Eico HF-81 -- best output tubes?

Discussion in 'Eico Place' started by ssouci, Mar 20, 2017.

  1. ssouci

    ssouci Well-Known Member

    Messages:
    551
    Location:
    Vancouver, BC, CANADA
    I have a completely rebuilt Eico HF-81... virtually every part and wire has been replaced with careful choices by an experienced HF-81 rebuilder

    I've tried 3 sets of vintage NOS output tubes, with surprising results:

    #1. Siemens E84L / 7320 (heavy duty version of EL84 that can sub as a 7189)
    - sounded OK, but mid and highs lacked life and sparkle and sounded noticeably veiled)

    #2. Russian 6P14P-ER (heavy duty long-life version of 6P14P that can sub as a 7189)
    - sounded OK, but mid and highs lacked life and sparkle and sounded veiled)

    #3. Russian 6P14P ("plain" Russian tubes, inexpensive)
    - sounded very good all around, very good highs/mids, with maybe a tiny bit less strength in the bass vs. the others

    so I'm running the amp now with the plain cheapo Russians because they clearly sound the best, but I'm wondering why the two other tubes -- both of which should be "much better" tubes -- did not sound as good

    also, can anyone suggest the best output tubes to use specifically in an HF-81, where everything just clicks and they sound really great?

    hoping for a best-bang-for-the-buck option, and also an option that is simply the best (but might cost more)

    ideally, the options should reflect tubes that can be located and purchased within reason, and have a decent expected lifespan

    any advice or suggestions greatly appreciated, thank you!
     
  2. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,327
    That's surprising, I use 6P14P-ER's on mine and sound real nice in mine amp, do you have any pictures
    of your amp underneath?
     
  3. ssouci

    ssouci Well-Known Member

    Messages:
    551
    Location:
    Vancouver, BC, CANADA
    sure, attached here is a photo of the underside

    I should mention that this unit has been sitting unused for approx. 6 weeks, and I just recently powered it up... I could swear that prior to this, even the plain Russian output tubes were sounding a bit more lively with better high end... not sure if anything could have changed while the unit sat idle?

    the restoration is pretty recent, and there are fewer than 100 hours on this amp since that

    thanks
     

    Attached Files:

    drtool likes this.
  4. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,327
    That could be, everything has to charge up a bit, mine is a ongoing project I changed the coupling caps to pio's
    and the caps everywhere else to poly, I would give it time to settle in again and see. What kind of 12AX7's are you using
    and 12AU7's that makes a different's in the tone as well.
     
  5. ssouci

    ssouci Well-Known Member

    Messages:
    551
    Location:
    Vancouver, BC, CANADA
    my 12AX7 are Rogers (made in Holland)

    my 12AU7 are Mullard
     
  6. Mossback

    Mossback New Member

    Messages:
    31
    Location:
    The Great Pacific NW
    First of all having only 100 hours some caps may not have settled in yet.
    In order, vintage Mullard, reissue GL, USSR surplus OTK 6P14P-ER those in my experience are best sounding EL84's in the HF81. I have found it takes up to 100 or more hours for tubes to sound their best.
    The nine pin tubes you have are nice sounding.
     
  7. ssouci

    ssouci Well-Known Member

    Messages:
    551
    Location:
    Vancouver, BC, CANADA
    update:

    I have cleaned all the tubes pins with very fine sandpaper, brushed off with 99% alcohol, then applied a thin layer of Dexoit Gold (carefully to the pins only)... the pins were somewhat dark and discolored before, now are silver and shiny... the Russian output tubes were already shiny silver

    also, I discovered that one of the 12AU7s might not have been seated properly since it popped out along with the tube shield when I removed it (I had only partially inserted the 12AU7s because they were so hard to push in and I was afraid of breaking them... the tube sockets are new, and maybe the pins thicker than usual???... seems a bit easier to seat them now and I've been able to seat fully)

    after the above actions, she seems to sound a noticeably better overall, and I am now running the 6P14P-ER output tubes

    thanks everyone
     
  8. tube-a-lou

    tube-a-lou Super Member

    Messages:
    4,327
    I would not but anything in the tube sockets, Dexoit or anything that leaves any oil or substance like that.
    I had a guitar amp once and when I brought it home it sounded terrible, when I went inside to check the caps or
    resistor's someone but this green cleaner lube on all the tube sockets once I cleaned it with contact cleaner and
    a small dental brush it sounded so much better.
     

Share This Page