Results 1 to 8 of 8

Thread: 6SJ7

  1. #1
    Junior Member
    Join Date
    Apr 2008
    Posts
    18

    6SJ7

    Has anyone any experience in employing a 6SJ7 [octal, sharp cutoff pentode] in a topology that would normally call for an EF86 (as in matchless)? I ask because I have several NOS RCAs [metal can]. One of those things that make you go HUMMMMM>

    Mikej

  2. #2
    Old Timer
    Join Date
    May 2006
    Location
    NYC
    Posts
    1,521
    The Gibson GA-20 uses 6SJ7's,but it will require an octal socket,the EF86 is a noval.The 6SJ7 has a much lower amplification factor than the EF86,meaning much lower gain.

  3. #3
    Senior Member
    Join Date
    Apr 2008
    Posts
    255
    It's a great sounding tube, but pentode design was still being developed at the time (read: they expected the tube to be in a heavy piece of furniture, not a guitar amp) and so they sometimes exhibit microphonics. If you can find a spring mounted octal socket or improvise one, that would be neato. They do have a really good sound, maybe a little less bright than an EF86 (high inter-electrode capacitance?) in somewhat similar circuits. Got plenty of gain in most circuits, unless you're trying to drive a power tube directly or something.

  4. #4
    Junior Member
    Join Date
    Apr 2008
    Posts
    18
    Thanks for the replies. I did find the schematic for the Gibson GA20 and that looks interesting. I have a good supply of NOS 6SL7 and 6SN7 as well so I think I'll work in that direction.
    Mikej

  5. #5
    Senior Member
    Join Date
    May 2006
    Location
    Cornelius, Oregon
    Posts
    1,155
    On those Gibsons, they mounted those pentodes in isolated sockets so they are generally not microphonic in those amps. Makes it hard to plug the tubes in but well advised.

    Greg

  6. #6
    Junior Member
    Join Date
    Apr 2008
    Posts
    18
    I was planning to build this a a "head" version. Do you think that would obviate the need to come up with some sort of isolated sockets to deal with potential microphonics?

    Mikej

  7. #7
    Senior Member
    Join Date
    Apr 2008
    Posts
    255
    It may alleviate that need when there isn't a pervasively high SPL going on around it. I figure some heads may as well be combos since they're either sitting on the speaker stack or in a room/stage/whatever with tons of watts getting pushed all around. For smaller jams or more limited environments I'm sure it'll be fine. My 6sj7 was a stand up radio, with the 6sj7 feeding a paraphrase (6sq7/6j5) preamp and PI with 6k6 outputs. Sounded damn nice until you hit an open D string (not E!) and the whole thing would start feeding back microphonically. You could start it by flicking the tube too. At least it was in tune I guess .

  8. #8
    Supporting Member
    Join Date
    May 2008
    Posts
    200

    try the GT

    Those come in Glass Tube version too. I built a head using the 6SJ7 preamp circuit of the Gibson GA50 since my 1948 model sounded so good. I've tried a half dozen metal and glass tubes in there with no trouble. I think they are less noisy than the EF86, and franky guys - the gain is quite hi. I annotated my schematic and forget exactly, but it had a bit more gain than a 12AX7. Don't take the data sheets as your Bible - who has EVER gotten 40 dB (100x) out of a 12AX7? No one - that's who!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. 6SJ7 gain set up?
    By casey73 in forum Mods & Tweeks
    Replies: 18
    Last Post: 01-31-2008, 05:39 AM
  2. 6SJ7 to 12AX7 ??
    By blodviol in forum Tubes (Valves)
    Replies: 10
    Last Post: 05-04-2007, 12:45 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •