I hate my 5150!! (amp troubles)

[Fragle]

fuck that POS.

well, long story short, the mofo has been running dodgy for a few months now. when it works it sounds fine, unfortunately it doesn't work in a reliable fashion anymore.
i already had it checked out by an amp tech, but thanks to murphys law the damn thing worked perfectly fine when he checked it out, and he didn't find anything wrong with it.

here's the issue:
it'll work perfectly fine, and then all of a sudden the volume cuts VERY low, so low that you can turn the master to 5 and it's still at whispering volume. when that happens, the sound is pure fizz, no bottom at all.
when that error occurs, there will be a GIANT loud woooooosh coming out of the cab when flipping the standby on or off. sounds like you're on a shore, really.

i already tried the FX loop cleaning thing (contact cleaner on a guitar plug and rocking in and out a couple of times), no effect. patching the fx send to fx return also has no effect, so i guess the FX loop is out of the question.

any further ideas??? i could try a retube but the tubes aren't all that old really....besides, the amp was checked by a tech and he only replaced the V1 preamp valve due to noise issues but that's it as far as tubes are concerned....he even bias modded the thing and checked the power tubes, so i'm tempted to rule out the tubes, too.

i'm starting to thing that it might be the OT. but then again, why does it sometimes work just fine?

 

[John_C]

bad connection somewhere is my guess, you've got a lot of staring at solder joints to do!

 

[RevoltStudios]

Had this problem constantly with my old 5150. It's just a cold sauter joint or connection somewhere. Not really a big deal once you find it. These amps are popular around here for recording but the two I had out live were constantly breaking down. Cheap PCB amps

 

[Fragle]

i know jackshit about electronics. what kinda precautions do i have to take? maybe anyone got a pic that explains what i should be looking for?

thanks for the replies btw

 

[Lasse Lammert]

If you don't know much about electronics you should NOT OPEN THE AMP.
You wouldn't be able to find/fix a cold solder joint anyways (if that really is the problem), but you can really hurt or kill yourself (even with the powercord being unplugged!).

 

[RevoltStudios]

If you don't know much about electronics you should NOT OPEN THE AMP.
You wouldn't be able to find/fix a cold solder joint anyways (if that really is the problem), but you can really hurt or kill yourself (even with the powercord being unplugged!).

+1 Take it to a tech. If it is a cold joint it could only cost you $50 or so.

 

[Fragle]

ok, thanks for the warning.
having that said, i already took it to a tech, and he didn't find a problem! and i don't know any other techs in my area.....

hat jemand aus D zufällig ne gute adresse von nem techniker der sich mit 5150s auskennt parat??

edit: lasse, ich sag dir heut abend nochmal definitiv bescheid, sieht aber gut aus ;-)

 

[TheWinterSnow]

a little fun fact about 5150's...they where designed with bleed resistors. If you leave the amp plugged into the wall for about 30 seconds after you turn it off, all the filter caps drain, making the amp safe to work on. This isn't the same for every tube amp but most modern designs have this feature implemented. So yeah for the most part you can prob around in a 5150 without ever worrying about it.

Definitely sounds like to cold solder, and its probably in the preamp.

 

[John_C]

a little fun fact about 5150's...they where designed with bleed resistors. If you leave the amp plugged into the wall for about 30 seconds after you turn it off, all the filter caps drain, making the amp safe to work on. This isn't the same for every tube amp but most modern designs have this feature implemented. So yeah for the most part you can prob around in a 5150 without ever worrying about it.

Definitely sounds like to cold solder, and its probably in the preamp.

don't rely on bleed resistors to do their job seems to be a common idea in many books and articles on tube amps. If you don't a) own some sort of multimeter and b) are fully comfortable about what a capacitor does and why it might be be a bad idea to put your fingers in a device that contains really big ones without taking precautions then JUST DON'T!

 

[Wolfeman]

There was a thread about something similar last week, and I mentioned in there that my Hellfire did the same thing. Ended up being a crapped out phase inverter. So check that too. Cold solder joint or loose molex connector is also a good possibility. One thing is for sure, you know it's a power amp issue.

 

[TheWinterSnow]

don't rely on bleed resistors to do their job seems to be a common idea in many books and articles on tube amps. If you don't a) own some sort of multimeter and b) are fully comfortable about what a capacitor does and why it might be be a bad idea to put your fingers in a device that contains really big ones without taking precautions then JUST DON'T!

yeah for the most part, you need a multimeter to be sure that those bleed resistors haven't blown out. If they haven't burnt up then they work, meaning if you test the large voltage caps and get nothing, then they work. I know my 5150 works, but still I try not to touch anything connected to the hot side of a large cap.

but then again, if you don't know what a capacitor looks like or how to tell which components its connected to and not to touch it, you probably wouldn't know what you are looking for, so taking apart the amp will get you nowhere.

