My 5150 head sounds like shit

[StukaJU87]

Ok, last night at practice my amp went to hell in a handbasket. I'll try to describe this as best as I can. While we were playing my amp would just suddenly increase in volume and a couple seconds later go back low again. While it is in the "low volume" stage it has a real muddy sound to it. When it kicks into the "high volume" stage it sounds almost normal.The amp hasn't been used over the winter, my band just got back into rehearsal.

My setup is like this ...guitar---pedal board----low gain input---amp set on first channel. After practice we turned the lights out so we could look at the power tubes and with the standby on the power tubes glowed orange. When the standby was turned off the furthest left power tube (looking at it from the rear) glowed blueish purple while the others stayed orange. I am guessing a retubing is in order. Any Ideas and has anyone had a similar problem?

[skidd]

Re: My 5150 head sounds like shit

It sounds like your tubes are done. If you can test with new tubes, or rearrage your old ones.

[JerryP]

Re: My 5150 head sounds like shit

Plug a jumper cord in the loop or switch the loop off with the footswitch and see what happens. The effects loop jacks can get dirty and cause all kinds of weird problems. Sometimes just plugging a cord in and out of the loop jacks a few times will clean them up.
Could be a tube problem. Volume fades is a sign of tubes but check the loop jacks first.
The 5150 have a common problem where the screen grid resistors fails. This makes the amp lose volume. If a resistor fails that power tube won't work so the amp only runs on 3 tubes (or less if more than 1 resistor is bad).
If you can't find a tech near you I do that work. I'm in Syracuse, NY. I have a bunch of 5150 info on my site.
Jerry

[Twisteramps]

Re: My 5150 head sounds like shit

What Jerry said. Plus he does killer 5150 mods...

Pete

Originally posted by JerryP:
Plug a jumper cord in the loop or switch the loop off with the footswitch and see what happens. The effects loop jacks can get dirty and cause all kinds of weird problems. Sometimes just plugging a cord in and out of the loop jacks a few times will clean them up.
Could be a tube problem. Volume fades is a sign of tubes but check the loop jacks first.
The 5150 have a common problem where the screen grid resistors fails. This makes the amp lose volume. If a resistor fails that power tube won't work so the amp only runs on 3 tubes (or less if more than 1 resistor is bad).
If you can't find a tech near you I do that work. I'm in Syracuse, NY. I have a bunch of 5150 info on my site.
Jerry

<font size="2" face="Verdana, Helvetica, sans-serif">

[CZSER]

Re: My 5150 head sounds like shit

Hey PETE (Twisteramps), I sent you a PM a week ago....Could U check it?

[Twisteramps]

Re: My 5150 head sounds like shit

Originally posted by CZ V-KNIGHT:
Hey PETE (Twisteramps), I sent you a PM a week ago....Could U check it?

<font size="2" face="Verdana, Helvetica, sans-serif">email me at [email protected] - it works a lot more reliably than PMs for me. Thanks.

pete

[StukaJU87]

Re: My 5150 head sounds like shit

Originally posted by JerryP:
Plug a jumper cord in the loop or switch the loop off with the footswitch and see what happens. The effects loop jacks can get dirty and cause all kinds of weird problems. Sometimes just plugging a cord in and out of the loop jacks a few times will clean them up.
Could be a tube problem. Volume fades is a sign of tubes but check the loop jacks first.
The 5150 have a common problem where the screen grid resistors fails. This makes the amp lose volume. If a resistor fails that power tube won't work so the amp only runs on 3 tubes (or less if more than 1 resistor is bad).
If you can't find a tech near you I do that work. I'm in Syracuse, NY. I have a bunch of 5150 info on my site.
Jerry

<font size="2" face="Verdana, Helvetica, sans-serif">Thanks for the tips...still no good. Dropping it off today at Daves Sound Repair up in E.Hanover, NJ. He is a pretty good amp tech. Can't wait to get this sorted out.

[me wise majic]

Re: My 5150 head sounds like shit

Originally posted by JerryP:
I have a bunch of 5150 info on my site.
Jerry

<font size="2" face="Verdana, Helvetica, sans-serif">What's the address??

TIA,

[lerxstcat]

Re: My 5150 head sounds like shit

www.fjamods.com

[StukaJU87]

Re: My 5150 head sounds like shit

UPDATE: Got the amp back from Dave's Sound.

These were the issues:

1) The amp was running on 3 power tubes. The 3rd tube socket from the left(looking from the rear)had a bent pin that wasn't even soldered to the board. [img]graemlins/scratchhead.gif[/img] Dave said it appeared to have left the factory that way. He replaced the socket.
2) Power tubes were shot. Replaced with 4 new Phillips 6L6wbg
3) Replaced the screen resistors
4) Replaced one preamp tube.
5) Some other stuff I can't remember, and I can't read his chicken scratch on the repair ticket.

It seems fine now, it is reborn.

[HeWhoIs]

Re: My 5150 head sounds like shit

Glad to hear it's been fixed.

[Sancho]

Re: My 5150 head sounds like shit

Yeah, 5150s can be troublesome beasts...
I had mine break down on me about twice a year. Never costly repairs, mostly just involved replacing certain components with better spec'ed ones. And I never had the same thing break down twice.
Anyhoo, I eventually got fed up with it and sold it. But damn, sometimes I do miss that sound!

[JerryP]

Re: My 5150 head sounds like shit

I work on a lot of 5150's and I see very little that goes wrong with them. They're one of the most dependable amps out there. There are exceptions to the rule and I'm sure there's a few lemons out there, but for the most part they're solid.
Jerry

[Venomboy]

Re: My 5150 head sounds like shit

My friend's 5150 combo feedbacks like crazy no matter what guitar/cable is used. The clean is fine but the dirty channel is the one that howls. Could it be a bad tube?

[dimebagdolf]

Re: My 5150 head sounds like shit

I think the 5150 is kind of a noisy amp by nature due to the fact that it has so much gain.

I play a 5150 II and I have learned to control it. The noise is not THAT bad. One thing to watch out for is not overloading the gain. The highest you'll need to set it is around 7 or 8 (at the very most)

My band plays pretty loud too. I have my gain set at 7.5 and the post set at about 4 and I'm able to keep the feedback in check.

I've also been advised that the MXR Smartgate works great with the 5150 for controlling noise.

Outside of that, if the noise is out of control, it could be a preamp tube.