20/20 noise problems

[spikenet]

Hi, I just recently changed all my tubes to JJ's. It was ok for first few uses but now when I turn on the 20/20 it get an awefull loud hum and when I play it sounds like the guitar has tremelo effect on it.
any idea's what could be the problem? All the tube are glowing and appear to be seated correctly.

cheers.

 

[disassembled]

put all of the old ones back in and then see if the problem persists.

Greg

 

[spikenet]

hmmm, I dont have the old tubes now...

I'll take them all out, clean the pins and put them back in different places...

so I take it that its most likely a tube problem and not something more serious internally?

cheers

 

[disassembled]

probably not but if you have a bad tube then cleaning the pins isn't going to help at all. Most tube sockets are fairly clean unless you live in an area with a lot of moisture or salt in the atmosphere.

Greg

 

[spikenet]

I cleaned the pins and the sockets, swapped the tubes around and still big hum on the A channel. Could be a tube but I fear something more serious so I'm using channel B alone and will take it to a tech soon to check it out.

 

[JAZZGEAR]

Oddly enough, when I had the 2:90, I retubed it with all JJs...and had a hum I could never get rid off...until the day I traded it in to GC for a 20/20, and I took out the JJs and put in the crapiest oldest Mesa tubes I had....


....and miraculously all the hum was gone :shock:

So it could be you got a bad batch of power/preamp tubes.

 

[disassembled]

Yeah i had the same problem with 2 old JJ tubes I had laying around. I put 5 into my TA and was getting nasty popping and hissing going on until I started swapping eventually finding the two culprits. Maybe the problem is not with your 20/20 but other gear? Have you tried just plugging your guitar into each input and playing each channel separately? Did you swap the 12ax7's around too?

Greg

 

[spikenet]

Hi guys,

I did plug in the guitar straight in and still bad hum and overtones from channel A.

I might see if I can get some tubes off ebay just to test if they are faulty. Be a bit anoying if it is the tubes as I only just bought them from eurotubes.

cheers.

 

[disassembled]

Well this should be a lesson. Keep your old tubes


Greg

 

[spikenet]

took the amp to technician. Wasnt the valves after all!

Somehow wires from volume pot A got caught under the top when it was screwed on and had been crushed. Strange as I've never had thing apart, possibly it been like that since new??

Taking it out of my rack to change the tubes exacerbated the problem to the point wires were exposed and shorting ... lucky something didnt go seriously wrong!

cheers.

 

[disassembled]

There's not much voltage on those wires so there's little chance for something to go wrong. If you bought it new maybe it was loaned out to someone before you got to it?

Simple enough fix though!

Glad to see everything is working.

BTW- you should still keep your old tubes around


Greg

 

[spikenet]

seems the simple fix wasn't so simple.

Got the amp home from the tech and the hum is gone but I have horrible sound in channel A still. sounds like weird sort of harmonics when you play.

Channel B is fine tho... its very strange.

any idea's ?

cheers.

 

[spikenet]

the saga continues with the 20/20. (I have a feeling my one is a lemon!)

the tech has replaced the filter caps in the amp. apparently this has resolved nearly all the noise and harmonic issues.. however, the tech has said the fan is introducing noise in the amp.

So I was wondering if its possible to use the 20/20 without the fan? maybe drill some vent holes in the lid?

any thoughts about that..

 

[fatboy135]

feed the fan with an external power supply, anyway theorical a fan doesn´t induced noise, only if your fan starts and stops continously could induce some high frecuency voltage spikes