Its generally advices if you don't know at least the basics of electronics and troubleshooting circuits, you probably should't take a tube amp apart, because you won't fix whatever is wrong with it.

 

[Fragle]

just FYI, i sent it out to another amp tech and he said there are a lot of bad connections and cold solder joints - just like you guys pointed out. i'm having it repaired right now, and fortunately it's pretty cheap
pretty interesting though that the other tech i mentioned above didn't find those issues....
can't wait to get my beloved 5150 back on the road. i'm getting sick of the engl sound haha.

 

[if6was9]

just FYI, i sent it out to another amp tech and he said there are a lot of bad connections and cold solder joints - just like you guys pointed out. i'm having it repaired right now, and fortunately it's pretty cheap
pretty interesting though that the other tech i mentioned above didn't find those issues....
can't wait to get my beloved 5150 back on the road. i'm getting sick of the engl sound haha.

Not all techs are good. There's a guy in my city who gets alot of business but really isn't great. The venue I work in has sent him several things that he claims he can't find anything wrong with when there's clearly problems with the gear. Another tech has started doing stuff here more recently and has found tons of problems with the stuff the other guy has fixed. Apparently he's done wierd thing like bypass safety measures on some of his repairs and I know for sure he's replaced woofer and tweeter drivers with ones of much less power ratings without telling us, meaning they get blown again rather quickly.

 

[Fragle]

this is a neverending story.....

ok, in short words, i got it back from repair, plug it in, and it sounds like garbage. cold, buzzy, harsh, muddy. i've only played it at low volumes right now, gonna take it to rehearsal tomorrow and see how it behaves when cranked. on the other hand, before the repair it sounded decent even at low volumes (if it worked at all, of course)
i wonder if the guy fucked with the bias. it kinda sounds like it's ICE ICE cold right now, but it might as well be pretty hot therefore making it sound like shit at low volumes. (note: this amp has a bias pot installed).
oh, and the footswitch isn't working. now, i haven't used the one i got flying around here for AGES, so i don't know if it's broken or if the switching on the amp itself is broken. gonna check that tomorrow, too.

 

[Wolfeman]

Sounds like the bias is set too low.

 

[Fragle]

that's what i'm thinking too...but then again, why would he even want to re-bias the amp, and do a crappy job on top of that? makes no sense to me, so maybe he just did a crappy job at fixing the connections....

 

[Fragle]

ok, band rehearsal check done.
footswitch works fine, guess my other FS is broken
as for the sound, it's still a touch grainy but it really opens up with the post gain past 2.
is it possible that fixing any bad connections in the preamp messes with the low volume behaviour of the amp?

now, the thing is, i'm usually recording with the PG at 1,5 or something, which used to sound good but now is in the not-so-good zone...will be difficult to get the thing to sound good now, damn.

i'm actually considering to trade this for another amp. it's got to blend well with an engl fireball 100 (my main amp), both recorded and live (i'm running a stereo setup). the engl is really tight and clean, somewhat scooped midrange, so i need something fuller/nastier that gives a good midrange. two channels or more, better clean than 5150 prefered. fx loop necessary.
i'm a big fan of marshalls but that won't help me with my recording situation at all, hehe.
any ideas?

 

[Vinny]

Not what I wanted to see, since I plan on getting a used 5150 soon lol
This EXACT thing happened to my bud's Peavey ValveKing, but was fixed just by messing with the ohm selector (seriously).
No idea why really. But the amp tech just fiddled with the ohm selector (FYI it was on the right ohm selection when the problem started)
So maybe try that? (That is, if you're amp has multiple ohm selections, I dunno if 5150s do)

 

[TofNazareth]

I have two block letter 5150s and one just stared to have these same symptoms. Does any one know where the cold solder joints happen the most? Also any tube suggestions?

 

[decoy205]

I have a block letter too. Bought it used and it starting having this issue last year. I thought it might be the tubes so i changed them. it stopped for a while and then it did it 2 more times after that.

It sounds like the power section just stops working. All you hear is the preamp section. You just cant get any volume. The tubes all glow normally so its not the tubes. It must be either a bad connection or a bias issue. I guess this is pretty common. The amp sounds so damn good so I want to get it fixed. It don't really gig anymore so I just need it to sound good for recordings.