Humming/vibrating transformer near power tubes

[Jcm800_6550]

My amp just started making an odd humming noise coming from the transformer near the power tubes when i turn it on ,and it seems like every once in a while it will loose all crunch and clarity and become really muddy,sometimes loses some volume , also even when the amp has no guitar plugged into it it will make a wierd low voiced "pop pop" sound coming from the speaker cabinet, is my transformer going or is it a tube problem or more, i just bought this amp off ebay so im not sure what the guy was doing with it.

Thanks for your time guys.

 

Marshall jcm 2000 dsl 100-marshall cab g1265's

[Johnny Two Tone]

Transformer hum, if present, is usually inherent in the transformer. A simple way to test for it is to just tap the unit and if the hum stays the same then you're not going to be able to get rid of the hum.

 

Aren't JMC 2000s known for having bad fans and therefore overheating issues? (I honestly don't know if this is true, it just sounds familiar to me.)

 

Since an over driven tube creates your "crunch" (assuming the crunch you speak of is tube overdrive) a loss of power level would make it so the tube never gets enough juice to get the point of break-up. Same goes for clarity. Lower wattage to the speaker's motor can equal muddy, weak sound.

 

Transformers can die over time and there really is no way to fix them cheaply... and they are expensive to replace - probably the most single expensive part of the unit.

[Jcm800_6550]

Thanks man,-Frank

[the_bleeding]

"transformer" hum can be fixed by rebiasing your powertubes.

 

Srsly. My marshall hums like nohting else. I always thought it was the power transformer, and was like eh whatever.

 

When i was biasing my homebrew, i noticed it would emit the SAME hum whenever one of the tubes drifted. All the hum went away when i matched the bias on the tubes (i have a bias circuit for each tube independently).

[Johnny Two Tone]

^Nice, I didn't think of that. My most recent run in with transformer hum was with a bunch of store lights. Each unit was a friggin' brick (rotatable pot light type things) and when 50 were added they, together, made a lot of annoying as hell hum. They were brand new; it was just the way they were (ie. Cheap Chinese made crap).

[newholland]

it could also be your power tubes hitting the end of their service cycle. as they get old, they start to drift from one another in spec, so they start to hum. if you've had 'em longer than 6-8 months of steady use-- especially if they're new stock-- think about replacing 'em and taking it in for biasing!

[Mr. Awesome]

Hello Here's the deal, go in this order -

 

1. If amp physically vobrates you have a shorted rectifier if the amp uses one. Replace the rectifier, even though it looks ok and the amp works it will seem off, weak and just weird. The shorted side is shorting to ground, and if you have wimpy transformers you will be replacing those as well if you don't get on it ASAP.

 

2. When tubes drift out of spec you get like a 60 cycle hum but the amp shouldn't vibrate.

 

3. The last thing it could be would be some component. I don't know why everyone wants to replace their transformers, I guess they like feeling they did something smart. Save your cash the transformer is most likely fine.

[Johnny Two Tone]

All you have to do is take a meter to the output of the transformer when the amp is acting weird to see if it's the transformer.