Subscriber

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    Enid, Oklahoma
    Dandy,
    I actually looked high and low trying to find an illuminated rocker, toggle or button switch that I liked...still looking. The only other condition was it had to use the existing hole without any further enlarging.
    I am contemplating your idea as well...thanks.

    martin

    P.s.Dandy,
    Since you mentioned it and Dave, to his credit, is too modest...

    Quote:
    Dandy wrote..."Dave, I'd also like to thank you for the generous way you share your knowledge. If you ever decide to write up some online tutorials, I'll be in the queue to sign up".

    It took me forever to find it again.

    http://www.audiokarma.org/forums/att...6&d=1317298886


    Hope you don't mind Dave.
     
    Last edited: Jan 3, 2012
  6. MX117.MC7150

    MX117.MC7150 Listener Subscriber

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    Beautiful work. What are you asking for the pair? ;)
     
  7. dcgillespie

    dcgillespie Fisher SA-100 Clone

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    Martin -- Thanks for the kind words -- I always try to help where I can, as I know how I would have loved to have had a forum such as this back when I had so many questions of my own.

    The voltages to be rechecked in your amplifiers are the original voltage readings you took on V3 and V4 (the 6L6s) in the amplifiers. Additionally, at the time you check these, also check the voltages on the primary winding of the power transformer. These will be the two black leads that connect to the incoming AC power. If you will, measure directly across these two black leads, and then across the power coming directly from the AC power cord. These numbers will let us know what your AC line is running at, and how much drop is being created across the current limiter you installed.

    Also, check the AC voltage applied between pins# 2 & 7 of the 6L6 tube where the green wires are connected from the power transformer. This reading will tell us if the voltage supplied to the power transformer is within the range it was designed for.

    As to the voltages themselves, yes they are very good -- particularly on the small signal tubes (EF86 and 6SN7). It is quite common to have the voltages vary by 10% from the nominally specified voltages due to the values of individual components and variations within the vacuum tubes themselves. Also, some small signal pentode tubes like the EF86 can have even wider voltage variations and still work perfectly fine. If you look at the Sams schematic for your amplifiers, I'm sure you will find a note on it somewhere that indicates the deviation of voltages possible within "normal" operation, and the voltage supplied to the amplifier when the indicated voltage readings were taken.

    Dave
     
  8. marloubow

    marloubow Best Day Ever Subscriber

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    Location:
    Enid, Oklahoma
    Dave,

    I took these measurements with no significant idle time on the amps.
    Maybe 10 min. max

    New numbers...
    Amp A
    V3 pin 3 / 414
    .....pin 4 / 417
    .....pin 8 / 36.2

    V4 pin 3 / 410
    .....pin 4 / 415
    .....pin 8 / 36.2

    Amp B
    V3 pin 3 / 401
    .....pin 4 / 405
    .....pin 8 / 36.3

    V4 pin 3 / 400
    .....pin 4 / 405
    .....pin 8 / 36.3


    Amp A. Before current limiter / 118.8. After current limiter / 116.1

    Amp B. Before current limiter / 118.8. After current limiter / 116.2

    Amp A. AC across pins 2 & 7 - 6.28V

    Amp B. AC across pins 2 & 7 - 6.28V


    thanks

    martin
     
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone

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    Martin -- Again, the numbers look great! The 6.28 vac applied to the heaters is within .5% of the 6.30 vac ideal. That means that the ultimate AC power applied to the power transformer is almost dead on the money of the 117 vac design center it is specified to operate at. As for the output tubes, based on the current they are drawing and the voltage applied to them, they are each dissipating about 22 watts total (if they are a matched pair), which will allow them to produce low distortion with excellent life expectancy in this design.

    I have no doubt that the amplifiers are producing very good sound for you. You've worked very hard to bring these back from the edge. Enjoy!!

    Dave
     
  10. bhamham

    bhamham Super Member

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    Way to go, Martin!

    Great analysis, Dave. I learn something from just about every post you make - many thanks!
     
  11. marloubow

    marloubow Best Day Ever Subscriber

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    Thanks Bruce!
    Do you guys know of any way to tell the mfg'ing dates of the amps?
    All I have are the serial numbers. Amp A. SR# 4518 / B. SR# 4562
    thanks
    Martin
     
  12. marloubow

    marloubow Best Day Ever Subscriber

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    782
    Location:
    Enid, Oklahoma
    Just a quick update...

