Conference napalm::guitar

	Trouble shooting an amp over the net is always a challenge. A
"distorted buzz" really could be a variety of thing's. But first don't
waste your time with finding a tube tester at a Supermarket or Drug
store. Those testers test at a much lower voltage(almost half) of what
your amp see's. Unless the tube is dead,real dead it won't give you much
information. First try using the Princeton with a separate speaker to
see if the buzz is from power tube vibration. Another way is to tap each
tube lightly and listen for noise as you tap it.
	Fender amp's have clamps which hold power tubes in the sockets and
spring loaded covers which keep the preamp tubes in there sockets. I
would suggest pulling the power tubes(6v6's)and bending the holder's together
as tube vibration is a inherent problem with Fenders. While you have the 
power tubes out look at the pins and the bakelite? case and clean or blow
off and dust,dirt on the bakelite. If the pins are corroded or dirty try
cleaning them. If any oxidation has built up clean it off the pins. I've
heard of people using certain comercially available substances to clean
the tube sockets/tube pin's but have never used any myself. Pull the preamp
tubes(7025/12ax7) and reinsert them. 	
	The last tube is a 5u4gb rectifier tube which usually would put out
a constant noise if bad or going. It also has a tube clamp which can be tight-
ened and the tube checked out for dirt etc. If none of this work's then
it would help to get more description of the buzz. How old are the tubes?


							Good Luck,

								Rick
 

    Some Radio shcks have a tube tester. I know the one in westboro
    has one.
    

    An updated status on the problem:  Rick, I took your advice on looking
    at the tubes for loose connections/corrosion.  In typical
    "cart-before-the-horse" fashion (for me anyway), I have to wait
    another month or so to pick up an electric guitar to test this out.
    That was sort of my arrangement with my friend: fix the amp and
    you can have it for a while to start your set-up.
    	So anyway, the results of my poking around:  There didn't seem
    to be any loose connections or corroded parts, although the biggest
    tube (power amp tube?) is a little loose if you shake it back and
    forth.  I may still try a tube tester somewhere, just because it
    LOOKS like one of the little leads internal to one of the preamp
    tubes may be gone.  It's tough to tell though, but perhaps worth
    a shot.  While a loose corroded part could be the problem, it seems
    funny that the amp worked fine before my friend started imitating
    Jimi Hendrix, and the amp now sounds bad after two days of his assault
    on his listeners' ears.
    	As for a further description of the distortion,  there is no
    noticeable (read: glaring) distortion in the quiescent mode.  When
    you play a note/chord, the distortion is something like a low, flat
    (in tone) rumbling which tails off with the note.  I don't know
    if that answers the question about the "buzz" or not.  The tubes
    look as if they are as old as the amp...I'd be surprised if they
    had been replaced before.  A last question:  what is the cost of
    replacing these tubes?  Is it a lot?  Let me know if I (most likely)
    need to provide more detail about the situation.
    
    Dave

    I keep going to Radio Shack, but the 6l6 or big tubs are about $12.00
    and the others 12x?? are about $6 or $7. I replaced all the tubes
    on my Band master about 6 month ago and it cots me about $45 or
    $50. I really do not remember.
    
    By the way, I had the power tubes (6l6) priced at a tv repair shope.
    Because you get a brand name like GE, they wanted $45 a tube. It
    would of cost me more to replace the tubes than what I paid for
    the amp.
    

    
    I would recommend avoiding Radio Shack tubes, which tend to be
    microphonic (i.e. they can cause noises relative to vibration of
    the tube) and don't go a TV shop either, they will be overpriced
    (as noted in .4).
    
    Go to a music store and buy Groove Tubes or go to an electronics
    wholesaler and buy Sylvanias if you can get them.
    
    Groove Tubes are specifically tested to be OK for musical instrument
    amp use (i.e. low microphonics, low noise).  Mesa Engineering (the
    folks whio build the Boogie amps) sell their tubes by mail order,
    as well, but they tend to be more expensive.  Also these brands sell
    matched pairs of power tubes which will give a cleaner sound to
    the power amp stage.
                                                  
    

        A couple  of  ideas  that  may  help  - it still could be the
        speaker at fault,  and  from  your  description of the events
        leading to the damage, I'd look more closely at it.
        
        I know it was  checked out on your hi-fi, but there are a few
        particular electronic limitations on judging the speaker good
        by this method.  Most hi-fi  systems will deliver their rated
        power into 8 ohms (marked on the  speaker  magnet  usually) -
        many  instrument  amps  have  speakers with impedances higher
        than this, eg, 16 ohms, hence the hi-fi is  not  powering the
        speaker hard enough to demonstrate the buzz, or it may not be
        delivering a  high enough dynamic range of sounds, especially
        at the bass  end  to  drive the cone of the speaker into it's
        distortion area.
        
        It still could be  the  tubes,  but  it  smells  of a damaged
        speaker cone to me -  even  Hendrix  at  full power shouldn't
        damage tubes, but speakers are (comparatively) easy to break.
        
        FWIW
        Andy
        

	Tube testers will not apply the voltage(400v+/-10%) that your amplifier
will see at any of it's tubes. It is common to see a 150-200v from these type
of testers. Some do have a short light indicator,and if the bulb isn't burned
out,is helpful for a certain "no sound" situation's. As far as buying tubes
I have found the "Groove Tube's" to be the best buy as their matched pairs call-
ed Duet's(2) or Quartets(4) are really good high performance tubes and seem to
last compared to off the shelf stuff you get at an electronics supply.Seymour 
Duncan Convertibles come with GT's as stock. 
	Radio Shack tubes are low quality and cheap and are unmatched! Tv/radio
shops charge twice what most electronic's store's as they get there stock from
Gerber,Newark Etc. 
	Groove Tubes are actually tested in amplifiers before they are sent out
and are matched output characteristics. They are sold in pairs and fours.
	Mesa matches there tube's differently by specification's rather than
actual use.
	Groove tube's are more expensive but my rational behind buying them
is the way they are matched. If I compare it to buying tires it's similiar to
buying two different brands of steel belt radials. The wear on each tire will
not be the same from manufacturer to manufacturer.Since this can have an 
adverse effect on other components in the amp the extra expense for the tube's
is worth it. (Ever see a Marshall go up in smoke?)
	Did you try another speaker with the amp? It really sounds like
    power tube rattle.	 

    
    	Sounds symptomatic of a blown spkr to me...you'll need to connect
    the amp to a different spkr in order to troubleshoot -
    
    	JJJ
    

    	This amp is the only one I have to experiment with.  I don't
    have another speaker with the correct plug to try out the blown
    speaker theory.  I work in LTN and live in Watertown.  Would anyone
    near either area be willing to help me out with this problem?  It
    would be much appreciated.  Thanks,	
    					Dave

    Even if you don't have another speaker with the correct plug, you
    can test the blown speaker theory with a couple pieces of wire the
    same gauge as used in the blown cabinet. Simply pull the leads off
    the suspect speaker, connect the extension wires to them and connect
    the remaining free end of the extensions to the known good speaker.
    
    Yeah, yeah, Mickey Mouse, but it'll work good enough to settle your
    "Is it the speaker?" issue...
    
    Edd