Static and low volume on Peavey 5150

versital · Post by **versital** » Fri Nov 16, 2012 1:01 am

I have a 5150 that makes a lot of radio like static when you flip standby on to play. After 20 seconds or so the static fades away but occasionally comes and goes at a lower amount while playing. When you flip back to standby, the static comes back and fades away. When you turn off the power(while in standby), the static comes back again with a pop and fades off.

While playing the tone of the amp sounds great but the overall volume is extremely low. at 1/4 volume (#3) amp sounds like a 15 watt combo, at 1/2 volume (#5) the amp sounds like room volume like most 100w amps sound at #2.

I've swapped power tubes and pre-amp tubes and had no effect. Bias readings are ok. I have some suspects but since the 5150 is so cheaply made and impossible to work on live without complete dis-assembly unlike SLO clones. I wanted to get some better ideas before I take on the project.

Reeltarded · Post by **Reeltarded** » Fri Nov 16, 2012 3:13 am

Any connection could be bad.

Does it sound like the preamp stays the same but the power drops, or does it sound like the gain falls off? That can be a clue. Get in there with a stick and start chopping.

Bad cathode connections or grounds anywhere are suspect.

versital · Post by **versital** » Fri Nov 16, 2012 5:09 am

I've been poking with a chopstick all day, also used a patch cable in the FX loop as suggested by a similar posting to check for corroded contacts. What puzzles me is what would cause the static once it is powered off from standby. Also the pre-amp stays the same and the gain is solid, so the issue is in the power section, i guess I'll have to pull the output tube board out to check the other side

Reeltarded · Post by **Reeltarded** » Fri Nov 16, 2012 5:28 am

This thing has lots of sub-boards? Try cleaning the contacts on the ribbon cables?

It can be that the PI tube socket is dirty or iffy too. Drove me crazy more than a time or two.

G'luck, it will pop out at you when you get there.

Davidg · Post by **Davidg** » Sun Nov 25, 2012 7:24 am

I domt know if this helps but I bought one of those new when they came out in the 90s and mine did the same thing your describing with the woosh of static when powered up or down basically. Never had any problems with it doing that while playing but those are very noisy amps and sometimed the hiss would get a little louder from interference or something.Anyway mine did that straight from the factory and your intermintent noise while playing could be unrelated although they sound the same.Hoe it helps and Good Luck!

roberto · Post by **roberto** » Sun Nov 25, 2012 10:03 am

5150 is easy to work on. Ok, it's not like smash boards, but you have fast-on connections. The main work is to unscrew all pots, but it's a four minute work.

The main thing that comes into my mind is that the stand-by switch has some problems. Try to substitute it.

Structo · Post by **Structo** » Sun Nov 25, 2012 4:38 pm

Yes could be various things that cause this.

First would be to inspect or test the standby switch.

I am not familiar with that amp but switches don't really like high DC voltage.
They arc or chatter and cause corrosion and oxidation on the contacts.

Did you try different preamp tubes (substitute one at a time with a known good tube).
I have had bad preamp tubes cause static like that including the PI tube.

I assume this is a pcb amp and as such probably has jumper ribbon cables all over the place that can cause connection problems.
Or in a high heat area can actually unsolder components such as screen resistors.

roberto · Post by **roberto** » Sun Nov 25, 2012 7:29 pm

The part that make me think about the stand-by switch is the following:

versital wrote:When you flip back to standby, the static comes back and fades away.

Structo, the 5150 has one main pcb and two small ones:
http://i6.photobucket.com/albums/y226/D ... 50Guts.jpg

Structo · Post by **Structo** » Sun Nov 25, 2012 8:18 pm

I saw that when I was looking at the amp on the web.

I just really hate all those ribbon cables and pcb mounted tube sockets.

The amount of board flexing when rolling through tubes has weakened or broken more solder joints than I care to remember.

Are the power switches on the right there?
Mini rocker switches?

[img

768]http://i6.photobucket.com/albums/y226/D ... 50Guts.jpg[/img]

roberto · Post by **roberto** » Sun Nov 25, 2012 9:42 pm

This is the second reason why i accused the stand-by switch:
[img:586:244]http://medias.audiofanzine.com/images/n ... 465388.jpg[/img]

I've always substitued preamp tubes with the amp outside the cabinet, with one hand on the pcb to avoid too much bending.

This is a nice amp to mod, mainly because it has too much unexpressed sound: bias is colder than mesa standards (around 20mA with 480V B+ and 6L6GC), clean is horrible, lead is prone to be thin. Everything can be solved easily.

Firestorm · Post by **Firestorm** » Sun Nov 25, 2012 9:45 pm

I had mind-boggling hissing and popping on a different amp that turned out to be an intermittent connection in a tube socket (tube pin and forks not mating correctly). So I'd try to retension the tube sockets (kind of annoying if they're fork types, rather than the clam shells). You could put Tech-Spray on the ribbon cable connections, but you also have to check that those connectors are really soldered well to the back of the boards. They are pretty big heat sinks and wave soldering doesn't always quite get them.

I also worked on a 5150 once where some of the bypass caps were in backwards. Which will work for awhile.

selloutrr · Post by **selloutrr** » Sun Nov 25, 2012 11:49 pm

Check your preamp tubes

benoit · Post by **benoit** » Sun Dec 09, 2012 6:52 pm

I'm troubleshooting an amp with almost this exact problem. Did you ever figure out what was wrong?

benoit · Post by **benoit** » Tue Dec 25, 2012 4:40 pm

Figured it out. It was just dirty preamp tube sockets. Someone will find this in google results someday.

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