Vibrations causing noise

[brack23_5]

I posted this on the vintage amps forum...I'll see if anyone here can chime in...

long story short....My old band from high school got asked to play a reunion show (lame) I didn't want to but I didn't wanna be the only one to say no...The other guitarist and bassist play extremely LOUD....i had to push the bandy to keep up...now if its sitting on top of the speaker cab and a bassy note/chord is hit it makes a sound like there's a bad cable...i checked all the cables with known good ones...I plugged into into a different cab and it was fine....unless i pointed it at the head...then the vibrations caused it to do the same thing...the treble and bass controls are also noisier when turned up...and when i turn it off theres a slight pop....Im sending it off to get recapped the end of this week....is it probable theres just some faulty 40 year old caps in there???

I just dont know why vibrations would cause it to do such a thing...anyone have any similar experiences/suggestions???

also...when the volume is slightly rolled down on the guitar it hums...when rolled back further it stops....
I just ordered caps and im going to check out all the voltages see if that helps....but does anyone have an idea what it may be???

thanks

[SatelliteAmps]

Sounds like it is a 40 year old amp that needs a good servicing. Not just caps, but also tubes, rebiasing, and probably a bit of contact cleaner.

[brack23_5]

all tubes are known good....I checked all the preamp tubes...switched oput the power tubes with 3 sets of ones that are known to be good....before this night....the amp was DEAD quiet....all pots and everything....no noise whatsoever....

I'm gonna see what the caps does...if not...ill go through it and check the voltages throughout the amp...if i cant solve it ill send it off to uncle alberts....

[SatelliteAmps]

How did you check the preamp tubes, and what do you mean by all the tubes are known good?

[brack23_5]

the three sets of power tubes are all tested and known to be good (two sets of Groove tubes and new old stock twin getter sylvania's)....with preamp tubes...i went through with a single ax7 which is also a tested NOS tube....and swapped it into every slot...seeing if it solved the problem....to no avail

[SatelliteAmps]

If you did all that, then it is probably the caps & service. Could be a few other possibilities, but a good tech should be able to track it down pretty fast.

[TweeDLX]

Don't forget Adam's suggestion about the contact cleaner (for tube sockets)! Clean and re-tension them.

Mike

[brack23_5]

Update: seems as though when the chasis is upside down it no longer makes the noise....I had it out of the chasis....sitting upside down (so the tubes are no longer hanging) and it was fine....no matter what i did....so i put it back in the cab...put it the right way...it began doing it again....but if i flipped the whokle cab over....it again solved the problem....One of the power tube sockets as been changed and looks kind of cheap/not soldered the best...although all the joints are inact....could this possibably be causing the problem...if the virbations were rattling this tube socket could it cause it to make such a noise?

[SatelliteAmps]

A cheap socket would not cause this. A bad solder joint could. Try re-soldering the connections on that socket (discharge the caps first).

[brack23_5]

I wanted to mention i recently noticed that with the standby on the tubes are normal...when it is off (amp is live) the power tubes glow blue....I have read in many places this is normal for some tubes (and has done this since I've owned the amp)....although what is not normal...and it used to not do this...is the blue pulsates with the speed and intensity of the tremelo...which is a weird occurance...also...seems to be more prevelant in the tube furthest away from the preamp tubes....also the one with the replaced socket....in addition....when the loud crackling happens the power tubes react with it...they get much brighter....and pulsate with the crackling....alsmost like theres a power surge or something.....any ideas???...I'm about to send it to a tech once i recap it if that doesnt somehow solve the prob.... (still waiting on the new caps to arrive)

[SatelliteAmps]

Blue glow is just gassy tubes. Not a huge deal, nor a cause of your issue.

[brack23_5]

It all turned out to be a solder joint on one of the leads for a coupling cap on the board....I did a complete cap job and re-attacthed that coupling cap....and the bandy sounds better than ever...no more pulsing tubes, no more crackling, a lot better bass response.....