Conference napalm::guitar

    	I have had similiar problems with tube amps,and unfortunately
    have learned to live with it. To speculate I would guess that your
    amp has an unregulated power supply which is drifting with the 
    AC line voltage in your house or you may find the power supply
    rectifier tube(5u4,Gz34/5ar4) has had a problem from the first
    day you bought the amp. I replaced my tube with a solid state
    equivalent and have seemed to sound more consistent. If line voltage
    is really the problem then a Variac may help your problem,but this
    is both costly and just one more thing to carry....
    
    
    							R
    

    I've experienced this also.  I thought maybe its humidity related,
    maybe it's due to hearing a certain tone on the car radio, house
    stereo, etc. that causes me to think my amp sounds different than the last
    time I played through it (human ear conditioning????)  I've even
    experienced this phenomena while playing through my Rockman.  One
    night everything sounds killer, the next (with no setting changes)
    sounds muddy (I have an AC adapter so it's not battery related).
    I have no answers for it.                   
    
    					Ron
    

    I've noticed this in my Boogie.  It varies from day to day.
    
    However, the problem seems to be reduced significantly with new
    power tubes (6L6's).
    
    You didn't mention how old your tubes are, but if they are much
    older than a year or two, you may want to replace them.  Tubes
    last me about a year, but I'm sure it's a function of how much
    you use the amp.  The more you use it, the more often you need
    to replace tubes.
    
    Tubes have lasted me much longer since I started practicing thru
    a transister amp.
    
    	db

    I thought I was the only one hearing (or not hearing) things.
    I think maybe the humidity has a lot to do with it.  After all a
    speaker's made of paper most times.   I play all solid state 
    stuff, so I can't blame it on the tubes.   I do notice a tremendous
    difference in my acoustic guitar when the weather gets muggy but
    I guess that's to be expected.   Maybe the actual wood in the electric
    gets flaky?  I wish I had more answers instead of more questions...
    
    	T.

     I'm believe the heat and humidity has everything to do with it!
    At Bob Nash's "SweatJam '88" I disconnected all my effects one
    by one, because nothing was working right! My chorus pedal didn't
    sound right, my limiter (which I always use) was killing my volume,
    even when I turned the limiter volume up. So I diconnected all the
    patch effects and ran the guitar straight through. I felt naked
    without the toys, but I had to do something. The next day at home
    in a "AC" room, everything worked great! Hmmmmmmmm, something went
    wrong somewhere! As far as changing tubes in a tube amp, I use that
    to an advantage. I have new (about 10 hrs old) tubes and I have
    old tubes (circa 1980). I here all this talk about changing tubes.
    A new tube will give you more voltage and clean up your sound, in
    my case I use 4 sylvania 6L6 tubes I got with my Peavey Mace amp
    in 1980. I look at it like buying "soft" Groove Tubes! When checking
    voltage on the amp itself, I find that the "old" tubes produce 78vdc
    at the given test points. The "newer" tubes produce 86vdc. The older
    tubes give me a smoother saturation. The clean channel isn't
    as clean as with the newer tubes, but I like the sound I get. Remember
    the old expression, "don't fix something that doesn't need fixing"?
    As far as my amp acting strange? I really haven't noticed any real
    change in any enviroment whether it be hot, cold, dry, or humid.
    I guess I got lucky. As far as my effects? That's a different story.
        
    Fred_who_hopes_his_"old"_tubes_keep_on_working_for_the_next_10_yrs!

    
    The Fender Twin I just bought started acting up on me. I had heard
    a few horror stories about them having reliability problems that
    required a lengthy trip to the service center. Mine was doing the
    runaway hum trick, and was sensitive to any kind of tapping on the
    front panel. One night I decided rather than bring it back to 
    EUW, I would try swapping power tubes since I had some 6l6GC's
    kicking around the house. I replaced all four power tubes with
    a set that has got to be at least 6 or 7 years old just to see
    if it would make a differance. As soon as I replaced the tubes
    the problem dissapeared. I can tap on the amp all I want and there
    is no more noise problem. I found the rear panel test points are
    real handy for setting the bias and balance. All you need is a 
    DMM to set them correctly.
    
