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Blown Tube Replacement

  • 15-09-2007 7:12pm
    #1
    novarock
    Registered Users, Registered Users 2 Posts: 1,132 ✭✭✭


    One of the Tubes on my JCM 900 is not lighting up in the slightest, so i presume its blown, the amp has a tube failover so it still works, but im going to replace the tubes anyway. My question is if i buy 4 new 6l6 5881 tubes can i just pullout the old ones and put in the new ones without having to rebias the amp?


Comments

  • #2
    Voodu Child
    Closed Accounts Posts: 6,706 ✭✭✭Voodu Child


    Personally, I would re-bias the amp.

    If you're going to shell out a few quid on half decent valves (and i'd hope you are:D ), you may as well have them running properly.

    Buying a new matching set, even if it's the same brand, has no guarantee that the valves have the exact same operating specs. (Unless of course they are sold as such - ie Mesa/Boogie valves)


  • #3
    novarock
    Registered Users, Registered Users 2 Posts: 1,132 ✭✭✭novarock


    Damn it, i was hoping that i could do the work myself, I really dont have a notion on how to bias an amp, anyone care to
    a) recommend some decent tubes that wont entirely break the bank,
    b) explain or direct me somewhere that explains how exactly to bias an amp!

    Cheers!


  • #4
    mr_fruitbowl
    Registered Users, Registered Users 2 Posts: 95 ✭✭mr_fruitbowl


    http://www.eurotubes.com/euro-Marshall-DSLTSLV.htm


  • #5
    Eoin Madsen
    Registered Users, Registered Users 2 Posts: 2,117 ✭✭✭Eoin Madsen


    novarock wrote:
    One of the Tubes on my JCM 900 is not lighting up in the slightest, so i presume its blown, the amp has a tube failover so it still works, but im going to replace the tubes anyway. My question is if i buy 4 new 6l6 5881 tubes can i just pullout the old ones and put in the new ones without having to rebias the amp?

    If it's not lighting up then the filament is probably blown. I'd swap it around with another valve though, just to make sure it's not a break in the wire carrying the heater voltage to the valve socket.

    You could just drop in the new valves and hope for the best, but the bias will definitely not be the same as it was with respect to the new valves. Better at least do a check that it's not biased too hot, if not a full rebias.

    Don't run it too long without full valves, the imbalance puts the OT impedences off, and you could potentially damage it. I get valves from http://www.watfordvalves.co.uk.


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