    I'm waiting on some 2 watt resistors (R10, 11 & 13) and safety caps.
    I'm in contact with Jim McShane regarding a matched quad of 6P3S-E's as replacements for the 6L6's (thanks John...AKA "nerdorama"). I have one 6L6 at present that is causing a bit of hum regardless of which socket or amp I put it in.

    Also, and here is where I'd like some input. The 5U4's test as "replace" on my emissions tester. They both test the same in "strength".

    Are these particular tubes known to test "low"?

    I can afford to replace another pair of tubes besides the four 6L6's. I just want to know if the 5U4's are where I should start.

    One other thing...
    A couple of days ago I had the amps on by themselves. The preamp was turned off...not intentionally, just an over-site. At the same time I had a power tool running and couldn't hear the loud hum coming from the right channel. Upon hearing the hum I noticed one of the output tubes (not the tube previously mentioned, but it's buddy) in the early stages of red plating.
    It hasn't happened since as long as I turn the pre on first.
    Is this common?

    At present I'm running the Eico's with a Yamaha C-70 pre and a pair of Klipsch KG2.2's and a powered sub. It's good, but still not the right match yet.

    thanks
    martin
     
    Last edited: Jan 10, 2012
  13. GordonW

    GordonW Speakerfixer Subscriber

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    The "tired" 5U4s could be why your B+ is just a tad low.

    However, since the amps match so closely, and the voltage is still within 10% of normal, I wouldn't sweat it. Use 'em... and if you can get some new 5U4s later, replace them whenever.

    To be clear- was the red-plating tube the mate of the one that caused the hum, in the same amp? If so, that may be related (grid leak, weaker tube than the other, or something similar). New output tubes should solve that- especially matched ones.

    Regards,
    gordon.
     
  14. marloubow

    marloubow Best Day Ever Subscriber

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    Gordon,

    Yes on all counts.

    martin
     
  15. Ohighway

    Ohighway Wannabe Minimalist Subscriber

  16. marloubow

    marloubow Best Day Ever Subscriber

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    Gentlemen,
    I’m ready to do some finalizing on my Eico’s.

    Replacing R10, 11 & 13 with 2 watt resistors and replacing C13 “death cap” with safety cap, .033uf / 250VAC / Y2 Film safety cap.

    I presently have the AC cord wired according to the assembly instructions. But, since I have a polarized power cord now, I’m not sure if I have it wired correctly for the safety cap to be effective.

    Could you guys check me?

    The neutral side of the AC cord is the foreground wire, it’s the closest to the camera (they are both marked).

    Thanks
    Martin

    P.s. Tubes from Mr. McShane are in the mail. :thmbsp:

    P.s.s. I know some of the bare wires look as though they are really close together, but, they're not. I just looks that way. I plan to insulate all the bare wire in this finalization.


    [​IMG]
     
  17. dcgillespie

    dcgillespie Fisher SA-100 Clone

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    Martin -- The neutral power lead should come in and connect directly to the two AC outlets, one side of the power transformer, and the safety cap -- the other side of the cap being grounded. The hot power lead should connect directly to the other side of the unswitched AC outlet, and the terminal on the preamp power socket designated for the power switch. The other power switch terminal on the preamp power socket should then connect directly to the other side of the switched AC outlet, and one terminal of the fuse post. The other fuse post terminal should connect to one side of the inrush current limiter, the other side of the limiter being connected to the remaining power transformer primary lead.

    Wired as such, neither of the AC outlets are fused, but both the power transformer and inrush limiter are. If the fuse should blow in this configuration, the amplifier will shut down, but the chassis will continue to maintain a neutral level for safety purposes because the fuse is positioned in series with the hot side of the AC power.

    Dave
     
  18. marloubow

    marloubow Best Day Ever Subscriber

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    Thanks Dave
    I thought it looked suspect.
    martin
     
  19. marloubow

    marloubow Best Day Ever Subscriber

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    Dave,
    Thank you...good directions.:thmbsp:

    This makes more sense.

    Will get to second amp tomorrow night.

    martin

    P.s. The "blob" on the safety caps ground lead bugs me too (heavy sigh).

    [​IMG]
     
  20. skypilot_one

    skypilot_one New Member

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    Very nice job! They really looked beat but now look like they are worth at least a grand!
     

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