Amp probs...

Discussion in 'Amps and Cabs [BG]' started by bassist4ever, Mar 19, 2003.

  1. I just turned my amp on to play some tunes and the thing crackles when i hit a note but it stops...kind of like its not warmed up or something.. its an Ampeg B 115 of the 70's years.. the owner (whom i'm borrowing it from) said to check something in the back if it ever started acting up... and i dont know what it is?
  2. okay how is this description

    on the attack of the note it "crackles" but then it sorts itself out and plays the note correctly till the next note.....

    c'mon people someone has to know something!:bawl:
  3. I have actually had the same problem with my peavey, I know exactly what you're talking about. I'd like some help also
  4. I have the same problem with my Peavey TNT bw-115. Except, mine crackles/is staticy and cuts out sometimes.
  5. ahh the owner of the amp told me to take out something in the back that plugs in and then has screw retainers. and have them tested @ the local music store. well they are bad so i have to have new ones

    numbers on it are 2N4348 RCA 7545
  6. Output transistors. I wouldn't bother testing them at the store. Just order a complete set of them from Parts Express or Mouser and be done with it. Order them by the number 2N4348 or NTE284.

    They're $10.43 each from either place.

    Notice the mica insulating washer and the litlle plastic insulating pieces when you pull the old ones off, be sure to put the new ones on the same way.

    And DON'T remove the grease, it's there for thermal conductivity.

    The Peavey output transistors are probably stamped with a Peavey "house number". But if you dig around in the technical section of the Peavey web site you'll find a tech note that will cross reference the Peavey number to a common number (my old Peavey crossed to a 2N3772).

    Good luck.
  7. Shop Time!

    Have good tech completely go through it and have her "fine tuned" top to bottom.

    It's worth paying a qualified tech, 'cause if anything goes wrong... it's their fault.
  8. 10 bux each.. and i need 4.
    found a guy in joplin!~
    goin to get them today
  9. well on eproblem..... i dont have the money to have a tech tear into it and fix it...if i trouble shoot it myself i can keep some of the cost down...
  10. I hope you know what you're doing, or else when you put the new transistors in they could just fry in a puff of smoke. That's what happened to me when I was starting out.

  11. is there a certain way to put in 4 transistors? he put some kind of rubber stuff with an adhesive on the transitor side...
  12. Are all (4) the same part number? Usually, but not always, they come in complementary pairs. Check the originals to make sure you didn't need (2) of one kind and (2) of another. If so, you'll need to be sure and put the right part number in the right place. If they are all (4) the same, then you just plug them into the (4) spaces.

    Note that the two transistor legs are closer to one end of the transistor than the other and rotate it so it lines up correctly with the holes on the amp.

    Leave the heat grease on there. It helps transfer heat from transistor to chassis/heat sink. Also, that crap gets on everything if you're not careful!

  13. so i did put them in right they guy put some kind of thing on the transistor so that i don thave to put grease on it. its like a rubber type thing with an adhesive on th etransistor side...
  14. :bawl:

    okay i got them put in
    but now all i get is a hum
    and the cone is pushed a good ways out

    what could be wrong?

    edit : i just looked at the transistors and they have this label

    h 8419
  15. my catalog cross references these to a NTE 284, if they sold you 274's you could be royally screwed. Hope no smoke came out.

    (ya shoulda mail ordered them from Mouser...)

    If this is an ancient amp, there weren't complementary pairs developed yet, so all 4 would've been the same.

    I'll try to look up what the 274 is, maybe it's a PNP version of the 284.
  16. this amp is from the 70's back when solid stat was first comming to be popular i believe (i'm no amphistorian).

    The guy said that they should work because they are "bigger" electronically. Naturally i have no clue in this area of electronics all i know is plug it in viola! power!

    No smoke came out. So if these arent right i'm going to order them from that mouser place seeing as how i couldn't find anything on the other page.
  17. "bigger" electronically???? Whoever said that is BS'ing you. You can't just substitute one transistor type for another because it's somehow "bigger". It appears the 274 is a Darlington high-gain transistor, though I don't have a spec sheet handy.

    I just hope you haven't fried anything else, otherwise you could be throwing good money after bad. There's several other transistors that "drive" these output transistors. Before you buy new transistors, put the old ones back in and see if the amp works as it did before. If it appears to work fine, get the proper transistors from Mouser and put them in and you'll be done. If it doesn't work, check all of the connections. You may have to take the amp apart a little to check the back side of the transistor mounting bases; make sure everything is connected. The mounting screw on one side actually must connect to a wire (this wire goes to the "collector" part of a transistor).

    When you get a chance, take a beginning course in electronics at the local community college or vo-tech. This knowledge will give you dividends the rest of your musical career.

    Good luck!!
  18. so that transistor isn't the right one?

    okay... i put the old transistors back in.... plus the new "micas" that he sold me...(least they work :mad: )... and its working good as new!
    the crackle isnt even in there any more.