• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Amp repair help!

Luke19Boarder

Luke19Boarder

Jul 5, 2001
1,524
2,083
Chicago, IL
lwke.bandcamp.com
#1
So I've got a Peavey Pro Bass 500 (Link Removed)

And it's been giving me 2 problems.

1. Sounds distorted at low levels. When I turn it up a bit, it's clearer (40-60% up it's a good, clean sound). Checked cabs, cables, instruments, you name it ... it's the head. I'm thinking maybe blown pre-amp tube, but I don't know for sure.

2. Output cuts out after using it for extended periods of time (25-60 minutes). I'm guessing that it's overheating, though I don't know for sure.

Would either of these be an easy fix?

I'm trying to avoid taking it in, because they charge 60$ just to open it up, and then hourly/parts beyond that at the local music store.

I'm just looking to fix it up so I can put it on the market, I've got a better one on the way :)
 
#6
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hi! I'm your friendly amp technician! I live perhaps thousands of miles outside the range of hearing and seeing your amp - even when it's turned up and working! So I've devised this handy questionnaire! In order to help me more efficiently diagnose and repair the problem with your amplifier please respond to the following points:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1. Describe your problem:

2. Now, describe your problem accurately:

3. Speculate wildly based on faulty knowledge about almost everything
just what's the cause of your problem:

4. Please indicate the severity of your problem:
A. Minor___ B. Trivial___ C. Minor___ D minor, the saddest of all keys___

5. Nature of problem:
A. Sounds bad___ B. Sounds really bad___ C. No sound___
D. Strange smell___ E. Smells really bad twice___

6. Was your amp plugged in?
Yes___ No___

7. Was it turned on?
Yes___ No___

8. Did you try to fix it yourself?
Yes___ No___

9. If so, did you make it worse?
Yes___ Yes___

10. Did you have a "friend" who "knows all about amps" try to fix it
for you?
Yes___ No___

11. If so, did they make it worse?
Yes___

12. Have you read your manual?
No___ No___

13. Do you have the manual?
Maybe___ No___

14. Are you absolutely SURE you read the manual?
I was going to___ No___

15. If you think you read the manual, do you think you UNDERSTOOD it?
Yes___ No___

16. If YES, explain why you can't fix the problem yourself:

17. What were you DOING TO your amplifier at the time the problem occurred?

18. If you answered "nothing", explain why you think there's a problem:

19. Do you have another amp you can use while you wait to take this one
to a repair shop like you should have done in the first place?
Yes___ No, I prefer to be out of commission longer___

20. Are you sure you're not imagining the problem?
Yes___ No___

21. Does the clock on your DVD player always blink 12:00?
Yes___ That's a clock?___

22. Do you have an independent witness to the problem? (Does not
include drummers)
Yes___ No___

23. Have you given the amplifier a good whack on top?
Yes___ No___

24. Did the amplifier catch fire?
Yes___ Not yet___

25. Has the foam or insulation inside your speaker enclosure
ever caught fire?
Yes___ No___ Huh?___

26. Did the insulationy stuff inside your speaker BOX catch fire?
Yes___ No___

27. If so, did you replace it with an approved dampener?
Yes___
No, enough beer gets spilled in there to keep it safe___
No, the cat whizzes in there after a good scratch on the
carpet anyway___
 
#9
A defective preamp tubes symptoms could range anywere from just slightly not sounding quite as good as before to a very distorted sound to completely not working at all. I've seen preamp tubes that malfunction intermittently sounding fine for awhile and then suddenly distorting again. Swapping preamp tubes is a pretty easy inexpensive thing that lots of amp owners successfully do.

note: Even after an amp has been unplugged for awhile, someone could still be shocked touching certain things inside. However handling the upper glass portion of a tube can be done. They just firmly pull out, you line up the gaps between your replacements pins and the matching socket and very carefully push it in.

But before you try that, another fairly common problem you might have is dirty switching contacts in the effects loop return jack. A real easy test you could try the next time its malfunctioning is to simply plug a regular guitar cord between the send and return jacks of your amps fx loop. (if your amp doesn't call these an effects loop but has 2 jacks that are labeled preamp-out and poweramp-in, connect these 2 jacks together with your cord instead) If this immediately corrects your problem, you could simply leave a short cord in place permanently or use Deoxit brand electrical cleaner to hopefully get it all cleared out and working right. Sometimes just repeatedly inserting a plug in and out of the return (or power amp in) jack will corect this situation too.

Good luck !
 
#10
Well, after (carefully, obviously) opening up the amp, I've got good and bad news.

The good news: The fan wasn't connected, and thus not working. I fixed that, so one problem is fixed.

The bad news: I replaced the tube, but it still sounds distorted. I also tried fiddling with the send/return jacks as you suggested, anderbass.

The sounds is distorted whenever the "signal" light turns on. I can try to get an audio recording of it and post it if anyone thinks that'll help?
 
#11
I see you're in Michigan. The best guy in this part of the world is Morrell electronics in Farmington. Most all tech shops have bench charges. They are usually applied to the price of the repair. That's just the way they do business(they charge for their time.) Too bad yer unit is broken, but, most likely reparable(not an amateur-type job). If you're not interested in repairing it, how much would you consider selling it for?

Josh
 
#12
While you have it apart spray some tuner cleaner in your Pots.
You may want pull each tube out and then put it back in the socket about 20 times. This will scrape off any oxidation in the socket and on the tube pins that may be keeping you from having a good contact. This message will self distruct if you read it.
 

Latest posts

Top Bottom
Back