    	I called EUW and told them about this problem. I asked them
    if I could get a couple of new tubes from them to replace the
    bad ones I pulled out. They said that while the amp carries a
    1 year warantee, the tubes are only waranteed for 90 days. If
    I want new tubes I have to buy them. Eventually, I will probably
    replace all the tubes with Groove tubes, or Mesa tubes, but I
    would've thought that EUW would take better care of me. Especially
    since I spared them from having to mess with it. 
    
    	I am not used to having to change tubes so often, but I guess
    a high-gain amp like this goes through tubes much faster than
    a clean sounding amp.
    
    	Live and Learn !!!
    
    	Mark Jacques
    
    
    

    re.7
    In the "old" days they called that "tube microphonics".
    Fenders have always had this problem. If you're not
    sure as to whether or not you have this problem, tap
    on your amps face plate at a lower volume, or tap "very gently"
    on your tubes one by one. If you hear anything out of the speaker
    change that tube. Altho sometimes it's just a dirty tube socket,
    I've found that changing the tube usually does it. It is also
    wise to balance the amp to the tubes. It saves things in the long
    run.
        
    BTW....leave the guitar disconnected when checking this.
    
    Good Luck,                
    Fred

    RE. .7 Your absolutely right, tube microphonic problem. Trouble
    is, that the amp would go into major hum mode regardless which
    tube you tapped on, or if you tapped on the front panel. First
    I replaced 1 pair, and the problem seemed to go away, for a while.
    Soon after, it started doing it again, so I changed the other pair.
    The amp no longer suffers from this problem (knock on wood), although
    I haven't used it at real loud volumes yet.
    
    One problem I have with correlating home practicing to live situations
    is that in a live situation the amp is usually pushed back further
    and cranked. At home it is closer in front of me and used at lower
    volume levels so it is hard to predict what will happen when you
    get on stage and start whalin on it. An example of this is the
    problem I had (or Tom D. had) with my Telecaster treble pickup
    at Sweatjam. At home listening levels the problem was tolerable,
    in fact I can get a great controllable feedback with it through
    my Pignose or my Twins, but outdoors through a cranked amp, it had
    a severe microphonic problem. I am in the process of improving the
    grounding on this guitar. If that doesn't work, I will have to
    start looking into differant pickups, at least for the lead position.
    I am currently using Duncan Quarter pounders. It is also possible
    that the lead pickup is not properly potted. If this is the case,
    Seymour Duncan has agreed to repair/replace it.
     
    In the immortal words of David Bromberg (who probably stole this
    line from some other immortal sole) 
    
    	"You have to SUFFER, if you want to sing The Blues"                                 
    
   	(This person obvious has experience with tube amps) 
                                                  
    Mark
    

    1. 	Speakers will change tone greatly with humidity and age. This
       	may be why the change of some bassists to the Guild/Hartke (sp)
       	aluminum cone speakers. Jerry Garcia commented on this in last
       	month's Guitar Player.
    2. 	Cables can cause loss of high end because of capacitance of the
       	cable itself. This factor does not usually change much over
    	time. A bad cable (or cheap one) will not improve, so a little
    	extra money on a cable is worth it (ie Whirlwind etc)
    3.	Tubes can cuase a lot of funnies, but in general if you are
    	using the amp a lot change the power tubes, or a least get them
    	tested once a year. The preamp tubes are usually good for two
    	three years but should be tested with the others. DON'T move
    	the amp while the tubes are hot, the internal compents a can
    	come loose and cause microphonics. 
    4.	Humidity itself can cause high power connections to become corroded
    	and bring unpredictable problems. Cleaning these connections
    	(ie reseating the tubes) can correct this.
    
    Hope this helps
    Fred

    see note 396.18 : the Groove Tube book has a troubleshooting section
    
    Paul

    Okay, after four or five notes referring to your original note (396.18)
    we got the picture...   ;)
    
    jc (wearing his moderator hat)