5150 strange pops and noises......

[bryan_kilco]

title says it all. I've used this thing for years and never had an issue except for the FX Loop seemingly stopped working properly recently.

Played a show last Saturday. Got back, unloaded the trailer, and I was then out of town for about a week. The guys had jammed while I was away, and I noticed upon return, that some jackhole just set the amp on the concrete floor and it sat there for at least 3 days. The jam space gets cold, its a fricken shed.

Anyway, I set everything back up the other day to practice, and low and behold - the amp is making popping noises. Very similar to a bad cable or the 'pop' when you'd turn a PA system on and the speakers 'pop'. My cables, I'm 95% sure, are all good. The tubes are sorta old....but I've heard tube noise before and this is unlike any that I've heard.

Suggestions? I'll retube soon and if that doesnt solve it I guess I need to send her out.

 

[KHE]

hi

first, try a patch-cable in the fx-loop. i had a lot of amps (different brands) on my bench with bad jack-contacts in the fx-loop, because they are not often in use.
similary error-description, from scratching to popping to low-level to no-sound...

regards,
khe

 

[bryan_kilco]

hi

first, try a patch-cable in the fx-loop. i had a lot of amps (different brands) on my bench with bad jack-contacts in the fx-loop, because they are not often in use.
similary error-description, from scratching to popping to low-level to no-sound...

regards,
khe

I'll try this today. But, my problem is - I want to USE the FX loop....for my rack gear. What is the difference between plugging in just a patch cord compared to plugging in my rack?

 

[KHE]

sorry, i missunderstood you.
if you have already a cable in the fx-jacks they should be ok. (reason for patching serial-fx-loops: corrision)
bad tube-sockets can cause similary problems.
bad solder-joints to.
if you do a re-tube, clean the sockets with a good contact-spray (i recommend deoxit)
if this doesent work, i would bring the amp to a local tech.

regards, khe

 

[guitarguru777]

Yup Yup, was going to mention the FX Loop thing too. Are you currently using the Loop?

if not just plug a cable in and out of both jacks a few times to break away the corrosion on them and you should be fine.

If thats not it, re-tube it. From there if its still bad take to to a shop

 

[Omega_Void]

If thats not it, re-tube it. From there if its still bad take to to a shop

Probably good advice, but if you want to narrow down the source of trouble:

1) Does it pop when the signal into the poweramp is from external source, not from the preamp? If not your poweramp section is okay,and the problem is probably not on the supply line from the PSU either.

2) Does it pop on both preamp channels? If so your problem is in input stage (around V1a) or preamp out stage around V3B... or maybe in the switching circuitry.

If tube-swapping doesn't cure the problem... the next thing I'd check:

Popping could be caused by a leaky electrolytic capacitor which is bypassing a cathode resistor. When leak occurs, the cathode's bias drops briefly then snaps back to its normal voltage. The effect is as if a transient signal were applied to the tube's input grid.

If you're comfortable rooting around in yer head, this can be checked by removing the cathode bypass cap from the suspect triode stage. Without them the amp will be fine, but gain will be reduced, so try it like this before you put replacement caps in.

Luck, dude.

 

[bryan_kilco]

thanks guys.

Yesterday I plugged in and out of the FX loop jacks and my FX loop problem still remains.....I have to use the Preamp Out as my send because for some reason, when I have the actual Send jack used, the loop switches on, but doesnt work (tuner wont recognize strings, etc) and I get a buzz/hum.

The popping didnt happen yesterday. I'll fiddle again today a bit.

 

[Omega_Void]

The popping didnt happen yesterday.

If the popping problem is a leaky electrolytic cap, it will (probably) heal itself gradually with use. But the cap will remain weakened for a while, and will easily fail again if stressed.

...I have to use the Preamp Out as my send because for some reason, when I have the actual Send jack used, the loop switches on, but doesnt work (tuner wont recognize strings, etc) and I get a buzz/hum.

To me, that sounds most like a buggered solder joint to the Send jack.

On the 5150-II schematic, the Pre Out looks to be downstream of the Return jack. Routing the signal from the Pre Out to the Return would create a loopback in the audio chain.

 

[bryan_kilco]

If the popping problem is a leaky electrolytic cap, it will (probably) heal itself gradually with use. But the cap will remain weakened for a while, and will easily fail again if stressed.



To me, that sounds most like a buggered solder joint to the Send jack.

On the 5150-II schematic, the Pre Out looks to be downstream of the Return jack. Routing the signal from the Pre Out to the Return would create a loopback in the audio chain.

wait, so that is bad? I dont hear anything bad when doing this.

 

[guitarguru777]

Yes Bryan its bad, dont do it. Take the amp to a shop and get it looked at. Its probably due to the "rehersal" incident you talked about. i think that was you that said their 5150 got left on a cold concreete floor .... or was it the one hat had the liquid spilled in it ... cant remember

 

[bryan_kilco]

Yes Bryan its bad, dont do it. Take the amp to a shop and get it looked at. Its probably due to the "rehersal" incident you talked about. i think that was you that said their 5150 got left on a cold concreete floor .... or was it the one hat had the liquid spilled in it ... cant remember

Yes to both. Guess I'll take the Mark IV to practice tonight.

 

[InYourMemorie]

Something is wrong with my 5150 too, except mine wont even make noise anymore? I saw that you mentioned the cold, last night it was cold as fuck in my room, all my cables are new and work fine my tubes are new, i just have no idea what is going on.