5150 Help

[Genius Gone Insane]

I've had my 5150 head for 10 years and something is wrong with it. Hopefully you can help.

Recently it started dying I think. The high end is ok but there's this nasty sound coming out of the low end. It's pretty jacked and sounds something like what a blown woofer sounds like. Before I take it to a dealer I'd like to get some input from you guys.

The problem is definitely the head. I've tried different cabs, different speaker cables in each output, different guitars, ground switch, etc.

Maybe a year ago I got new tubes on it to replace the stock ones. I put the old tubes in last night but that made no difference.

S.O.S!!!

 

[006]

Maybe you fried something on the board? I'm not a technically savvy person when it comes to amp problems, then again, I've never had any problems with any of my amps either, so I've had no chance to learn anything. Heh. I'm just guessing it's something fried on the board.

~006

 

[cobrahead1030]

i know this sounds really out there, but it could be due to your input jacks (probably for the fx loop) being dirty...i can't tell you the specific reason as i'm not an amp tech by any means, but dirty input jacks can cause those amps to do some crazy stuff

go to www.fjamods.com and e mail the guy there, with the info you just posted here...he may be able to help you sort it out

 

[JeffTD]

Yeah, Jerry's the shit. Do you notice any volume loss or headroom defiency? 90% of the time, a problem with a tube amp is the tubes themselves.

 

[Genius Gone Insane]

Yeah, Jerry's the shit. Do you notice any volume loss or headroom defiency? 90% of the time, a problem with a tube amp is the tubes themselves.

No noticeable volume loss and I don't think it's the tubes. The tubes are hardly used. I haven't played much out of that amp this past year.

 

[Genius Gone Insane]

FYI Jerry's response:

"Hi,
Did you swap the preamp and power amp tubes? My first guess would be a
tube problem of some sort. The 5150's have a problem sometimes where the
effects loop jacks get dirty and cause some strange problems. It happens
most often to guys that don't use the effects loop. You can rule that
out by switching the loop off with the footswitch or plugging a jumper
cord in the loop. Plugging a cord in and out of the loop a few times can
clean them up sometimes. The best way to clean them is with a quick shot
of contact cleaner and then plug a cord in and out a few times.
Try plugging your guitar straight into the effects loop return jack and
see how that sounds. Is it a nice loud clean sound?
Jerry Pinnelli
FJA Mods <http://www.fjamods.com>; "

 

[Genius Gone Insane]

I'm going to bump this one up.

I took the head in to a dealer in Concord where the guy took a listen to it. It sounded great coming out of a Behringer cab (??????). The dealer said he was familiar with 5150s and that this one sounded great despite being so old.

So I tried again at the studio, double checking everything (cords, guitars, cabs, even power outlets), and I still had the problem. However, I figured something out: The sound starts getting fucked up when I set the pre gain between 5 and 6 and above. Below 5 sounds good, and now that I think about it the dealer might not have checked the pre gain being that high.

Anyone else have any ideas? This is killing me!

 

[Wolfeman]

Wouldnt that be a tube problem then??????

 

[Mr. Brokenamp]

I would still swap in some different 12ax7's.
Can you post a clip of the awful sound? That would give me a better idea what it could be.

 

[Genius Gone Insane]

I would still swap in some different 12ax7's.
Can you post a clip of the awful sound? That would give me a better idea what it could be.

OK thanks, I will...gimme a couple days though.

 

[JeffTD]

Could be your cabinet farting out, or the tubes overworking to produce that much gain.

I found my old 5150 pretty unuseable with the gain up to 6, but I always ran it at 4 with an OD infront.

 

[Genius Gone Insane]

Could be your cabinet farting out, or the tubes overworking to produce that much gain.

I found my old 5150 pretty unuseable with the gain up to 6, but I always ran it at 4 with an OD infront.

Definitely not the cabinet.

 

[Mr. Brokenamp]

It's hard to say without looking at it and hearing it. From the description it sounds (no pun intended) like one of the stages is getting overdriven too much.
Look for charred components. Don't poke anything in there unless it's nonconductive like a yellow pencil or piece of plastic and never ever touch the big capacitors or you might need to go to a hair stylist:~)

 

[Genius Gone Insane]

It's hard to say without looking at it and hearing it. From the description it sounds (no pun intended) like one of the stages is getting overdriven too much.
Look for charred components. Don't poke anything in there unless it's nonconductive like a yellow pencil or piece of plastic and never ever touch the big capacitors or you might need to go to a hair stylist:~)

Can you go into a little more detail here? When you say charred, do you mean darkened or dirty or what? If I do find anything, what should I clean it with? Thanks...

 

[Mr. Brokenamp]

Sorry I wasn't clear, charred as in burn marks. Burnt looking resistor, maybe a black burn spot on the circuit board. Things of that sort. What I meant by poking around in there is alot of times we use non conductive things to tap on components, give them a nudge to see if they're connected properly.
A chopstick would be great for that. Just keep your actual hands off of the components. I don't know what you know and don't know about tube amps so I'm really stressing not touching things that can have high voltages. It's not pleasant getting zapped with several hundred VDC, trust me.