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Troubleshooting my Imperial Lead Channel (tube?)

Discussion in 'Amp Central Station' started by adamajah, May 15, 2018.

  1. adamajah

    adamajah TDPRI Member

    95
    Nov 12, 2015
    out west
    I recently got a 20th Anniv. Tone King Imperial and love the heck out of it.

    The other night the Lead channel started cutting out when I had the Volume past 4 or so and laid into some loud chords. The Rhythm channel is fine - it's just when I switch to the Lead channel and strike a chord the volume drops dramatically all of the sudden.

    I'm guessing the problem is a bad preamp tube for the Lead channel, but could use some advice on where to start troubleshooting.

    I don't see any obvious red-plating, but I'm no expert.
     

  2. corliss1

    corliss1 Friend of Leo's

    Sep 13, 2008
    Lansing, MI
    Try swapping a preamp tube. It's the easiest thing to do. I don't have a schematic, and the only ones I found online were obviously copies and nothing official. You may want to email them and see if they'll send you one.

    If a tube swap doesn't do it, getting hit hard with a big chord could be a problem due to vibration, and you may need to take it to a tech.
     

  3. Dacious

    Dacious Poster Extraordinaire

    Mar 16, 2003
    Godzone
    Usually a preamp tube when one channel is good . V1 V2 both according to the manual (tubes to your left viewed from the front farthest from the power tubes) are the rythym and lead gain stages. That means either could have a bad triode but it may be V1b as that is used by lead channel only.

    One new $10 12AX7 could prove it out, then you just need one of whatever they use.

    That company has a good rep, the people who sold you the amp or them will make it good. I'd ring them, I'm sure they'd respond well.
     
    Wally likes this.

  4. adamajah

    adamajah TDPRI Member

    95
    Nov 12, 2015
    out west
    Thanks @corliss1 and @Dacious

    Yes, I've got a couple of good 12AX7's laying around so I'll try swapping them in one at a time.

    I have an email in to Tone King but no response yet and I'd like to use the amp for rehearsal tomorrow so I'm crossing my fingers this solves it.

    My band mate has an old beat up Imperial MKI that he's been gigging and rehearsing with for years and years with no problems and only just needed a couple new tubes recently. Amazing amps.
     

  5. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    One question.....do you have the attenuators assigned to function only on the Lead channel? If so, that is another source of suspicion. If you do not have the attenuators assigned that way and the tube subbing does not find a proble, it is tech time. I have only seen pictures of that circuit but would love to have one open to investigate. The MKII, which I have had open, is a great amp, imho.
     

  6. adamajah

    adamajah TDPRI Member

    95
    Nov 12, 2015
    out west
    No it doesn't seem to involve the attenuator but that was good thinking @Wally.

    Update: I jiggled some tubes around in their sockets, put the Imperial through some paces and the problem is gone. I'll see how it does tonight after a car ride and full rehearsal.

    Dang I love the way this amp sounds. I can't even decide which channel I prefer... they're both so tasty.
     
    Wally likes this.

  7. corliss1

    corliss1 Friend of Leo's

    Sep 13, 2008
    Lansing, MI
    If jiggling the sockets around fixed the issue I'd try pulling the tubes and reinserting them a few times. Might just be some crud built up on the pins that needs to get burnished off.
     

  8. adamajah

    adamajah TDPRI Member

    95
    Nov 12, 2015
    out west
    Thanks for the tip @corliss1 !
     
    corliss1 likes this.

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