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Conference napalm::guitar

Title:GUITARnotes - Where Every Note has Emotion
Notice:Discussion of the finer stringed instruments
Moderator:KDX200::COOPER
Created:Thu Aug 14 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:3280
Total number of notes:61432

244.0. "Help! My amp is broken." by BCSE::DAUGHERTY (Mike Daugherty - MKO1-2/E25 - 264-0633) Fri May 15 1987 13:29

    My Fender Deluxe Reverb (ca 1963) is acting up terribly.  Light tapping
    on the cabinet or touching ANY of the tubes produces a terrible noise.  I
    don't really know how to describe the problem any better.  The amp
    received a full tube transplant a few months ago, so I doubt it's the 
    tubes - unless one has gone bad within a couple of months of casual use.
    
    I doubt that it's possible for anyone to suggest a solution based on the
    fuzzy description of the problem that I've given here.  What I'm really
    looking for is a "debugging" technique.  Are there any simple ways to 
    pinpoint the problem?  I'm not experienced at working on amps, so the 
    solution may be to take it to a repair shop.  Can anyone recommend a 
    repair shop in the Merrimack, NH area?

    Thanks,
    Mike
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244.1Sounds like the reverb may not be sufficiently isolatedDREGS::BLICKSTEINDaveFri May 15 1987 14:0913
    This sounds like a classic problem with spring reverb systems.
    It can happen if the reverb system isn't sufficiently acoustically
    isolated from the chasis.
    
    There a discussion of this problem going on in COMMUSIC (it's one
    of the more recent topics).
    
    According to that discussion (or my memory of it), turning off the
    reverb and still having the problem does NOT eliminate the possibility
    that it's a problem with the reverb.   You have to try to disconnect
    the reverb completely.

    	db
244.2warp factorRICKS::CALCAGNIFri May 15 1987 14:5910
    Dave's suggestion is a good one and I would certainly suspect the
    Reverb unit.  In case it is not however, another very common problem
    with Fender amps of this vintage is circuit board warpage.  The
    circuit boards in these amps are made from waxed cardboard and they
    tend to warp easily, causing breaks in electrical connections.  The
    debugging technique in this case is to open the amp and visually
    inspect for cracked or open connections.  Good luck.
    
    /rick
    
244.3SCOTT DUNHAM might be able to helpMILVAX::EATONFri May 15 1987 15:196
    I know of a guy that might be able to help you.  He works in Waltham
    MA at Centre Stage music (a store) but he also does things on the
    side.  He knows a lot about that kind of stuff and maybe he can
    help you.  His name is Scott Dunham, you might want to try to reach
    him through the store (call there to get his home #).  I think he'd
    be a good bet-at least to talk to about it.
244.4VIKING::BUSENBARKFri May 15 1987 17:0214
	Even though you have new tubes that doesn't neccesarily
mean they are not the problem. If you suspect the reverb unit
and turning it off doesn't solve the problem I would suggest trying
to find the tube(or maybe not the tube) by swapping one for one with
your old tubes. Looking at the back of the amp on the right side
the first 2 tubes(7025's) are for channel 1 and 2 preamps. As you move
to the left the tube before your power tubes(6v6's?or 6l6's) is a 12at7 
which is your phase inverter/driver tube. I had one go in my Showman
and actually would feedback without anything plugged in at all. It can't
hurt to try a few things if you have your old tubes or can borrow some.
	Is the terrible noise a hum or a whistle?
    				
    							Rick

244.5BCSE::DAUGHERTYMike Daugherty - MKO1-2/E25 - 264-0633Fri May 15 1987 17:064
    re .4
    
    The noise is difficult to describe, but it's more of a crackling,
    fuzzy hum than a whistle.
244.6unless you've modified it...LYMPH::LAMBERTThe only *real* BMWs are twins!Fri May 15 1987 17:2315
   My old Deluxe (non-reverb) started doing that at one time.  I took it
   into Daddy's in South Nashua (who in turn shipped it to their repair
   center in Salem, in case you like the "direct route") and they
   repaired/replaced a transformer.  Solved the problem nicely, and only
   cost about $30. 

   As for the acoustic isolation of the reverb, while I wouldn't rule out
   that as a possibility, I would think that if that were indeed the problem
   that you would have noticed it before.  The base note indicated that the
   current problem is new, whereas the isolation is something "designed in"
   to the amp, and unless you've moved things around, I can't see how it 
   would change.  (I'm assuming that by "acoustic isolation" db meant things
   like rubber mounting, etc.) 

   -- Sam
244.7how about?VIKING::BUSENBARKFri May 15 1987 17:286
    	When you replaced tubes did you replace a power supply rectifier
    tube? 5au4,5au7? I'm not sure if the Deluxe use's this tube and
    I don't have a schematic in front of me.
    
    							Rick
    
244.8ThanksBCSE::DAUGHERTYMike Daugherty - MKO1-2/E25 - 264-0633Fri May 15 1987 19:3916
    Thanks for all the ideas.  I'll try some of the ideas this weekend.

    re .1, .2, & .6                         
                                  
    I haven't modified the amp so I'm not sure how the acoustic isolation
    of the reverb would have changed recently.  

    re .7
    
    There are no 5au4 or 5au7 tubes in the amp unless there's another
    name for them.  The schematic lists GZ34, 6V6GT (2), 12AT7 (2),
    12AX7, and 7025 (3).
                                                
    
    Thanks again,
    Mike
244.9DREGS::BLICKSTEINDaveMon May 18 1987 15:3510
    re: .6, .8
    
    Err, let's just say that I wouldn't rule out the Reverb theory.
    
    It's quite common for spring type reverbs to develop isolation problems
    as the result of wear and travel.  

    	db
    
    P.S.  I speak from personal experience
244.10Status ReportBCSE::DAUGHERTYMike Daugherty - MKO1-2/E25 - 264-0633Mon May 18 1987 16:4011
    I tried a couple of the suggestions over the weekend.  I disconnected
    the reverb, but the problem still exists.  I then swapped tubes
    (one at a time) - no luck.  
    
    I didn't feel comfortable taking the amp apart to check for a warped
    board or other problems, so I bit the bullet and took it to Hampshire
    Music for repair.  I'll post their diagnosis when I hear from them.
    
    Thanks to everyone who provided suggestions.
    
    Mike
244.11Whoa !!! Wait a minute !!!ROCKET::ABATELLITue May 26 1987 16:1814
    WOAH !!!!! Back up, for a second anyway !! I used to rebuild those
    guys !!!  Turn the amp on about 2-4 on the volume. Just tap one
    tube at a time (gentle like !), the tube that makes the noise should
    be replaced. This is nothing more than a bad (microphonic tube).
    Either the 12ax7 or the 12at7 will probably be the bad guy. Maybe
    the pwr amp tube. I've replace tubes that were supposed to be good,
    but not meant for amp applications. TV's ok, no problem, but put
    them in an amp and they go to hell. Typical older fender problem.
    I really believe that you'll find a bad tube being the problem.
    I used to own a '64 deluxe reverb. It got ripped off and I wished
    I could fine one like it again. Oh well, maybe some year. 
    
    Good luck,
    Fred