Why does my amps natural OD Sputter out?

[john]

Whenever I play with my Super Reverb cranked and let a chord sustain for a while, the natural distortion starts to sputter out and eventually be overcome with a really nasty sounding distortion. I had this problem a couple weeks ago with my amp and took it to my amp tech and literally got the amp back with new power tubes and all tuned up last week. Could this be a preamp tube issue? I am extremely frustrated beyond belief and don't want to haul my amp all the way back to the tech if I can help it.

john

[hamfist]

Yup, my first guess would be a pre-amp tube.

[phsyconoodler]

It could be you've damaged a voice coil in one or more of the speakers.If you are in the habit of 'cranking' the amp and playing flat out,the P10R's can't handle the bass or distortion for long.That's assuming you indeed have P10R's.A super puts out more bass than a P10R can handle with it's small voice coil.

[john]

Thanks, I will try replacing the #2 preamp tube and hopefully that will work. Pretty much everything else got changed when I had it serviced recently.

For speakers, I put Webers in, which I believe are capable of the higher volumes, but I usually don't dime the volume anyway, so I hope that's not the problem.

Again, thanks for your help!

john

[Blue Strat]

Originally Posted by john

Thanks, I will try replacing the #2 preamp tube and hopefully that will work. Pretty much everything else got changed when I had it serviced recently.

For speakers, I put Webers in, which I believe are capable of the higher volumes, but I usually don't dime the volume anyway, so I hope that's not the problem.

Again, thanks for your help!

john

If your webers have less than ~40 hours playing time on them, you may be hearing cone cry. This typically goes away over time but sometimes not.

Try plugging into an external speaker cabinet and see if things improve. This is the only way to know for sure.

[john]

Blue Strat,

I've had them for about 5 years now, and they've never exhibited any kind of awful distortion before, but I have a spare cab I can test it out with.

Do you agree that a bum preamp tube could also yield the kind of distortion I described?

Thanks,
john

[Blue Strat]

Originally Posted by john

Blue Strat,

I've had them for about 5 years now, and they've never exhibited any kind of awful distortion before, but I have a spare cab I can test it out with.

Do you agree that a bum preamp tube could also yield the kind of distortion I described?

Thanks,
john

Anything could cause the distortion, but speakers would be my first choice. You may have a blown speaker. The easiset thing to do is plug into another cab first.

To check the tubes, remove all but V2, V4 and V6 and play through the tremolo channel. It's safe to do this. Try the amp. If it's still fuzzy, try replacing each of the tubes with KNOWN GOOD tubes one at a time. This may help you narrow down a good tube.

You could also have a bad power tube. Check the power tube bias as well.

[john]

Thanks Blue Strat. I should have mentioned that it is not a consistent problem, which is another reason I suspect tubes. They seem to be more sensitive to, and subject to, heat and other variables than the speakers (It happens more if the amp has been on a while).

I picked up a few cheap preamp tubes on my lunch break and will try your suggestion when I get home. If it's the tubes, I'll check out what you have in stock and get some quality NOS ones. I appreciate the help!

john

[Blue Strat]

Clean all tube pins and sockets following the instructions on my website under Resources.

People usually don't believe this, but all it takes is one dirty or oxidized tube pin or socket to create 100 different symptoms in a tube amp.

[vibroverbus]

Originally Posted by Blue Strat

Clean all tube pins and sockets following the instructions on my website under Resources.

People usually don't believe this, but all it takes is one dirty or oxidized tube pin or socket to create 100 different symptoms in a tube amp.

+1.

I have a handful of unnecessarily-replaced EL84's to prove the point. They seem to love to go bad-pin-connection for some reason - crackles, pops, fizz, all intermittent and 'mysterious' but with an easy fix.

[john]

All of the sockets were cleaned and tightened less than 2 weeks ago when I had the new power tubes put in, so I should be good to go in that department, but I'll double check the pins.

Thanks again,
john