The Hughes & Kettner User Forum

The Unofficial guitar amp and cabinets forum for users of Hughes and Kettner products. We are not affiliated with Hughes and Kettner!!


    JJ el84s or Mullards?

    Share
    avatar
    glennsteen06

    Posts : 14
    Join date : 2016-03-07

    JJ el84s or Mullards?

    Post by glennsteen06 on Sun Mar 25, 2018 4:00 am

    I was thinking of upgrading my GM36, i think it sounds a little steril and to much treble, can't stand that treble sometimes Sad I thought maybe changing tubes might help a little and i was wondering if anyone have tried either JJ el84s or Mullards in it?
    Heard that JJs were a little brighter than Mullards. And then i heard the reissue version of the Mullards isn't as good as the original.

    Curious to hear if someone has tried swapping tubes to one of these brands Smile
    avatar
    bordonbert

    Posts : 1075
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: JJ el84s or Mullards?

    Post by bordonbert on Sun Mar 25, 2018 10:44 pm

    Have a look lower down at The Tube Swapping Thread just below this one.  In particular instead of reading through the whole lot make sure you look at Page5 from post #124 and look at what VoodooJeff has to say about valve swapping concerning his $120+ Wathen valve set.  (That's $120+ for a single 12AX7 not for a set!)  It's "subtle at best".

    You won't get a lot of tonal change with a valve swap between manufacturers, you never do.  The reports of "it gave me a new amp" are grossly exaggerated if people are honest.  Once you have invested in teh new valve set you are under real pressure to convince yourself you hear something which makes your money well spent!  We have all done it.  We buy something "knowing" it will be great and then - - - well - - - it 'aint so great after all.  Do we admit we have wasted our money, or worse, we have been hoodwinked by listening to others?  Not usually.  It takes a lot of honesty to admit we were just plain stupid.

    You will get much more obvious genuine change with speaker swaps and that should definitely be your starting point in sorting out the tone.  That fizziness in the top end is a very common characteristic of the amp and it is always improved more by changing to more suitable speakers than valves.  For my money it can be exaggerated by Vintage30s, some love it for that, and it can be reduced by G12M Greenbacks as I found, but I play only older classic 70s/early 80s rock so of course your tonal needs may be different to mine.  But I will say it can't really be removed no matter how old and "pure tone" your $50 NOS Mullards are.

    And my own recommendation as an engineer who knows what is going on inside each of the amp stages is steer clear of any 12A*7 type swaps even though "gurus" tell you they are amazing, they always screw up the designer's careful stage setup.  Those valves are NOT "equivalents", they are anything but.  They just happen to mostly be able to cope with the conditions a 12AX7 valve stage sets up without damaging themselves or other components around them, (usually but not always).  If you really must go down the path of "reduced gain", (there is no such thing in valve terms!), go for a 5751 which is very similar in characteristics to the 12AX7 but with an "amplification factor" or μ "mu" which is around 30% lower than a 12AX7, (remember that is NOT the "gain" of the valve, it is more complicated than that as it is tied in with two other parameters).  The gain in use is not necessarily the same as that amplification factor.  The stage design outside of the valve sets the gain and the amplification factor determines how closely that gain can be reached along with all of the valve's characteristics.  You can't change the gain of the stage with a 12A*7 swap without changing many other aspects of the stage behaviour, not all of them pleasant or reliable. Reducing the gain of a stage with a different valve type is a bit like making your car run slower by permanently levering on the handbrake a touch and putting in a bolt to prevent you engaging top gear. It works but it is so-o-o-o-o-o inefficient and unreliable.

    Anyway, enough preaching, I would suggest you have a scout through that thread and let us know what you think then maybe others will come in to make their suggestions.

      Current date/time is Sat Nov 17, 2018 1:57 am