Fisher 400 tube question

Discussion in 'Fisher' started by hlcass, Jan 8, 2018.

  1. hlcass

    hlcass New Member

    Messages:
    28
    I picked up my first tube stereo, a later serial numbered (78xxx) Fisher 400 in fantastic shape, with all original Fisher tubes. Not knowing the history of the unit, I briefly set it up with Heresy 1’s just to see if it worked as advertised. It sounded great, but it will head off to Casper at Stereo Rehab in Chicago for a complete going through.

    Might be a silly questions, but like I said, tubes are new to me:

    Is there any reason to save the original fisher tubes and use new aftermarket ones?

    Are tubes wear items and potentially having original more/less important sonically or for originality in your opinion?

    My experience is with restoring cars (American Muscle and British) where correct date or original parts can be a focus with a lot of folks.

    I am looking forward to listening to my restored Fisher 400!

    Thanks!
     
    Last edited: Jan 8, 2018

     

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  2. N9JCQ

    N9JCQ Active Member

    Messages:
    318
    Location:
    Buffalo Grove, IL
    Casper just did my ratty garage found 400 in November. You will not be disappointed. And Casper can and will give you the complete lowdown on tubes when you take your receiver to him. He will take the covers off and inspect it with you there and tell you what he is seeing. Its truly an amazing process. Ask him all about the tubes then, He is an expert with Fisher and Scott tube stuff.
     
  3. hlcass

    hlcass New Member

    Messages:
    28
    Thanks so much N9JCQ! Casper has done a fantastic job on my McIntosh stuff over the years. It is reassuring to hear he is just as good with Fisher tubes.
     
    N9JCQ likes this.
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,656
    Location:
    Glen Burnie Md.
    I would think on a later 400 the tubes may not be as used as on an Early model (low serial). If they test good and the sections pretty well match on the 12ax7's for gm, and the output's aren't worn to a frazzle, you have 2 choices. Use the original tubes, or pack them up and use old stock euro or domestic or new stock russian tubes. By the time yours came out FISHER was pretty much using Sylvania tubes vs. Telefunkens as the only tube units were the 400, 500c, 800c and 1 or 2 amps, maybe 1 or 2 tuners, and the 400cx2. DON'T use Russian Tubes in the Phase Inverter spots. There is a thread that addresses this with regard to a "noose" in the phase inverter circuit that won't allow Russian tubes to function correctly. http://audiokarma.org/forums/index.php?threads/fisher-400-service-bulletin.671281/ Ask your tech to read the thread and make the corrections to the circuit. There is also a thread on adjusting the Phase Inverter section without test gear that works fine . http://audiokarma.org/forums/index.php?threads/quick-and-easy-400-phase-inverter-adjust.559415/
    There is also a Glaring MISTAKE in the Alignment instructions for the 400 LATE MODEL (Serial >48001). http://audiokarma.org/forums/index.php?threads/400-eyetube-adjustment-procedure-wrong.687346/.

    Yes tubes are wear items like brake pads, and ignition points, but they generally last much longer. OUTPUT TUBES in Matched quads (original 7868's) are hard to find so an IBAM/IBBA circuit may be needed. http://audiokarma.org/forums/index....dividual-bias-adjustment-modification.601583/ I would recommend this even for the original tubes as their current draw at spec bias voltage may be all over the map, which contributes to increased distortion and unbalanced operation. 10ohm cathode resistors, 100ohm screen stability resistors, and a change o the grid return resistors to 220K, along with changing the coupling caps for the outputs to .068uf will increase longevity and safety in the outputs no matter whether old or new tubes.
     
    eduarsan1 and N9JCQ like this.
  5. hlcass

    hlcass New Member

    Messages:
    28
    Larry, Your responce was exactly what I was looking for and thank you for including information that I should know. You are a wealth of valuable information.
     
    Last edited: Jan 9, 2018

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