So.. I'm buying this 5150...

[geet73]

... for $200. I've been using it for a while, sweet amp. Butttttt.. it's not putting out as much power as it should. About a year or two ago.. it used to just get super quiet for a little while. Then it would work again.. After a few months of this.. the tubes were replaced. It still did it. After sitting around for 6 months or so, I asked my friend if I could borrow it. It didn't do the uber drop in volume.. but it's definitely not as loud as it should be. The other day, at a show I was playing.. it randomly kicked in at full volume. I had the volume on 10(it had to be that loud...), then I had to swiftly turn it down to 4 or 5.

What do you think could be the cause of this? I'm going to take it to a tech.. but I'm not sure how much I should expect this to cost.

If you have any insight on prices or on what the problem could be, please let me know.

 

[Sonixx]

Sounds like a Cold Solder joint.

Does tapping on the Amp Case make any difference?

Does it sizzle?

With the Volume low, does it Hum?

 

[geet73]

I never tried tapping it.. it used to work a while ago, when it would drop drastically in volume. A nice hit to the top made it work fine. No humming or sizzling.

It's probably 6-8 years old or so.

 

[bongolation]

A nice hit to the top made it work fine.

Yeah, sounds like a classic cold solder joint.

If so, repair time is about two seconds. Finding the spot, pulling the PCB, putting it back in, etc., etc. will probably eat up the typical two-hour minimum bench time.

 

[Farview]

check the effects loop jacks

On some amps, the effects loop is a switching jack that can get dirty and not conduct very well. try puting a 1 foot cable from the fx out to the fx in and see if the volume comes back. If it works, thats the problem and the work-around. If not, it's probably a bad solder joint like everyone said.
jason

 

[geet73]

Alright.. I'll pull it apart soon.

Thanks alot. Hopefully this fixes it.. I'll report back.

 

[geet73]

So.. my amp started doing the uber drop in volume. When this happens.. the preamp controls hardly do anything at all.

I've got it apart right now.. I took a look at the preamp section. I didn't notice any obviously bad solder connections. Around one of the pots.. it looks like the solder got a little hot when those pots were replaced. I was not aware that pots were even replaced. Heh. Could this small part of burned stuff be the cause? I also checked if any of the big capacitors were loose. Nothing. I didn't check the small stuff.

I glanced over the poweramp and preamp tube boards too. I didn't notice anything there either.

Hmm. Should I go over this a little better, or just assemble it and take it to a tech? I do have a small amount of electronics training. I took an engineering class at my tech school. What a fun class..

Hey.. while I've got it open.. anyone know any simple mods I could do?

 

[Sonixx]

if you find a cold solder joint or loose part by inspection, it'll be just luck.

but, since you have it on the bench, go to radio shack and get some freeze spray. with the amp failing, start spraying components one at a time. spray resistors and capacitors where the lead is attached to the PCB. DO NOT SPRAY THE TUBE and KEEP THE SPRAY OFF THE GLASS. this may or may not find a cold solder joint.... the gain will restore. otherwise probably take it to an amp shop.

 

[geet73]

I took the power tubes out.. I'll make sure to cover the preamp tubes. What exactly does this freeze spray do? Essentially.. couldn't I just go over every solder connection with the iron and heat them all up?

I'll have to get that spray tommorrow. It's a bit too late for it now.

 

[Sonixx]

a cold solder joint is a hi resistance connection. the freeze spray will one: lower the resistance, much colder, and two: also cause the connection to contract and hopefully connect better. it basically restores the connection for a brief period. but, it doesn't always work. it's better than going over every connection with the iron. that may cause more harm than good.

 

[geet73]

Alright.. thanks.

 

[geet73]

Wait.. when you say brief... how long will this last for?

 

[Sonixx]

Brief... I mean temporary